A foamed part for preventing collapse of an automobile armrest and a method for manufacturing the same

Abstract

The application relates to the field of high polymer materials and discloses a preparation method of a foaming piece for preventing collapse of an automobile handrail. The foaming piece is constructed by using polytetrahydrofuran ether glycol and a chain extender to form a polyurethane shape memory matrix and by doping nano microcrystalline cellulose modified by isocyanate group silane. The modified filler is dispersed in the crosslinked network to block the slipping of molecular chains, and the matrix is combined with the thermal shape memory function to make the foaming piece actively recover residual deformation under the triggering of heat, so that anti-collapse support is provided. The preparation method matches the reaction rates of foaming gas production and gel setting through a double-catalyst system, and controls the closed cell rate and the core-surface density difference of the foaming piece through a short-time high-speed mixing process, so that the filler is uniformly dispersed, and finally, the foaming finished product with uniform internal and external structures and meeting the basic tensile strength is prepared.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, and more specifically, to a foamed component for preventing collapse in automobile handrails and its preparation method. Background Technology

[0002] As an important interior component providing arm support for the driver and passengers, car armrests are typically composed of an outer leather or fabric covering and an inner soft foam component. The physical elasticity and support capacity of the internal foam component directly determine the cushioning comfort of the occupants during driving and the overall quality experience of the cabin.

[0003] In real-world driving scenarios, drivers or passengers often habitually rest their elbows on a specific area of ​​the armrest during long journeys. When subjected to this prolonged, high-intensity, concentrated pressure at a single point, the microscopic pores in conventional foam materials fatigue and lose their resilience, resulting in noticeable, irreversible indentations on the armrest surface. This permanent collapse not only severely damages the smoothness and aesthetics of the car's interior but also causes occupants to come into contact with the rigid framework beneath the foam during subsequent use, resulting in a harsh, uncomfortable feel and significantly reducing the driving and riding experience. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, the present invention provides a foam component for preventing collapse of car armrests and its preparation method, solving the technical problem of needing a car armrest foam component that can resist long-term single-point pressure from occupants, avoid permanent indentation, and continuously maintain a good support and comfort experience.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides a method for preparing a foamed component for preventing collapse in automotive armrests, comprising the following steps: S1. Place 80-120 parts by weight of polytetrahydrofuran ether diol into a reactor and heat to melt. Then add 2-4 parts by weight of modified nanocrystalline cellulose and dehydrate under vacuum to form a mixed pre-prepared base liquid. S2. Nitrogen gas is introduced into the reaction vessel, and 40-60 parts by mass of diphenylmethane diisocyanate are added dropwise to the mixed pre-prepared base liquid at a uniform rate. After the addition is completed, the mixture is stirred at a constant temperature to fully react and synthesize a prepolymer with isocyanate end groups on the molecular chain and containing uniform microcrystalline cellulose. S3. Mix 5-10 parts by weight of 1,4-butanediol, deionized water, 2-5 parts by weight of polysiloxane-polyoxyethylene ether copolymer, 0.1-0.5 parts by weight of 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine and 0.1-0.5 parts by weight of zirconium acetylacetonate evenly to prepare a mixed additive. S4. Start the high-speed stirring device and quickly add the mixing aid to the prepolymer, and mix at high speed of 2000~4000 rpm for 4~8 seconds. S5. After mixing, quickly inject the foaming mixture into the preheated mold and close the mold. After curing, open the mold and take out the molded foamed part. Perform curing annealing treatment on the molded foamed part and then let it cool naturally to room temperature to obtain a car armrest foamed part with shape memory function.

[0007] As a preferred embodiment of the method for preparing the anti-collapse foamed component for automobile armrests according to the present invention, in step S1, the amount of polytetrahydrofuran ether diol added is 100 parts, the amount of modified nanocrystalline cellulose added is 3 parts, and the modifier used for the modified nanocrystalline cellulose is isocyanate-based silane.

[0008] In a preferred embodiment of the method for preparing the anti-collapse foam component for automobile handrails according to the present invention, in step S2, the amount of diphenylmethane diisocyanate added is 50 parts.

[0009] In a preferred embodiment of the method for preparing the anti-collapse foam component for automotive armrests according to the present invention, in step S3, the amount of 1,4-butanediol added is 7.5 parts, the amount of deionized water added is 1.5 to 3.5 parts, the amount of polysiloxane-polyoxyethylene ether copolymer added is 3.5 parts, the amount of 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine added is 0.3 parts, and the amount of zirconium acetylacetonate added is 0.35 parts.

[0010] As a preferred embodiment of the method for preparing the anti-collapse foam component for automobile handrails according to the present invention, in step S4, the high-speed impact mixing parameter is 3000 rpm for 6 seconds.

[0011] As a preferred embodiment of the method for preparing the anti-collapse foamed component for automobile armrests according to the present invention, in step S1, the temperature of the reaction vessel is maintained at 70~90℃, and the dehydration process is continuously stirred at a speed of 700~900rpm for 1~3h.

[0012] As a preferred embodiment of the method for preparing the anti-collapse foamed component for automobile armrests according to the present invention, in step S2, the rotation speed is maintained at 700~900 rpm, and after dehydration is completed, the temperature of the reaction vessel is adjusted to 60~80℃. The uniform dripping time is controlled at 20~40 min. After the dripping is completed, the mixture is stirred for 1~3 h, and then naturally cooled to 35~45℃. Stirring is stopped and the mixture is sealed for later use.

[0013] In a preferred embodiment of the method for preparing the anti-collapse foamed component for automobile handrails according to the present invention, in step S5, the injection process into the mold is controlled within 2 seconds, the preheating temperature of the mold is 55~70℃, and the curing time is 8~12 minutes.

[0014] In a preferred embodiment of the method for preparing the anti-collapse foamed component for automobile handrails according to the present invention, in step S5, the molded foamed component is annealed at 70~90℃ for 3~5 hours.

[0015] A foam component for preventing collapse in automotive armrests is prepared by the above method, wherein: the microstructure of the foam component includes a shape memory cross-linked network composed of alternating flexible polyether soft segments and rigid polyurethane hard segments, and the isocyanate-based silane-modified nanocrystalline cellulose is uniformly embedded in the shape memory cross-linked network, serving as a physical anchoring node and interpenetrating with the polyurethane macromolecular chains to form a three-dimensional fatigue-resistant skeleton that impedes the slippage of molecular chains under pressure.

[0016] The beneficial effects of this invention are as follows: a polyurethane shape memory matrix is ​​constructed using polytetrahydrofuran ether diol and a specific chain extender, and nanocrystalline cellulose modified by isocyanate-based silane coupling is introduced. The modified nanocrystalline cellulose can be uniformly dispersed and anchored in the polymer cross-linked network, inhibiting the slippage of molecular chains under long-term pressure, thereby endowing the foamed part with dynamic fatigue resistance. The foaming system has a thermo-induced shape memory function. After residual deformation occurs due to long-term pressure, triggered by the temperature rise caused by the vehicle interior environment or human body temperature conduction, the internal hard segment micro-regions can be untied and drive the foamed part to actively return to its initial shape, achieving long-term anti-collapse support while maintaining the soft and cushioning feel of the foam material.

[0017] By balancing the kinetic rates of foaming gas generation and skeleton gelation reactions using a dual-catalyst system, and with optimized high-speed impact mixing parameters, the foaming liquid maintains a stable rheological state during mold filling. This effectively avoids structural defects such as macroscopic bubble collapse, closed-cell shrinkage, and severe density delamination between the core and skin caused by reaction out-of-step, ensuring the consistency of cell size and density uniformity within the foamed part. Optimized stirring and curing processes enable the modified nanofiller to be fully dispersed without damaging the nascent polyurethane network, further improving the overall tear resistance and production stability of the finished product, meeting the needs of large-scale injection molding. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 The figure shows the experimental results of optimizing the ratio of soft and hard segments.

[0020] Figure 2 The figure shows the experimental results of the synergistic optimization of the ratio of chain extender and foam stabilizer.

[0021] Figure 3 The figure shows the experimental results of optimizing the amount of modified and reinforced filler added.

[0022] Figure 4 The figure shows the experimental results of optimizing the amount of dual catalysts.

[0023] Figure 5 Figure showing the experimental results for optimizing the high-speed impact mixing process.

[0024] Figure 6 Flowchart of the method for preparing anti-collapse foam components for car handrails. Detailed Implementation

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0026] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0027] Secondly, the term "one embodiment" or "example" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The appearance of an embodiment in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that mutually excludes other embodiments. Example 1

[0028] This embodiment aims to develop a foam material system for automotive armrests that combines excellent flexibility and comfortable touch with active anti-fatigue and collapse capabilities. It addresses the problem that traditional foam components are prone to irreversible structural plastic deformation under long-term fixed-point pressure, and that simply increasing matrix density or rigidity to enhance support severely sacrifices the soft, cushioning experience required for ergonomics.

[0029] 1.1 Screening of soft segment materials This experiment aims to screen a soft segment matrix material for automotive armrest foam components that combines excellent shape memory recovery capability, excellent resistance to damp heat aging, and good ergonomic softness.

[0030] Experimental groups: A1 Polypropylene glycol (PPG, Mn=3000), A2 Polycaprolactone diol (PCL, Mn=4000), A3 Polyethylene glycol (PEG, Mn=1500), A4 Polytetrahydrofuran ether diol (PTMG, Mn=2000), A5 Hydroxyl-terminated polybutadiene (HTPB, Mn=2800), A6 Polybutylene adipate diol (PBA, Mn=2000), A7 Polycarbonate diol (PCDL, Mn=3000).

[0031] Diphenylmethane diisocyanate (40 parts) was introduced into the above candidate soft segment material (100 parts), and foamed after high-speed stirring to obtain the corresponding foamed test block.

[0032] The specimens were cut to standard dimensions and compressed to 50% of their original thickness using a universal testing machine at room temperature. This compressed state was then maintained for 24 hours using clamps to simulate the extreme collapse condition of a car armrest caused by prolonged pressure from an occupant's elbow during daily use. The physical load was then removed, and the specimens with residual deformation were placed in a preheated 45°C incubator for 1 hour to simulate the typical temperature rise environment of a car cabin under summer sunlight. After the specimens were removed and allowed to cool naturally to room temperature, their final thickness was measured, and their recovery rate was calculated.

[0033] Referring to the general damp heat aging test standard for polymer materials used in automotive interiors, the samples were placed in an environmental test chamber at 85℃ and 85% relative humidity for 168 hours continuously. The tensile strength before and after aging was tested using a universal testing machine, and the retention rate was calculated.

[0034] At a standard room temperature of 23°C, the compressive load force corresponding to the slow pressing of a sample block of specified thickness down to 25% of its initial thickness is measured. If the indentation of the car armrest is too hard, the material will feel stiff and reduce the driving experience; if it is too soft, it will not provide basic support.

[0035] A stopwatch was used to record the time interval from the end of high-speed mixing of the soft and hard sections and water, to the appearance of obvious bubbles on the surface of the mixture and the start of volume expansion (i.e., the end of the milky stage). If the initiation time window is too narrow, the mixture will undergo a gel reaction during molding, resulting in incomplete filling of the mold or even damage to the equipment; if the time window is too wide, the carbon dioxide gas generated inside will easily escape, which can easily lead to bubble collapse.

[0036] The test results are as follows: Among them, the A6 group of samples showed a high thermal shape memory recovery rate and good anti-collapse potential, but its tensile strength retention rate under high temperature and high humidity conditions was severely reduced, making it difficult to meet the stringent weather resistance requirements of the vehicle interior; the A7 group of samples showed a high retention rate of damp heat aging, but its room temperature indentation hardness value was too large, the touch was too hard, and the initiation time window was significantly beyond the reasonable range of conventional injection molding process; the A1 group of samples had a low indentation hardness, which could provide a relatively soft touch, but its shape memory recovery rate was extremely low, and it could not achieve active rebound after compression, thus failing to meet the basic requirements for fatigue collapse resistance.

[0037] In comparison, the A4 group samples demonstrated superior performance in the three core dimensions of thermally induced shape memory recovery, strength retention after damp heat aging, and room temperature indentation hardness, achieving a good balance among various performance indicators. Furthermore, its foaming time window fully met the expected requirements for industrial foaming operations. The A4 group samples effectively balanced mechanical support, environmental resistance, and ergonomic feel, ultimately leading to the selection of polytetrahydrofuran ether glycol as the baseline soft segment material for the foaming system.

[0038] 1.2 Screening of chain extenders This experiment aims to screen for a chain extender that can improve shape memory recovery rate, enhance tear resistance, and maintain a suitable balance between softness and reaction rate, based on the identified polytetrahydrofuran ether diol soft segments.

[0039] Experimental groups: B1 Ethylene glycol (EG, 6 parts), B2 Diethylene glycol (DEG, 9 parts), B3 Diethyltoluenediamine (DETDA, 11 parts), B4 1,4-Butanediol (1,4-BDO, 7 parts), B5 1,6-Hexanediol (HDO, 10 parts), B6 ​​1,2-Propanediol (1,2-PDO, 7 parts), B7 Neopentyl glycol (NPG, 9 parts).

[0040] Polytetrahydrofuran ether diol (100 parts) was mixed evenly with the corresponding candidate chain extender, and then diphenylmethane diisocyanate (40 parts) was introduced. After high-speed stirring and mixing, foaming was carried out to obtain the corresponding foamed test block.

[0041] In addition to measuring its 45℃ thermally induced shape memory recovery rate and 25% indentation hardness at room temperature, the sample needs to be cut into standard right-angled specimens (with pre-cut notches). At a standard room temperature of 23℃, both ends of the sample are fixed in the upper and lower clamps of a universal testing machine. Then, it is stretched upwards at a constant rate of 500 mm / min until the sample completely tears apart at the notch. The maximum force during the tearing process is recorded, and the tear strength (N / mm) is calculated. The hard segment micro-regions generated by the reaction of the chain extender and isocyanate constitute the anchor points of the polyurethane physical cross-linking network, directly determining the material's cohesive strength and tear resistance. If the physical cross-linking network structure constructed by the chain extender is loose, microcracks are prone to appear in the foam and rapidly propagate, leading to the breakage of the entire handrail.

[0042] Start timing with a stopwatch from the moment all components are fully mixed at high speed and poured into the container. During the gradual expansion and foaming process, use a clean, thin glass rod to repeatedly and rapidly insert it about 1 cm deep into the surface of the foam mixture at a fixed frequency of 1 to 2 seconds, then lift it vertically upwards. Stop timing when the lifted glass rod can first pull out a continuous, elastic, thin polymer thread from the mixture; the recorded time is the gel time (s) of this formulation. The polyurethane foaming process is essentially a competition between the foaming expansion reaction and the skeletal gel crosslinking reaction. The molecular structure of the chain extender and the reactivity of its functional groups directly determine the speed of the gelation reaction. Excessive chain extender activity leads to an extremely short gel time; the mixture may not be fully leveled and filled inside the mold, or the gas may not have fully expanded before the entire macromolecular network is formed, directly resulting in incomplete mold filling, closed-cell shrinkage, or even dead bubbles. Conversely, if the gel time is too long, the gas will escape before the polymer network establishes sufficient encapsulation strength, causing the sponge to completely collapse.

[0043] The test results are as follows: Among them, the B1 group samples exhibited high room temperature tear strength, but their extremely short molecular carbon chains resulted in overly dense and rigid hard segment crystalline regions within the system, causing a sharp increase in room temperature indentation hardness. The foamed parts felt extremely stiff, completely lacking the soft, cushioning feel expected of automotive armrests. The B2 group samples, due to the introduction of flexible ether bonds in their molecular structure, possessed extremely low indentation hardness and a soft feel. However, their physical cross-linking network was too loose, leading to a precipitous drop in both room temperature tear strength and thermo-induced shape memory recovery rate. This made them extremely prone to breakage and unable to effectively rebound after heating. While the aromatic amine chain extender in the B3 group showed extremely high thermo-induced shape memory recovery rate, its reactivity with isocyanates was too high, resulting in an extremely short gel time. Before the foaming mixture fully expanded and filled the mold, the macromolecular network was locked, leading to severe closed-cell shrinkage and incomplete mold filling, thus rendering the process unfeasible for industrial mass production.

[0044] In comparison, compared to the basic foaming system without a dedicated chain extender, group B4 achieved a robust improvement in thermally induced shape memory recovery, while maintaining a good and balanced level of room temperature tear strength and indentation hardness, ensuring both tensile toughness and ergonomic support. Furthermore, its moderate reactivity allowed the gel time to match the foam expansion process window, ensuring stable cell structure and complete mold filling. Ultimately, 1,4-butanediol was selected as the optimal chain extender for the system.

[0045] 1.3 Screening of fatigue-resistant modified fillers This experiment aims to screen for a high-performance nano-reinforced filler that can effectively prevent fatigue slippage of polymer chain segments under long-term pressure without damaging the original foaming pore structure and shape memory network, and is intended to enhance the fatigue collapse resistance of polytetrahydrofuran ether diol-1,4-butanediol.

[0046] Experimental groups: C1 fumed silica (4.5 parts), C2 nano titanium dioxide (4.0 parts), C3 nano calcium carbonate (8.0 parts), C4 nano microcrystalline cellulose (2.5 parts), C5 multi-walled carbon nanotubes (0.5 parts), C6 chopped glass fiber powder (6.0 parts), C7 organic intercalated modified nano montmorillonite (5.0 parts).

[0047] The above materials were added to the raw materials to prepare the corresponding foamed test blocks. In addition to measuring the 45℃ thermally induced shape memory recovery rate, room temperature tear strength, and room temperature 25% indentation hardness, it was also necessary to refer to the general dynamic fatigue testing method for flexible foam polymer materials. The standard-sized foamed blocks were placed in a dedicated fatigue testing machine. At a constant frequency of 70 times per minute, the blocks were repeatedly compressed to 75% of their original thickness, undergoing 80,000 fatigue impact cycles. This simulated the high-frequency, heavy-weight repeated pressure of an occupant's elbow on the same position of the armrest during the entire lifespan of a car under extreme conditions. After the test, the blocks were removed and allowed to recover at room temperature for 30 minutes. A high-precision thickness gauge was used to measure the irrecoverable residual thickness difference and calculate its percentage of the original thickness (i.e., the fatigue residual deformation rate). This determined whether the added micro / nano fillers truly constructed a microscopic framework network in the polymer matrix that could impede the fatigue slippage of molecular chains. The lower the residual deformation rate, the more durable the material's fatigue resistance.

[0048] Among them, chopped glass fiber powder achieved good room temperature tear strength due to its macroscopic aspect ratio advantage, but its excessive size severely damaged the microscopic pore structure inside the foamed part, resulting in poor dynamic fatigue residual deformation rate and shape memory recovery rate; fumed silica has good fatigue deformation resistance, but its extremely high oil absorption value causes the foaming system to thicken rapidly, resulting in abnormally high indentation hardness after molding and an extremely hard feel; although nano-montmorillonite maintained a good shape memory recovery rate, its layered structure is prone to interlaminar slip under long-term high-frequency pressure, resulting in a persistently high fatigue residual deformation rate; nano-calcium carbonate has the least impact on hardness, but as an inert filler, it severely interferes with the physical cross-linking network of the polymer, resulting in a significant decrease in recovery rate.

[0049] Nanocrystalline cellulose exhibits excellent performance in terms of dynamic fatigue residual deformation rate under constant load, thermally induced shape memory recovery rate at 45℃, and room temperature indentation hardness. However, its room temperature tear strength decreases significantly. This is because the unmodified nanocrystalline cellulose surface contains a large number of strongly polar hydroxyl groups, which cause severe physical aggregation in the weakly polar polyurethane system. These aggregates not only fail to provide dispersion reinforcement but also become macroscopic defects and stress concentration points under stress, making the material extremely prone to tearing. Subsequent experiments only need to address the tear strength degradation caused by these aggregates by introducing surface coupling modification treatment.

[0050] 1.4 Screening of Surfactants Experimental groups: D1 Sodium dodecylbenzenesulfonate, D2 Stearic acid, D3 Titanate coupling agent, D4 Isocyanate-based silane coupling agent, D5 Aluminate coupling agent, D6 Aminosilane coupling agent, D7 Terminal epoxy silane coupling agent.

[0051] A surfactant was dissolved in an appropriate amount of anhydrous ethanol to prepare a modified solution. Nanocrystalline cellulose was then slowly added to the solution, and the mixture was ultrasonically dispersed and mechanically stirred at 60°C for 2 hours. After the reaction, the mixture was centrifuged and washed repeatedly with ethanol to remove unreacted modifier. Finally, it was dried in an 80°C vacuum oven to constant weight, yielding seven groups of nanocrystalline cellulose with different surface modifications. Corresponding foaming test samples were then prepared.

[0052] In addition to measuring its room temperature tear strength, constant load dynamic fatigue residual deformation rate, and 45℃ thermally induced shape memory recovery rate, during the preparation of the foamed sample block, after the filler and polytetrahydrofuran ether glycol are mixed at high speed and vacuum dehydrated, a 100ml sample of the mixture is separately injected into a standard graduated stoppered cylinder. The cylinder is placed in a constant temperature environment at 25℃ and left to stand for 24 hours. After standing, the volume of the obvious white solid precipitate layer appearing at the bottom of the cylinder is observed and recorded, and the percentage of the precipitate layer volume to the total volume of the mixture (i.e., sedimentation rate) is calculated. This is used to evaluate whether the surfactant has successfully changed the surface polarity of the nanocrystalline cellulose, enabling it to achieve long-term suspension stability and nanoscale dispersion in the polymer matrix.

[0053] Among them, aminosilane coupling agents achieved good room temperature tear strength, but the localized over-crosslinking they induced made the material brittle and prone to micro-fracture under long-term dynamic pressure, resulting in the lowest fatigue residual deformation rate. Stearic acid treatment resulted in extremely low sedimentation rate (excellent dispersibility), but its long carbon chains acted like plasticizers, remaining free in the system and severely weakening the original physical crosslinking force of the polymer network, leading to a low shape memory recovery rate. Although group D3 performed well in dynamic fatigue residual deformation rate, its interfacial bonding with the polyurethane matrix was weak, resulting in poor room temperature tear strength. Group D7 retained a high shape memory recovery rate, but due to the severe mismatch between its end group polarity and the polyether matrix, the filler quickly flocculated and settled, resulting in the worst static sedimentation rate and easily causing blockage in production pipelines. Isocyanate-based silane coupling agents have excellent overall performance, so they were selected as surface modifiers for nanocrystalline cellulose.

[0054] 1.5 Screening of foaming agents This experiment aims to screen a surface-active foaming agent that can ensure the macroscopic density uniformity of the foamed parts, accurately control the balance of open and closed pores, and not damage the existing shape memory network and comfortable feel, based on the aforementioned determined matrix and modified filler system.

[0055] Experimental groups: E1 Tween 80 (1.2 parts), E2 Hydroxyl-terminated silicone oil (1.5 parts), E3 Dimethyl silicone oil (1.0 part), E4 Polysiloxane-polyoxyethylene ether copolymer (1.5 parts), E5 Fatty alcohol polyoxyethylene ether (1.8 parts), E6 Fluorocarbon surfactant (1.0 part), E7 Octyl-modified polysiloxane (1.5 parts).

[0056] Then, foamed test samples were prepared. After the foamed samples matured, standard blocks of equal volume were precisely cut from the dense skin area that was in close contact with the inner wall of the mold and from the core area at the very center. The samples were weighed and their density values ​​(kg / m³) were calculated. 3 The density difference between the surface layer and the core was ultimately determined. During the intense chemical foaming process, the expansion of carbon dioxide gas and the gelation of the polymer skeleton occur simultaneously. If the foam stabilizer has a weak ability to reduce surface tension, small bubbles will rapidly converge towards the center and rupture and fuse, causing gas to be drawn from the surface to the core, ultimately forming a structure with a dense surface and hollow interior. The smaller the density difference between the surface and the core, the stronger the foam stabilizer's effect on the macroscopic stability and uniform distribution of bubbles, thus ensuring the consistency of the load-bearing support force in all parts of the handrail.

[0057] The volume percentage of closed pores not connected to other holes or the outside world within the foamed block was measured using the gas specific gravity bottle method. As a car armrest that needs to provide a soft cushioning feel and withstand prolonged pressure, its internal structure must primarily consist of interconnected open pores to allow for rapid gas release and stress relief under pressure. If the foam stabilizer has excessively strong foam-stabilizing activity, it will tightly seal the generated gas within individual pores, resulting in an extremely high closed-cell rate. This not only causes macroscopic shrinkage deformation of the foamed part after cooling due to the drop in internal gas pressure, but also makes the material exhibit a stiff, balloon-like rebound feel under pressure.

[0058] Continue measuring the 25% indentation hardness at room temperature and the thermally induced shape memory recovery rate at 45℃ for each group. At the microscopic level, the foam stabilizer directly determines the thickness of the foam wall and the open / closed pore state. If excessive foam stabilization leads to large-area closed pores, the trapped gas pressure will directly result in abnormally high indentation hardness, compromising the ergonomic feel. Simultaneously, some surface-active molecules with strong permeability or mismatched polarity are highly susceptible to becoming free and penetrating into the microphase separation region of the soft and hard segments of polyurethane during high-temperature curing, interfering with hydrogen bond formation like plasticizers, thus severely weakening the ability of the macromolecular network to actively recover its original shape after heating.

[0059] Among them, octyl-modified polysiloxane, although achieving an extremely low foaming closed-cell rate and making the cells highly open and breathable, its excessive hydrophobicity leads to severe uneven dispersion of water (foaming agent) in the foaming system, resulting in an extremely unstable foaming process and the formation of a large number of huge cavities inside; hydroxyl-terminated silicone oil is extremely integrated with the system, achieving the smallest surface-core density difference (most uniform internal and external density), but its foam stabilizing activity is too high, forming a large number of impermeable closed-cell structures, resulting in an abnormally high foaming closed-cell rate. This not only causes the sample to shrink after cooling, but also causes the enclosed gas to rebound sharply under pressure, causing the hardness to soar; although fluorocarbon surfactants do not interfere with the polymer's own shape memory network and achieve the highest recovery rate, their low surface tension results in extremely poor foam stabilizing ability, with a large number of pores breaking down, causing a decrease in hardness due to room temperature indentation, and the foamed part losing its basic support; although dimethyl silicone oil can provide high hardness, it forms a thick phase separation oil film in the system, which severely damages the hydrogen bonding between hard segment molecules, resulting in a low thermally induced shape memory recovery rate.

[0060] The moderate polyether / siloxane segment ratio of the polysiloxane-polyoxyethylene ether copolymer achieves a low surface-to-core density difference (extremely uniform bubble distribution), effectively controlling the foaming closed-cell rate within a reasonable low range, ensuring free airflow and retraction of internal gas under pressure. Its good compatibility avoids plasticizing interference with the polyurethane physical crosslinking network, robustly maintaining excellent heat recovery and a moderately flexible, supportive feel under pressure. Taking all factors into consideration, the polysiloxane-polyoxyethylene ether copolymer was ultimately selected as the surface tension modifier for the foaming system.

[0061] 1.6 Screening and Optimization of Dual Catalyst Ratio In actual industrial injection molding, water-driven foaming and gas generation and polyol-driven skeletal crosslinking are a pair of highly competitive dual-track reactions. Relying solely on the natural reaction rate of the system can easily lead to macroscopic bubble collapse or closed-cell shrinkage due to uncontrolled synchronization. It is necessary to ensure that the foaming liquid achieves precise locking of the physical network when filling the mold, so as to maximize the stability of the material's fatigue-resistant shape memory substrate while ensuring the yield of industrial molding.

[0062] The foaming gas-generating catalysts are: F1 bis(dimethylaminoethyl) ether (BDMAEE), F2 pentamethyldiethylenetriamine (PMDETA), F3 N,N-dimethylcyclohexylamine (DMCHA), F4 N,N,N',N'-tetramethylhexanediamine (TMHMDA), F5 dimethylethanolamine (DMEA), F6 N,N,N'-trimethyl-N'-hydroxyethyldiaminoethyl ether, F7 tetramethylbutanediamine (TMBDA), F8 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine, F9 N-methyldicyclohexylamine, and F10 N,N-dimethylbenzylamine (BDMA).

[0063] Skeletal crosslinking catalysts: G1 Triethylenediamine (TEDA), G2 Dibutyltin dilaurate (DBTDL), G3 Stannous octoate, G4 Bismuth isooctanoate, G5 Zinc isooctanoate, G6 Dimethyltin dinedecanoate, G7 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), G8 1,4-dimethylpiperazine (DMP), G9 1,2-dimethylimidazole, G10 Zirconium acetylacetonate.

[0064] 1.6.1 Test Experiment on the Reaction Rate of Foaming and Gas Generation A measured amount of water and sufficient diphenylmethane diisocyanate were mixed in a reaction vessel. 0.5 parts of each candidate foaming and gas-generating catalyst (F1-F10) were added separately, with a blank group without any catalyst used as a control. After mixing at high speed for 5 seconds, the isocyanate groups (-NCO, characteristic peak at 2270 cm⁻¹) were monitored in real time using an infrared spectroscopy instrument. -1 The rate at which the -NCO group is converted into a urea bond by the reaction with water is recorded. The time required from the end of mixing to when the conversion rate of the -NCO group reaches 50% is defined as the half-life initiation time (s). The shorter the time, the faster the catalyst drives the production of carbon dioxide gas.

[0065] 1.6.2 Test of skeleton crosslinking reaction rate In a completely anhydrous environment (excluding interference from gas-generating reactions), pre-vacuum-dehydrated polytetrahydrofuran ether glycol, 1,4-butanediol, and diphenylmethane diisocyanate were mixed. 0.2 parts of each candidate backbone crosslinking catalyst (G1-G10) were added, with a blank group without catalyst serving as a control. Mechanical stirring was maintained at a constant temperature (40°C), and the viscosity change of the reaction mixture was monitored in real time using a rotational viscometer. The time required for the system viscosity to jump abruptly from the initial state to 10000 mPa·s (indicating the beginning of crosslinking and freezing of the macromolecular network) was recorded and defined as the critical gel time (s). The shorter this time, the faster the catalyst locks in the polyurethane backbone.

[0066] The test results are as follows: Foaming gas-generating catalysts require a half-life ignition time greater than 8 seconds (to allow time for filling the mold and prevent ignition within the die head or runner) and less than 20 seconds (to ensure the gas can rapidly expand and fill the mold). F3, F4, F6, F7, and F8 meet this requirement. Framework crosslinking catalysts require a critical gel time that lags behind the ignition and expansion period, but not too late; the optimal window is set between 10 and 30 seconds (when the gas fills the mold, the framework just begins to solidify). G3, G4, G6, G7, and G10 meet this requirement.

[0067] 1.6.3 Environmental Sensitivity Assessment Test For the five foaming gas-generating catalysts and five framework crosslinking catalysts that passed the initial screening, an evaluation based on their sensitivity to extreme environments is necessary to avoid frequent adjustments to catalyst formulations and preparation process parameters due to seasonal temperature and humidity changes in the workshop during actual industrial production. Polyurethane reactions are inherently exothermic and extremely sensitive to moisture. Catalysts that perform well in traditional constant temperature and humidity laboratories are highly susceptible to drastic changes in reaction rates under abnormal temperature and humidity conditions. For example, high temperature and high humidity can easily lead to thermal runaway and introduce large amounts of unplanned moisture, disrupting the reaction ratio, while low temperature and low humidity may cause catalyst deactivation. Therefore, screening for catalysts that can withstand complex external temperature and humidity fluctuations and maintain highly robust reaction kinetics is crucial for achieving year-round, adjustment-free production of the formulation.

[0068] This test utilizes a walk-in high and low temperature alternating humidity test chamber, selecting three ambient temperature gradients (10℃, 25℃, 35℃) and three ambient relative humidity gradients (30%, 55%, 85%). By orthogonally combining temperature and humidity in pairs, nine sets of mutually overlapping test conditions are constructed to comprehensively cover various real workshop environments.

[0069] In the aforementioned cross-test conditions, the raw material ratios and mechanical stirring parameters from the independent tests were kept constant, and the half-life, initiation time, and critical gel time of each candidate catalyst were re-determined. The reaction time of each catalyst group under different conditions was recorded, and the standard deviation of its reaction time was calculated. The smaller the standard deviation, the stronger the catalyst's resistance to environmental temperature and humidity disturbances, and the higher its robustness and industrial tolerance in cross-environmental operations.

[0070] The test results are as follows (the table has been split for easier display): Continued: Comparative analysis of the cross-test data on environmental sensitivity revealed that each candidate catalyst possesses its own relatively adaptable low-fluctuation comfort zone. While 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine and zirconium acetylacetonate, although not entirely free from fluctuations during individual adjacent environmental transitions, exhibited extremely strong resistance to environmental interference within the complete test matrix. The combined reaction time standard deviation of both catalysts was the lowest among all tested components, locking the reaction initiation and gelation time windows within a safe and highly controllable range. Considering both process robustness and the need for no adjustments, 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine was ultimately selected as the foaming catalyst, and zirconium acetylacetonate as the framework crosslinking catalyst. Example 2

[0071] Reference Figures 1-4 This is the second embodiment of the present invention. Following the systematic screening of the core components of the anti-collapse automotive armrest foam system in Example 1, this embodiment aims to optimize the formulation components determined in Example 1 based on the established benchmark formulation, in order to explore the optimal equilibrium point of the reaction system.

[0072] 2.1 Optimization of the ratio of soft and hard segments This experiment aims to explore the optimal mass ratio between polytetrahydrofuran ether diol (soft segment material) and diphenylmethane diisocyanate (hard segment material). The ratio of soft to hard segments directly determines the degree of microphase separation within the polyurethane foam material, thus dominating the core performance characteristics of the automotive armrest, including its mechanical support strength, tactile softness, and shape memory recovery.

[0073] While maintaining a uniform addition of 100 parts of polytetrahydrofuran ether diol, the addition of diphenylmethane diisocyanate was set to vary from 30 to 70 parts in increments of 5 parts. Corresponding foaming test samples were prepared. The formulation performance was comprehensively evaluated by testing the thermally induced shape memory recovery rate at 45℃, the 25% indentation hardness at room temperature, the tear strength at room temperature, and the dynamic fatigue residual deformation rate under constant load.

[0074] Test results are as follows Figure 1 As shown, through data fitting, the theoretical maximum point of thermally induced shape memory recovery rate was calculated to be 58.4 parts, the theoretical peak value of room temperature tear strength was 48.6 parts, and when the addition amount was , the minimum value of dynamic fatigue residual deformation rate was 43.2 parts. When the addition amount was 47.5 parts, its indentation hardness fell exactly at the optimal comfortable touch target value of 145N.

[0075] The arithmetic mean of the hard segment addition amounts corresponding to the aforementioned key theoretical extreme points was calculated, yielding a global theoretical optimal ratio of 49.42 parts that takes into account overall comprehensive performance. Considering the accuracy setting and operational convenience of the metering system in large-scale industrial injection molding production, 50 parts were ultimately selected as the final optimized baseline ratio for diphenylmethane diisocyanate (hard segment material).

[0076] 2.2 Synergistic optimization of the ratio of chain extender and foam stabilizer In foaming systems, chain extenders determine the tightness and microscopic strength of the physical cross-linking network, while foam levelers control the surface tension of bubbles and the uniformity of the macroscopic pore structure. A strong interplay exists between the two during the foaming and setting process: an excessively high proportion of chain extender leads to rapid rigidification of the bubble walls; if the proportion of foam leveler is inappropriate at this point, it can easily cause large-scale shrinkage of closed cells or bubble rupture. Conversely, if foam levelers are overused in pursuit of finer pores, the network strength established by the chain extender will be weakened. Therefore, this experiment aims to explore the optimal synergistic ratio of chain extenders and foam levelers during the dynamic foaming process.

[0077] The addition gradient of the chain extender was set from 1 part to 10 parts (1 part increment, 10 gradients in total), and the addition gradient of the foam stabilizer was set from 0.5 parts to 5.0 parts (0.5 parts increment, 10 gradients in total). The two sets of variables were combined in a completely orthogonal manner to prepare control test blocks.

[0078] Referring to the general testing standards for environmental reliability of automotive interior parts, the samples were placed in a programmable high and low temperature alternating test chamber. The cycle program was set as follows: holding at -40℃ for 2 hours, followed by a rapid increase to +85℃ within 30 minutes and holding for 2 hours, which constitutes one complete cycle. After 20 consecutive cycles of hot and cold alternating, the samples were removed and left to stand at room temperature for 24 hours, and the maximum percentage shrinkage of each dimension compared to the initial state was measured. Under extreme thermal expansion and contraction shocks, if the foaming agent distributes uneven cell stress, or if the cross-linking toughness and cell wall thickness of the chain extender-constructed skeleton are severely imbalanced, large-scale micro-tears and macro-collapse shrinkage will occur inside the foamed part. This indicator can most intuitively reflect the degree of synergy and self-consistency between the two in controlling internal air pressure and resisting external stress.

[0079] A standard-sized foamed sample was placed between two parallel plates of a universal testing machine. At a standard room temperature of 23°C, the sample was unidirectionally compressed vertically at a constant rate of 10 mm / min until the deformation reached 50% of its initial thickness. The maximum compressive load during this compression process was recorded and converted into compressive strength (kPa). Although increasing the absolute amount of chain extender usually improves the theoretical strength of the matrix, in actual foaming processes, if an imbalance in the proportion of foaming agent leads to severe macroscopic defects such as co-occurrence, voids, or uneven closed-cell structures, the compressive strength will catastrophically decrease due to the lack of stress-bearing area and stress concentration. This index aims to determine whether the true contribution of the chain extender to the strength of the matrix is ​​offset by the deterioration of the cell structure.

[0080] Test results are as follows Figure 2 As shown, the shrinkage rate and compressive strength under high and low temperature alternating cycles exhibit a highly regular ridge-shaped distribution in three-dimensional space as the amount of chain extender and foam stabilizer added varies. This means that the optimal regions for both indicators are not isolated extreme points, but rather form a continuous valley line of low shrinkage rate and a ridge line of high compressive strength along a specific chain extender / foam stabilizer ratio line. Once deviating from this ratio line, whether increasing or decreasing a single component, the performance will deteriorate drastically to the quadratic degree due to the imbalance of air pressure in the micro-crosslinks and macro-cells.

[0081] Through multivariate quadratic polynomial regression and partial differential equation calculations, the theoretical absolute extreme point coordinates of the high and low temperature alternating cycle shrinkage rate are obtained as (7.15, 3.08), while the theoretical absolute extreme point coordinates of the compressive strength are (8.03, 3.96). Further linear regression analysis of the ridge projections constituting their respective extreme value regions yields the following approximate regression equations for the optimal synergistic ratio of shrinkage rate: y(foaming agent) = 0.402x(chain extender) + 0.185; and for compressive strength, y = 0.455 + 0.124.

[0082] In practical applications, it is necessary to simultaneously consider extreme temperature deformation stability and the basic skeletal support. The coordinates of the two-dimensional intersection point are (7.55, 3.42). This intersection point is very close to the absolute extreme points of both individual indicators, located within their shared smooth and efficient region, representing the global Pareto optimal solution under the dual game of macroscopic physical network and microscopic cell structure. Considering the control precision of metering pumps and the convenience of process setting in industrial production, and given the extremely gentle surface gradient near this intersection point, where small deviations will not cause abrupt performance changes, a chain extender of 7.5 parts and a foam leveler of 3.5 parts are selected as the optimal synergistic shaping ratio for this foaming system.

[0083] 2.3 Optimization of Modified Reinforcing Filler Dosage This experiment aimed to explore the optimal doping amount of isocyanate-modified silane-based nanocrystalline cellulose in a foaming system. The nanoscale rigid one-dimensional crystals, acting as a microscopic framework interspersed within the polyurethane network, significantly impede fatigue slippage of polymer chains under long-term stress. The doping of any nanoparticle has a critical threshold for physical dispersion; insufficient addition makes it difficult to form a continuous anti-fatigue network, while excessive addition inevitably leads to secondary agglomeration and a sharp increase in the initial viscosity of the system, thereby deteriorating the material's resistance to damage and severely hindering the foaming expansion process.

[0084] While maintaining the previously determined baseline component ratio, the addition gradient of modified nanocrystalline cellulose was set as follows: 0.5 parts, 1.0 parts, 1.5 parts, 2.0 parts, 2.5 parts, 3.0 parts, 3.5 parts, 4.0 parts, 4.5 parts, and 5.0 parts. Corresponding foaming test samples were prepared.

[0085] Referring to the standard of 80,000 high-frequency dynamic fatigue compression tests, the percentage of irreversible residual thickness of the sample after undergoing ultimate fatigue impact was measured. This is the absolute core criterion for evaluating whether the modified nanocrystalline cellulose has successfully constructed an anti-fatigue microstructure; the lower the value, the stronger the system's ability to resist long-term compression and collapse. Then, the room temperature tear strength was tested.

[0086] In an open, wide-mouthed container, the quantitatively mixed foaming liquid is completely released, and its final volume after the foaming reaction has completely ended and it has matured and set is recorded as the ratio (expressed as a multiple or percentage) to the initial liquid volume before mixing. The introduction of a large amount of nano-solid powder will exponentially increase the initial kinetic viscosity of the polyol component. If the viscosity is too high, the carbon dioxide gas produced by the chemical reaction will have difficulty overcoming the viscous resistance of the liquid to expand freely.

[0087] Test results are as follows Figure 3 As shown, the extreme point of room temperature tear strength is 2.38 parts; when the addition amount is 3.25 parts, the fatigue slip of the polymer chain segments is locked to the maximum extent, and the dynamic fatigue residual deformation rate under constant load is reduced to the minimum; while when the addition amount is 3.16 parts, the free expansion rate of the mixture just falls back to 18.0 times the industrial safety lower limit, and if it continues to be added, there will be a serious risk of material shortage or dead foam. The arithmetic mean of the above three key theoretical points is calculated to obtain the global theoretical optimal ratio point of 2.93 parts, which can take into account both the construction of micro-anti-fatigue network and the rheological constraints of macro-foaming process. Considering the convenience of weighing and feeding in industrial production and the fault tolerance of systematic error, and at the same time, this theoretical point is very close to the nearest 0.5 step gradient, 3.0 parts is finally selected as the final optimized benchmark ratio of isocyanate-based silane modified nanocrystalline cellulose in the foaming system.

[0088] 2.4 Optimization of Dual Catalyst Dosage In actual mold forming, the absolute amount and relative ratio of these two catalysts directly affect the two reaction trajectories: foaming expansion (gas production and volume expansion) and gel setting (skeleton locking). The degree of synchronous engagement between the two determines whether the finished product is internally dense and full, or macroscopically collapsed or closed-cell shrinkage.

[0089] The addition amounts of both the foaming gas-generating catalyst and the framework crosslinking catalyst were set to a gradient from 0.1 parts to 1.0 parts, with a step size of 0.1 parts. These two sets of variables were orthogonally combined to prepare foaming mixtures containing different ratios of the two catalysts. These mixtures were then injected into molds for foaming to obtain control test samples.

[0090] In addition to measuring the density difference of the core and the thermally induced shape memory recovery rate at 45℃, a fully automated true density meter (gas specific gravity bottle method) is also needed to directly determine the volume ratio of unconnected closed air bubbles inside the foamed sample. If the gel solidifies too quickly, the polymer skeleton will be rigidly frozen before the gas breaks through the bubble walls, resulting in an abnormally high closed-cell rate and causing severe shrinkage of the foamed part after cooling. If the foaming and gas generation are too fast and the skeleton is weak, the gas will break through the pore walls on a large scale and escape, resulting in an extremely low closed-cell rate and structural bubble collapse.

[0091] Test results are as follows Figure 4As shown, response surface fitting and comprehensive analysis of the test data revealed that the dual catalysts have a sensitive synergistic window when controlling the foaming reaction process. When the proportion data is distributed along a trajectory of approximately y=0.83x+0.11, the closed-cell rate can be stabilized at 15%~28%, which is a comfortable semi-open-cell range suitable for the free breathing of soft armrests.

[0092] Partial differential calculations were performed on the fitted surface. When the foaming agent was 0.25 parts and the gelling agent was 0.25 parts, the density gradient difference reached a minimum (the internal and external structures were most uniform); while when the foaming agent was 0.42 parts and the gelling agent was 0.45 parts, the shape memory recovery rate reached a theoretical maximum.

[0093] In actual industrial molding processes, extremely small density differences are needed to ensure a consistent feel and prevent delamination across all parts of the handrail, while also requiring a very high recovery rate to resist long-term fatigue and collapse. Simply choosing either extreme point would weaken the other core performance characteristic. Since the coordinates of both theoretical extreme points fall within the safe target range for closed-cell ratio, the arithmetic mean yields 0.335 parts of foaming agent and 0.35 parts of gelling agent.

[0094] Considering the metering accuracy and ease of feeding of the catalyst micro-pump in actual production, and the extremely gentle surface gradient near the theoretical intersection point, this experiment, after reasonable rounding, finally determined that 0.3 parts of 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine and 0.35 parts of zirconium acetylacetonate should be used as the final catalyst ratio for this composite foaming system. Example 3

[0095] Reference Figure 5 This is the third embodiment of the present invention. After screening all the core components of the anti-collapse car armrest foaming system and systematically calculating the optimal synergistic ratio of each component under a laboratory-level ideal model, the volume-to-surface area ratio of the system undergoes a dramatic change during the scaling-up from gram-level laboratory trials to hundred-kilogram-level industrial mass production. This leap in scale causes minor variables that were originally masked or even did not affect the reaction in small-scale test containers due to rapid heat dissipation or instantaneous shear (such as local heat accumulation, microbubble entrainment, macroscopic sedimentation of microcrystalline cellulose, and uneven temperature field in large-scale molds) to be simultaneously and exponentially amplified to a fatal degree sufficient to completely destroy the foaming network, change the reaction trajectory, or cause structural collapse. Therefore, this embodiment aims to optimize the industrial-scale process parameters for multiple stages of preparation based on the finalized formulation.

[0096] 3.1 Melting and Dehydration Composite Process of Soft Segment Resin and Nanofiller 100 parts by weight of solid polytetrahydrofuran ether diol were added to a large-capacity jacketed and heated reactor. The heating system was turned on, and the temperature inside the reactor was gradually increased and maintained at 700-900 rpm, causing the polyether soft segment material to melt into a homogeneous liquid. After the soft segment resin was completely liquefied, 3 parts by weight of nanocrystalline cellulose, which had been surface-modified with isocyanate-based silane coupling agent, were slowly and evenly added to the reactor in batches through a sealed feeding port. Simultaneously with the feeding, a high-speed mechanical agitator inside the reactor was started, with the speed set to 700-900 rpm for strong shear dispersion.

[0097] After feeding is completed, seal the reactor and, while maintaining a constant temperature and strong mechanical stirring at 700~900rpm, start the vacuum pump to continuously dehydrate the inside of the reactor under vacuum, with the dehydration time controlled at 1~3h.

[0098] 3.2 Synthesis process of isocyanate-terminated prepolymers After completing vacuum dehydration and strong dispersion, the vacuum state of the reactor is released, and dry high-purity nitrogen gas is continuously introduced into the reactor to form an inert protective pressure and prevent moisture from the air from being drawn back in. The temperature of the mixed base liquid in the reactor is steadily reduced from 80℃ to 60~80℃ using jacket cooling water and precisely maintained at a constant temperature.

[0099] Under nitrogen protection and constant conditions, 50 parts by weight of diphenylmethane diisocyanate were added dropwise into the reactor at a uniform rate using a precision metering pump. To prevent the isocyanate from generating violent exothermic reactions upon contact with the polyol, which could lead to localized explosive polymerization or excessive cross-linking of macromolecules, the entire dropwise addition process was strictly controlled within 20–40 minutes.

[0100] After the addition is complete, maintain the temperature inside the reactor at 60-80℃ and continue mechanically stirring for 1-3 hours. Ensure that the hydroxyl groups at the ends of the soft-segment resin undergo a sufficient pre-addition reaction with the sufficient amount of diphenylmethane diisocyanate, ultimately synthesizing a stable prepolymer with active isocyanate end groups on the molecular chain and uniformly suspended and encapsulated nanocrystalline cellulose-modified filler. After the reaction is complete, allow the prepolymer temperature to naturally decrease to 35-45℃ and store for later use.

[0101] 3.3 Formulation of foaming mixing aids and optimization of high-speed impact mixing process In another dedicated mixing container, 7.5 parts by weight of 1,4-butanediol, 2.5 parts by weight of deionized water, 3.5 parts by weight of polysiloxane-polyoxyethylene ether copolymer, 0.3 parts by weight of 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine (foaming gas-generating catalyst), and 0.35 parts by weight of zirconium acetylacetonate (skeletal crosslinking catalyst) were thoroughly mixed and stirred to form a highly homogeneous multi-component liquid mixed additive system (i.e., component B).

[0102] Subsequently, the mixing agent needs to be rapidly added to the isocyanate-terminated prepolymer (i.e., component A) that has been cooled to 40°C for high-speed impact mixing. Since the foaming and gelation reactions occur instantly upon contact between the two components, the stirring process parameters at this stage have a critical impact on the molding quality. If the stirring speed is too low or the stirring time is too short, small molecules such as water and catalysts are unlikely to achieve micron-level dispersion in the viscous prepolymer, resulting in uneven foaming, local bulging, or dead cells. Conversely, if the speed is too high or the stirring time is too long, the high-speed blades will not only brutally break the newly formed initial bubble nuclei in the system (leading to bubble collapse and abnormally high density), but will also abruptly cut off the initial polymer skeleton that is undergoing cross-linking and solidification, causing a cascade of strength loss in the finished product, or even causing the mixture to solidify instantly in the stirring chamber, resulting in a serious production accident such as jamming and machine explosion.

[0103] The stirring speed gradient was set from 1000 r / min to 5000 r / min, with a step size of 500 r / min. The stirring duration gradient was set from 3 seconds to 12 seconds, with a step size of 1 second. Cross-combination tests were conducted on these two sets of variables, resulting in 90 different mixing conditions. Immediately after mixing, the liquid must be rapidly injected into a preheated automotive armrest mold (55-70°C) within 2 seconds for curing and foaming to obtain the corresponding foamed test sample.

[0104] In addition to measuring the apparent density of the core (to monitor whether excessive shearing leads to large-scale rupture of bubble nuclei and abnormally high density caused by carbon dioxide gas loss) and the room-temperature tear strength (to determine whether the high-speed blades have brutally severed the physical cross-linking network in the early stage of gelation, leading to a collapse in toughness), it is also necessary to test the coefficient of variation of cell size (CV value) to conduct a microscopic quantitative evaluation of the mixing uniformity effect. Thin slices of the sample are cut along the center of the cross-section of the sample block, and the microscopic morphology images of the core cells are captured using a scanning electron microscope at a fixed magnification. Using image processing software, the equivalent diameters of at least 100 closed or semi-closed cells in the field of view are randomly counted, and their average diameter and standard deviation are calculated. Finally, the percentage of the standard deviation to the average value (i.e., the CV value) is obtained. During the impact mixing stage, small molecules such as water and catalysts must be torn into micron-sized droplets by strong mechanical shear forces to ensure that multiple micro-reaction points are launched simultaneously and synchronously. If the rotation speed is insufficient or the time is too short, the multiphase fluid will not be thoroughly mixed. Macroscopically, this will cause the foaming liquid to produce gas too quickly in some areas while other areas stagnate. Microscopically, this will manifest as extremely large differences in bubble size, or even the appearance of large voids and bubble co-occurrence, and the CV value will soar sharply.

[0105] Test results are as follows Figure 5As shown, by observing the surface morphology of the coefficient of variation (CV value) of cell size, it can be seen that the complete dispersion of water and additives is highly dependent on the cumulative shear work (rotation speed × time). Its optimal uniformity region is not fixed on a single coordinate, but is distributed along a valley of equivalent shear work that extends obliquely from high rotation speed / short time to medium rotation speed / medium time. Within this zone, the CV value can be reduced to below 5%.

[0106] However, this equivalent shear strength band is not usable along its entirety. As the stirring motion inevitably crosses the system's gelation critical point, the high-speed impellers sever the nascent polyurethane network. This is clearly demonstrated by the data surface of room-temperature tear strength, where the absolute peak value falls around (3000 rpm, 6 s). Once the stirring time exceeds 8 seconds, the tear strength drops drastically regardless of the rpm.

[0107] In the low to medium speed range, the density change is relatively gradual; however, after entering the high speed range for a long time, due to the extremely violent cavitation and shearing effects, the initial bubble nuclei are broken up over a large area and the gas is forcibly thrown out of the liquid surface, causing the foaming expansion to completely fail, and the apparent density soars to 5 to 8 times the normal value in a parabolic manner, forming a solid dead skin.

[0108] To ensure extreme microscopic homogeneity (low CV value) while maximizing the preservation of skeletal toughness (high tear strength) and air cell expansion force (low density), this experiment performed spatial overlap and simultaneous optimization calculations on the three fitted surfaces mentioned above. When the stirring speed was set to 2850 r / min and the impact mixing time was controlled at 5.8 seconds, the system achieved optimal dispersion just before the skeletal structure was cut. Considering the established speed settings of industrial equipment and the tolerance of the timer, this experiment ultimately selected a stirring speed of 3000 r / min and a mixing time of 6 seconds as the optimal high-speed impact mixing process parameters for the mass production of the foaming system.

[0109] 3.4 In-mold curing and post-curing annealing process The foaming liquid, which has been mixed at high speed under the optimal parameters (3000r / min, 6 seconds), is rapidly injected into a car armrest mold that has been pre-coated with a release agent and preheated to 55~70℃ within 2 seconds. The mold is then immediately closed and left to stand and mature for 8~12 minutes.

[0110] Ten minutes later, open the mold and carefully remove the molded foamed part. Because the vigorous foaming process leaves significant mechanical and thermal stresses within the polymer network, direct use at this point can easily lead to misalignment or lag in the shape memory network. The freshly demolded semi-finished foamed part must be immediately placed in a constant temperature oven set at 70-90℃ for 3-5 hours of post-curing annealing.

[0111] During this annealing process, the residual stress within the polyurethane matrix is ​​fully released, while the hard segment microphase separation region (crystalline region) and the isocyanate-based silane-modified nanocrystalline cellulose crosslinking anchor points complete the final physical rearrangement and thorough fixation. After annealing and natural cooling to room temperature, an extremely stable and highly ordered anti-slip three-dimensional network is formed inside the automotive armrest foam component, exhibiting excellent compressive support and shape memory function that actively recovers from pressure collapse under heated conditions inside the vehicle. Example 4

[0112] Reference Figure 6 This is the fourth embodiment of the present invention. This embodiment provides a method for preparing a foamed component to prevent collapse for automotive armrests. The specific preparation process is as follows: 100 parts by weight of polytetrahydrofuran ether diol were added to a large-capacity, jacketed, temperature-controlled reactor and heated to 80°C until completely melted into a liquid state. Then, 3 parts by weight of isocyanate-modified silane nanocrystalline cellulose were added to the reactor. A mechanical stirrer was started and maintained at 800 rpm. The reactor was continuously vacuum-dehydrated for 2 hours to ensure uniform dispersion of the nanofiller under strong shear force and to prevent residual moisture in the system, thus forming a mixed pre-prepared base liquid.

[0113] After dehydration, the vacuum in the reactor was released and dry nitrogen was introduced for protection. The reactor temperature was steadily lowered to 70°C, and then 50 parts by mass of diphenylmethane diisocyanate were added dropwise to the mixed pre-prepared base solution at a uniform rate using a precision metering pump, with the addition time strictly controlled at 30 minutes. After the addition was complete, the reaction was continued at a constant temperature of 70°C and 800 rpm for 2 hours with stirring, to synthesize a prepolymer with isocyanate end groups on the molecular chain and modified microcrystalline cellulose uniformly suspended inside. The prepolymer was then allowed to cool naturally to 40°C, stirring was stopped, and the mixture was sealed for later use.

[0114] In a dedicated mixing container, 7.5 parts by weight of 1,4-butanediol, 2.5 parts by weight of deionized water, 3.5 parts by weight of polysiloxane-polyoxyethylene ether copolymer, 0.3 parts by weight of 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine (foaming gas-generating catalyst) and 0.35 parts by weight of zirconium acetylacetonate (skeletal crosslinking catalyst) are thoroughly mixed to prepare a homogeneous mixed additive.

[0115] Subsequently, the high-speed stirring device of the reactor containing the prepolymer is turned on. When the speed is steadily increased to 3000 rpm, the prepared mixing agent is quickly poured into the prepolymer in one go and subjected to high-speed impact mixing for only 6 seconds, so that all components are thoroughly dispersed without damaging the nascent reaction network.

[0116] After a 6-second mixing process, the milky-white foamed mixture is injected into a pre-coated, preheated (60°C) automotive armrest mold within 2 seconds, followed by immediate mold closing. The foamed liquid undergoes free expansion and cross-linking within the mold, and is allowed to stand for 10 minutes to mature. The mold is then opened, the semi-finished foamed part is removed, and immediately placed in an 80°C constant-temperature oven for a 4-hour post-maturation annealing process. After annealing, the foamed part is allowed to cool naturally to room temperature, completely releasing internal stress and thoroughly fixing the shape memory microphase network, resulting in the final automotive armrest foamed part.

[0117] Testing revealed that the finished foamed parts exhibited a 25% indentation hardness of 142.5 N at room temperature, with a moderately soft and supple feel, fully meeting the comfort and cushioning standards required for automotive interior ergonomics. The foam structure displayed a uniform semi-open-cell state, with a closed-cell rate of 18.6%, and the density gradient difference between the core and the surface was only 5.2 kg / m³. 3 The interior has no macroscopic voids or dense dead skin layers. The room temperature tear strength is 3.85 N / mm; after 80,000 constant load dynamic fatigue compression impacts, its residual deformation rate is 1.82%. After applying heavy pressure to the finished product to induce ultimate residual deformation, it is placed in an environment of 45℃ to simulate the summer temperature rise inside a car, and its thermally induced shape memory recovery rate is 98.2%.

[0118] In summary, this invention utilizes polytetrahydrofuran ether diol and a specific chain extender to construct a polyurethane shape memory matrix, and introduces nanocrystalline cellulose modified by isocyanate-based silane coupling. The modified nanocrystalline cellulose can be uniformly dispersed and anchored in the polymer cross-linked network, hindering the slippage of molecular chains under long-term pressure, thereby endowing the foamed component with dynamic fatigue resistance. The foaming system possesses thermo-induced shape memory function. After residual deformation occurs due to long-term pressure, triggered by the temperature rise caused by the vehicle interior environment or human body temperature, the internal hard segment micro-regions can unbundle and drive the foamed component to actively return to its initial shape, achieving long-term anti-collapse support while maintaining the soft and cushioning feel of the foam material.

[0119] By balancing the kinetic rates of foaming gas generation and skeleton gelation reactions using a dual-catalyst system, and with optimized high-speed impact mixing parameters, the foaming liquid maintains a stable rheological state during mold filling. This effectively avoids structural defects such as macroscopic bubble collapse, closed-cell shrinkage, and severe density delamination between the core and skin caused by reaction out-of-step, ensuring the consistency of cell size and density uniformity within the foamed part. Optimized stirring and curing processes enable the modified nanofiller to be fully dispersed without damaging the nascent polyurethane network, further improving the overall tear resistance and production stability of the finished product, meeting the needs of large-scale injection molding.

[0120] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a foamed component for preventing collapse in automotive armrests, characterized in that... Includes the following steps: S1. Place 80-120 parts by weight of polytetrahydrofuran ether diol into a reactor and heat to melt. Then add 2-4 parts by weight of modified nanocrystalline cellulose and dehydrate under vacuum to form a mixed pre-prepared base liquid. S2. Nitrogen gas is introduced into the reaction vessel, and 40-60 parts by mass of diphenylmethane diisocyanate are added dropwise to the mixed pre-prepared base liquid at a uniform rate. After the addition is completed, the mixture is stirred at a constant temperature to fully react and synthesize a prepolymer with isocyanate end groups on the molecular chain and containing uniform microcrystalline cellulose. S3. Mix 5-10 parts by weight of 1,4-butanediol, deionized water, 2-5 parts by weight of polysiloxane-polyoxyethylene ether copolymer, 0.1-0.5 parts by weight of 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine and 0.1-0.5 parts by weight of zirconium acetylacetonate evenly to prepare a mixed additive. S4. Start the high-speed stirring device and quickly add the mixing aid to the prepolymer, and mix at high speed of 2000~4000 rpm for 4~8 seconds. S5. After mixing, quickly inject the foaming mixture into the preheated mold and close the mold. After curing, open the mold and take out the molded foamed part. Perform curing annealing treatment on the molded foamed part and then let it cool naturally to room temperature to obtain a car armrest foamed part with shape memory function.

2. The method for preparing anti-collapse foamed parts for automobile armrests according to claim 1, characterized in that, In step S1, the amount of polytetrahydrofuran ether diol added is 100 parts, the amount of modified nanocrystalline cellulose added is 3 parts, and the modifier used for the modified nanocrystalline cellulose is isocyanate-based silane.

3. The method for preparing anti-collapse foamed parts for automobile armrests according to claim 1, characterized in that, In step S2, the amount of diphenylmethane diisocyanate added is 50 parts.

4. The method for preparing anti-collapse foamed parts for automobile armrests according to claim 1, characterized in that, In step S3, the amount of 1,4-butanediol added is 7.5 parts, the amount of deionized water added is 1.5 to 3.5 parts, the amount of polysiloxane-polyoxyethylene ether copolymer added is 3.5 parts, the amount of 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine added is 0.3 parts, and the amount of zirconium acetylacetonate added is 0.35 parts.

5. The method for preparing anti-collapse foamed parts for automobile armrests according to claim 1, characterized in that, In step S4, the high-speed impact mixing parameter is 3000 rpm for 6 seconds.

6. The method for preparing anti-collapse foamed parts for automobile armrests according to claim 1, characterized in that, In step S1, the temperature of the reactor is maintained at 70~90℃, and the reactor is continuously stirred at a speed of 700~900rpm for 1~3h during the dehydration process.

7. The method for preparing anti-collapse foamed parts for automobile armrests according to claim 6, characterized in that, In step S2, the rotation speed is maintained at 700~900 rpm. After dehydration is completed, the temperature of the reactor is adjusted to 60~80℃. The uniform dripping time is controlled at 20~40 min. After the dripping is completed, the reactor is stirred for 1~3 h. Then it is allowed to cool naturally to 35~45℃. Stirring is stopped and the reactor is sealed for later use.

8. The method for preparing anti-collapse foamed parts for automobile armrests according to claim 1, characterized in that, In step S5, the injection process into the mold is controlled within 2 seconds, the preheating temperature of the mold is 55~70℃, and the curing time is 8~12 minutes.

9. The method for preparing anti-collapse foamed parts for automobile armrests according to claim 1, characterized in that, In step S5, the molded foamed part is annealed at 70~90℃ for 3~5 hours.

10. A foam component for preventing collapse in car armrests, characterized in that, Prepared by any one of claims 1 to 9, the microstructure of the foamed part includes a shape memory cross-linked network composed of alternating flexible polyether soft segments and rigid polyurethane hard segments, wherein the isocyanate-based silane modified nanocrystalline cellulose is uniformly embedded in the shape memory cross-linked network, serving as a physical anchoring node and interpenetrating with the polyurethane macromolecular chain to form a three-dimensional fatigue-resistant skeleton that impedes the slippage of the molecular chain under pressure.

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