Low-carbon TPO material and preparation method thereof

Abstract

The invention relates to the technical field of polymer composite materials, and discloses a low-carbon TPO (thermoplastic polyolefin) material which comprises the following components in parts by mass: 45-55 parts of bio-based polypropylene; 25 to 35 parts of regenerated TPO particles; 15 to 25 parts of bamboo fiber; 0.5 to 2.0 parts of a dynamic covalent cross-linking agent; 2-4 parts of a supercritical fluid foaming agent; the low-carbon TPO material is composed of a three-layer composite structure, and the three-layer composite structure comprises a surface layer which is a compact layer composed of bio-based polypropylene and nano silicon dioxide; the middle layer is a foaming layer containing a dynamic cross-linked network; and the bottom layer is a bamboo fiber reinforced layer. Through reversible cross-linked network design of dynamic covalent bonds, the material can autonomously reconstruct a cross-linked structure in multiple melting processing processes, and the technical problem that a traditional thermosetting material such as an electronic cross-linked TPO material cannot be recycled is solved. The integrity of molecular chains is kept during cyclic regeneration of the material, performance degradation is avoided, and resource consumption and waste discharge are remarkably reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer composite materials, in particular to a low-carbon TPO material and a preparation method thereof. BACKGROUND

[0002] In the process of pursuing lightweight and low carbonization, traditional polyolefin materials have long faced irreconcilable contradictions. The widespread use of petroleum-based raw materials leads to high carbon footprint, while the introduction of biomass fillers often accompanies poor interfacial compatibility, sudden drop in mechanical properties and other problems, which are difficult to meet the stringent requirements of high value-added application scenarios on the comprehensive performance of materials.

[0003] Existing foaming technologies mostly rely on physical or chemical foaming agents, the decomposition residues of which not only pollute the environment, but also damage the integrity of the cell structure, causing a vicious imbalance between material density and strength. More seriously, the irreversible nature of traditional crosslinking modification seriously hinders material recycling, and a large amount of waste is treated by incineration or landfill, which is contrary to the global carbon neutralization goal.

[0004] At the processing level, a single temperature field control strategy is difficult to coordinate the dynamic matching of melt rheological behavior and foaming kinetics, resulting in frequent defects such as cell collapse and fiber orientation disorder during complex structure molding, which seriously restricts the realization of precision manufacturing. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a low-carbon TPO material and a preparation method thereof, which solves the problems of non-recyclable traditional electronic crosslinking polyolefin materials, weak interfacial bonding between biomass fillers and matrix, uncontrollable foaming structure and poor adaptability of complex molding processing.

[0006] To achieve the above purpose, the present application is realized by the following technical scheme: The first aspect of the present application provides a low-carbon TPO material, which comprises the following components by mass fraction: Bio-based polypropylene: 45-55 parts; Recycled TPO particles: 25-35 parts; Bamboo fibers: 15-25 parts; Dynamic covalent crosslinking agent: 0.5-2.0 parts; Supercritical fluid foaming agent: 2-4 parts; Nano-silicon dioxide: 2-5 parts.

[0007] Preferably, the low-carbon TPO material is composed of a three-layer composite structure, and the three-layer composite structure comprises: Surface layer: a dense layer composed of bio-based polypropylene and nano-silicon dioxide; Intermediate layer: a foaming layer containing a dynamic crosslinking network; The bottom layer is a bamboo fiber reinforced layer.

[0008] Preferably, the thickness of the three-layer composite structure is respectively: The surface layer is 0.1-0.2mm; The middle layer is 0.2-0.5mm; The bottom layer is 0.2-0.5mm.

[0009] Preferably, the bamboo fiber is a double-modified bamboo fiber with surface grafting of silane coupling agent and maleic anhydride, and the grafting rate is 85-95%.

[0010] Preferably, the supercritical fluid foaming agent is supercritical CO2.

[0011] The second aspect of the present application provides a preparation method of the low-carbon TPO material of the first aspect of the present application, comprising the following steps: S1, pretreating the bio-based polypropylene, recycled TPO particles and bamboo fiber to obtain compatible raw materials; S2, melt blending the pretreated raw materials with a dynamic covalent crosslinking agent and a supercritical fluid foaming agent to form a dynamic crosslinked TPO matrix; S3, processing the dynamic crosslinked TPO matrix into a three-layer composite structure blank through a multi-layer co-extrusion foaming process; S4, heat pressing and crosslinking the blank to activate the dynamic covalent bond network; S5, surface functionalization treatment of the crosslinked material to obtain the low-carbon TPO material.

[0012] Preferably, the step S1 comprises: Bio-based polypropylene is vacuum dried at 80-85℃ for 3-4 hours; Recycled TPO particles are blended and granulated with maleic anhydride grafted polypropylene at a mass ratio of 95:5; The bamboo fiber is double-grafted and modified by silane coupling agent KH550 and maleic anhydride.

[0013] Preferably, the temperature control of the layer co-extrusion in the step S3 is: The surface layer extrusion temperature is 180-220℃; The middle layer extrusion temperature is 160-210℃; The bottom layer extrusion temperature is 170-210℃.

[0014] Preferably, the conditions of heat pressing and dynamic crosslinking in the step S4 are: The temperature is 120-130℃; The pressure is 7-10MPa; The pressure holding time is 4-6 minutes.

[0015] Preferably, the surface functionalization treatment in step S5 includes: Apply a water-based acrylic-silicone hybrid coating that cures to form an abrasion-resistant coating; The imitation leather texture is formed on the surface through the embossing process.

[0016] The present invention provides a low-carbon TPO material and a preparation method thereof, which has the following beneficial effects: 1. This invention utilizes a reversible crosslinking network design based on dynamic covalent bonds. The material can autonomously restructure its crosslinking structure during multiple melt processing cycles, overcoming the technical limitations of conventional electronically crosslinked thermosetting polyolefin (TPO) materials, which are non-recyclable. This allows the material to maintain molecular chain integrity during recycling, preventing performance degradation and significantly reducing resource consumption and waste emissions.

[0017] 2. This invention utilizes the synergistic innovation of directional biomass fiber reinforcement and supercritical foaming technology to create a "honeycomb skeleton-fiber support" composite structure within the material. The biomass fibers form a three-dimensional reinforcement network within the foamed matrix, effectively dispersing external loads. Simultaneously, the uniform closed-cell structure created by supercritical foaming significantly reduces weight, achieving a synergistic improvement in both lightweighting and mechanical properties, resolving the problem of traditional materials experiencing a sudden drop in strength associated with lightweighting.

[0018] 3. The dual-grafting modification technology of this invention achieves a cross-scale interface fusion between the biomass fiber and the polyolefin matrix through the dual effects of chemical bond bridging and physical entanglement. Chemical bonding resists interfacial stress erosion in hot and humid environments, while the physical interlocking structure inhibits microcrack propagation, enabling the material to maintain stable interfacial bonding strength under complex working conditions, thus overcoming the core technical issues of biomass fillers' susceptibility to moisture absorption and debonding.

[0019] 4. This invention utilizes a multi-layer co-extrusion temperature gradient strategy to precisely control the viscoelastic behavior of different melt layers, achieving dynamic matching between foaming dynamics and molding process. This avoids cell rupture and fiber orientation disturbance caused by insufficient melt strength during the molding of thin-walled or special-shaped structures, thereby improving the yield rate of complex parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a flow chart of the preparation method of the present invention. DETAILED DESCRIPTION

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0022] Please see the attachedFigure 1 The low-carbon TPO material provided by the application takes bio-based polypropylene, recycled TPO particles, and bamboo fibers as core components, combines dynamic covalent cross-linking agents with supercritical fluid foaming agents, and forms a multi-layer composite structure with recyclability, lightweight, and high performance. The following technical features realize material low carbonization and functionalization: Synergistic use of bio-based polypropylene (45-55 parts) and recycled TPO particles (25-35 parts) Bio-based polypropylene is derived from renewable resources (such as vegetable oil), and its molecular chain structure is consistent with that of petroleum-based polypropylene, but its carbon footprint is significantly reduced. Recycled TPO particles (post-consumer waste) are blended with bio-based polypropylene through pretreatment, which not only reduces raw material consumption, but also avoids environmental pollution of waste TPO. Both are compatibilized by maleic anhydride grafted polypropylene to form a compatible interface, solving the problem of phase separation caused by the polarity difference between bio-based and recycled materials.

[0023] Double graft modification of bamboo fibers (15-25 parts) After the double graft modification of bamboo fibers with silane coupling agent (KH550) and maleic anhydride, the surface hydroxyl groups are replaced by hydrophobic groups, improving the interfacial bonding force with the polyolefin matrix. At the same time, the grafted maleic anhydride can react with the polypropylene chain to enhance the mechanical interlocking between the fiber and the matrix, avoiding the mechanical property decline caused by the weak interface of traditional fillers.

[0024] Reversible network construction of dynamic covalent cross-linking agent (0.5-2.0 parts) Furan-maleimide (F-MI) dynamic covalent cross-linking agent forms a reversible cross-linking network through Diels-Alder reaction. During the material use stage (<80℃), the cross-linking network provides stable mechanical support; during the recycling stage (>120℃), the cross-linking bond dissociates, and the material can be reprocessed. This dynamic cross-linking mechanism breaks through the irreversible degradation problem caused by sulfide or peroxide cross-linking in traditional TPO materials, realizing multiple recycling.

[0025] Combination of supercritical CO2 foaming agent (2-4 parts) and layered co-extrusion process Supercritical CO2 is injected into the TPO matrix during melt blending, and uniform microporous structure is formed by rapid pressure relief. In the layered co-extrusion process, the surface layer is extruded at high temperature (180-220℃) to form a dense layer (containing 5-10% nano-silicon dioxide), the middle layer is extruded at low temperature (160-210℃) to retain the foaming structure, and the bottom layer is extruded at medium temperature (170-210℃) to realize the dispersion and interface fusion of bamboo fibers. The temperature gradient design ensures that the foaming layer completes the pore structure shaping before cross-linking, avoiding melt collapse.

[0026] Three-layer composite structure The surface dense layer (biobased PP + nano-SiO2) provides wear resistance and surface hardness; the middle foaming layer (dynamic crosslinking TPO matrix) realizes lightweight and cushioning performance; the bottom layer of bamboo fiber reinforced layer improves impact resistance and dimensional stability. The full TPO material design (without polyester or metal composite) makes it unnecessary to sort when recycling, and directly crushes, melts and granulates, simplifying the recycling process and reducing energy consumption.

[0027] The application provides a preparation method of the low-carbon TPO material, and comprises the following steps: S1, pretreating biobased polypropylene, recycled TPO particles and bamboo fibers to obtain compatible raw materials; The biobased polypropylene is dried by vacuum drying to avoid hydrolytic degradation during processing; the recycled TPO particles are blended and granulated with maleic anhydride grafted PP to repair the molecular chain breakage caused by repeated processing and introduce polar groups to improve the interfacial bonding; the bamboo fiber is double-grafted and modified to enhance the compatibility with the matrix through the dual action of chemical bonds and physical entanglement.

[0028] S2, melt blending the pretreated raw materials with a dynamic covalent crosslinking agent and a supercritical fluid foaming agent to form a dynamic crosslinking TPO matrix; The dynamic crosslinking agent (F-MI) is injected in the late stage (4 zone) of melt blending to avoid premature crosslinking at high temperature. After the supercritical CO2 is injected in zone 2, a homogeneous system is formed by screw shearing dispersion, and the time sequence separation of the foaming agent and the crosslinking agent solves the contradictory requirements of the foaming process on the melt strength (low melt strength is required for foaming, and high melt strength is required for crosslinking).

[0029] S3, processing the dynamic crosslinking TPO matrix into a three-layer composite structure blank through a multi-layer co-extrusion foaming process; the three-layer co-extrusion synchronously forms a three-layer structure through three independent temperature-controlled extruders. High-temperature extrusion of the surface layer ensures rapid cooling and setting of the dense layer; low-temperature extrusion of the middle layer retains the foaming structure; and medium-temperature extrusion of the bottom layer balances the fiber dispersion and melt flowability.

[0030] S4, hot-pressing crosslinking of the blank to activate the dynamic covalent bond network; The hot-pressing crosslinking stage (120-130℃ / 7-10MPa) activates the dynamic covalent bond reorganization, so that the foaming layer microcellular structure and the interfaces of each layer are fixed through the crosslinking network, avoiding structure relaxation in subsequent use. The water-based acrylic-silicone hybrid coating forms a wear-resistant coating on the surface layer through a roll coating process, and its curing process (80-85℃) will not damage the dynamic crosslinking network.

[0031] S5, surface functionalization treatment of the crosslinked material to obtain a low-carbon TPO material.

[0032] Waterborne acrylic-silicone hybrid coating forms a wear-resistant coating on the surface layer through a roll coating process, and its curing process (80-85°C) does not destroy the dynamic crosslinking network. The imitation leather texture embossing process (110-120°C / 2-4MPa) forms a micro concave-convex structure on the surface of the material, improves the touch and aesthetics, and at the same time avoids the deformation of the matrix caused by high temperature and high pressure.

[0033] In order to better understand the present application, the present application is described in detail below in combination with specific examples.

[0034] Example 1: Raw material ratio Bio-based polypropylene: 55 parts Recycled TPO particles: 35 parts Bamboo fiber: 25 parts Dynamic covalent crosslinking agent (F-MI): 2.0 parts Supercritical CO2 foaming agent: 4 parts Nano-silicon dioxide: 5 parts.

[0035] Preparation steps S1, raw material pretreatment Bio-based PP treatment: Bio-based PP particles were dried at 85°C under -0.1MPa vacuum for 4 hours, water content ≤0.03%.

[0036] Recycled TPO treatment: Recycled TPO fragments were blended with 5% maleic anhydride grafted PP, and twin-screw granulation was carried out at 185°C and 200rpm.

[0037] Bamboo fiber modification: Bamboo fiber was immersed in a 5% KH550 and 2% maleic anhydride ethanol solution, ultrasonically treated at 60°C for 30 minutes, and dried at 105°C for 1.5 hours.

[0038] S2, preparation of dynamic crosslinked matrix The pretreated raw materials were mixed with F-MI crosslinking agent and nano-SiO2, and fed into a twin-screw extruder (L / D=40:1).

[0039] Segmented temperature control: 1 zone 160°C, 2 zone 170°C, 3 zone 175°C, 4 zone 170°C, 5 zone 165°C.

[0040] Foaming agent injection: Supercritical CO2 was injected at 2 zone at 10MPa, 1.0L / min.

[0041] Crosslinking agent injection: F-MI was added at 4 zone at 1.5kg / h.

[0042] S3, layered co-extrusion foaming surface layer: bio-based PP + 5 parts of nano-SiO2, extrusion temperature 220°C, screw speed 40rpm, die pressure 10MPa.

[0043] Middle layer: dynamically crosslinked matrix, extrusion temperature 210℃, screw rotation speed 50rpm, die pressure 7MPa.

[0044] Bottom layer: dynamically crosslinked matrix + 25 parts of bamboo fiber, extrusion temperature 210℃, screw rotation speed 45rpm, die pressure 9MPa.

[0045] S4, hot-press crosslinking Hot-press temperature 130℃, pressure 10MPa, pressure holding time 6 minutes, cooling rate 15℃ / min to 50℃ demolding.

[0046] S5, surface treatment Coating water-based acrylic-silicone paint (solid content 45%), coating speed 3m / min, 85℃ curing for 10 minutes.

[0047] Embossing temperature 120℃, pressure 4MPa, time 30 seconds, forming Ra=10μm imitation leather texture.

[0048] Example 2: Raw material ratio: Bio-based polypropylene: 50 parts Recycled TPO particles: 30 parts Bamboo fiber: 20 parts Dynamic covalent crosslinking agent (F-MI): 1.2 parts Supercritical CO2 foaming agent: 3 parts Nano-silicon dioxide: 3.5 parts.

[0049] Preparation steps S1, raw material pretreatment Bio-based PP treatment: 82℃, -0.09MPa vacuum drying for 3.5 hours, water content ≤0.02%.

[0050] Recycled TPO treatment: recycled TPO was blended with 5% maleic anhydride grafted PP and granulated at 175℃, 175rpm.

[0051] Bamboo fiber modification: bamboo fiber was immersed in a 4% KH550 and 1.5% maleic anhydride solution, ultrasonically treated at 58℃ for 28 minutes, and dried at 102℃ for 1.2 hours.

[0052] S2, dynamically crosslinked matrix preparation Temperature control by segmented twin-screw extruder: zone 1 158℃, zone 2 168℃, zone 3 172℃, zone 4 168℃, zone 5 163℃.

[0053] Foaming agent injection: CO2 was injected at 2 zone at 9MPa, 0.8L / min.

[0054] Crosslinker injection: F-MI was added at 4 zone with 1.0 kg / h.

[0055] S3, Layered co-extrusion foamed skin: Bio-based PP + 3.5 parts of nano-SiO2, extrusion temperature 185°C, screw speed 35 rpm, die pressure 9 MPa.

[0056] Middle layer: dynamically crosslinked matrix, extrusion temperature 165°C, screw speed 45 rpm, die pressure 6 MPa.

[0057] Bottom layer: dynamically crosslinked matrix + 20 parts of bamboo fiber, extrusion temperature 175°C, screw speed 40 rpm, die pressure 8 MPa.

[0058] S4, Hot-pressing crosslinking Hot-pressing temperature 125°C, pressure 8 MPa, holding time 5 minutes, cooling rate 12°C / min to 50°C demolding.

[0059] S5, Surface treatment Coating speed 2.5 m / min, curing at 83°C for 9 minutes, embossing pressure 3 MPa, time 25 seconds, Ra = 8 μm.

[0060] Example 3: Raw material ratio Bio-based polypropylene: 45 parts Recycled TPO particles: 25 parts Bamboo fiber: 15 parts Dynamic covalent crosslinker (F-MI): 0.5 parts Supercritical CO2 foaming agent: 2 parts Nano-silica: 2 parts Preparation steps S1, Raw material pretreatment Bio-based PP treatment: 80°C, -0.08 MPa vacuum drying for 3 hours, water content ≤0.02%.

[0061] Recycled TPO treatment: Recycled TPO was blended with 5% maleic anhydride grafted PP and granulated at 170°C, 150 rpm.

[0062] Bamboo fiber modification: Bamboo fiber was immersed in a 3% KH550 and 1% maleic anhydride solution, ultrasonically treated at 55°C for 25 minutes, and dried at 100°C for 1 hour.

[0063] S2, Preparation of dynamically crosslinked matrix Temperature control by segmented twin-screw extruder: Zone 1 155°C, Zone 2 165°C, Zone 3 170°C, Zone 4 165°C, Zone 5 160°C.

[0064] Foaming agent injection: CO2 was injected at 8 MPa, 0.5 L / min in zone 2.

[0065] Crosslinking agent injection: F-MI was added at 0.5 kg / h in zone 4.

[0066] S3, Layered co-extrusion foaming skin layer: Bio-based PP + 2 parts of nano-SiO2, extrusion temperature 180℃, screw rotation speed 30 rpm, die pressure 8 MPa.

[0067] Middle layer: dynamically crosslinked matrix, extrusion temperature 160℃, screw rotation speed 40 rpm, die pressure 5 MPa.

[0068] Bottom layer: dynamically crosslinked matrix + 15 parts of bamboo fiber, extrusion temperature 170℃, screw rotation speed 35 rpm, die pressure 7 MPa.

[0069] S4, Hot-pressing crosslinking Hot-pressing temperature 120℃, pressure 7 MPa, pressure holding time 4 minutes, cooling rate 10℃ / min to 50℃ demolding.

[0070] S5, Surface treatment Coating speed 2 m / min, curing at 80℃ for 8 minutes, embossing pressure 2 MPa, time 20 seconds, Ra = 5 μm.

[0071] Comparative Example 1: Compared with Example 1, the difference is that no dynamic covalent crosslinking agent (F-MI) is added, and the rest of the components and process parameters are the same.

[0072] Comparative Example 2: Compared with Example 1, the difference is that the dynamic covalent crosslinking agent (F-MI) is replaced with an equal amount of traditional dicumyl peroxide (DCP), and the rest of the components and process parameters are the same.

[0073] Comparative Example 3: Compared with Example 2, the difference is that the bamboo fiber is not modified by silane coupling agent and maleic anhydride double grafting, and the untreated bamboo fiber is directly used, and the rest of the components and process parameters are the same.

[0074] Comparative Example 4: Compared with Example 2, the difference is that the layered co-extrusion temperature gradient control is cancelled, and the three layers all use a unified extrusion temperature of 175℃, and the rest of the components and process parameters are the same.

[0075] Comparative Example 5: Compared with Example 3, the difference is that the supercritical CO2 foaming agent is replaced with an equal amount of physical foaming agent (azodicarbonamide), and the rest of the components and process parameters are the same.

[0076] Comparative Example 6: Comparative Example 6:

[0077] Test Example 1: Effect of dynamic crosslinker on recyclability Experimental procedure Sample preparation Example 1: Prepare low carbon TPO material with maximum ratio according to claim 1; Comparative Example 1: Same as Example 1, but without adding dynamic crosslinker (F-MI); Comparative Example 2: Same as Example 1, but replace F-MI with equal amount of traditional crosslinker DCP.

[0078] Decrosslinking and recycling process Crush each sample into 2-4mm particle size; Use a flat vulcanizing machine, set temperature 120℃, pressure 0.5MPa, hot-press for 15 minutes; Observe whether the material recovers processability (whether a uniform melt is formed).

[0079] Recycled material injection molding Put the decrosslinked material into the injection molding machine (cylinder temperature 180℃, mold temperature 40℃); Prepare standard tensile bars (ASTM D638 Type I).

[0080] Mechanical property test Use a universal testing machine (tensile rate 50mm / min) to test the tensile strength of the recycled material; Calculate the tensile strength retention rate (recycled material strength / original material strength x 100%).

[0081] The experimental results are shown in Table 1: Table 1: Effect of dynamic crosslinker on material recyclability test data Group Whether re-granulation is possible Tensile strength of recycled material (MPa) Tensile strength retention rate (%) Example 1 Yes 32.7 93.5 Comparative Example 1 No 16.8 (surface bubbles) 48 Comparative Example 2 Partly granulated 22.1 (poor flowability) 63.1 From the experimental results in Table 1, we can get: The introduction of dynamic covalent crosslinking system is the core of the material to realize efficient recycling and performance retention. In the decrosslinking recycling process, the furan-maleimide (F-MI) dynamic crosslinking network undergoes bond rupture through Diels-Alder reversible reaction under the condition of 120℃ hot-pressing, so that the molecular chain is stretched again after melting, and the crosslinking network reversibly reorganizes after cooling. This mechanism avoids the problem of irreversible covalent bond rupture of traditional peroxide crosslinking (such as DCP), which leads to molecular chain degradation due to free radical attack during decrosslinking, and the mechanical properties of the recycled material are significantly deteriorated.

[0082] The results of Comparative Example 1 (without crosslinking agent) further verify the necessity of the dynamic crosslinking network: the uncrosslinked material collapses the pore structure due to the lack of stable three-dimensional network support when the foamed layer is melted and regenerated, resulting in the loss of mechanical properties. The dynamic crosslinking network provides both melt flowability and retains the matrix continuity through bond reorganization during the decrosslinking process, enabling the regenerated material to reproduce more than 85% of the original structure performance.

[0083] The dynamic crosslinking technology of the present application breaks through the limitations of traditional TPO materials "one-time use", and realizes low-carbon recycling of the whole life cycle of the material through reversible bond design at the molecular level. Compared with physical blending or irreversible crosslinking system, this technology reduces the energy consumption of the regeneration process to less than 30% of the traditional pyrolysis method, while avoiding secondary pollution from solvent recovery, providing a new path for green manufacturing of polymer materials.

[0084] Test Example 2: Effect of Bamboo Fiber Modification on Interface and Mechanical Properties Experimental steps Sample preparation Example 2: Prepare low-carbon TPO material according to the intermediate ratio in the claim, and use double-graft modified bamboo fiber; Comparative Example 3: The same as Example 2, but using unmodified bamboo fiber.

[0085] Interface bonding force test After the material is brittle fractured by liquid nitrogen, it is gold sprayed, and the interface morphology of the bamboo fiber and the matrix is observed under 5000 times by scanning electron microscope (SEM); According to the gap width and debonding area of the fiber and the matrix in the SEM image, the interface bonding grade is divided (1-5 grades, 1 grade is the worst, and 5 grade is the best).

[0086] Impact strength test Cut the material into 80x10x4mm 3 Notched sample (notch depth 2mm); Use a cantilever beam impact testing machine (pendulum energy 5.5J) to test the notched impact strength, and repeat 5 times for each group.

[0087] The experimental results are shown in Table 2: Table 2 Test data of the effect of bamboo fiber modification on interface and impact strength Group Interfacial bonding level impact strength (kJ / m 2 ) SEM typical morphology description Example 2 4.8 25.3 Fiber surface is coated and dense, no cracks Comparative Example 3 1.6 14.8 Fiber is exposed, crack > 50 μm From the experimental results in Table 2, we can get: The double grafting modification of bamboo fiber forms a strong interface with the matrix through surface chemical modification, which is the key to achieving high impact resistance of the material. The silanol groups generated by the hydrolysis of silane coupling agent (KH550) condense with the hydroxyl groups on the surface of bamboo fiber, forming stable Si—O—C bonds, which makes the fiber surface change from hydrophilic to hydrophobic, reducing the polarity difference with the polyolefin matrix. At the same time, the anhydride groups of maleic anhydride react with the hydroxyl groups at the end of the polypropylene molecular chain during melt blending, building a chemical bond bridge at the fiber-matrix interface, significantly improving the stress transfer efficiency. The physical-chemical synergistic effect makes it difficult for cracks to propagate along the interface under impact load, thereby avoiding the early fracture caused by interface debonding of traditional unmodified fibers.

[0088] Experimental data show that there is a clear micron-level crack (SEM observation > 50 μm) between the unmodified bamboo fiber and the matrix, which becomes a stress concentration point under impact load, and the crack rapidly expands, resulting in a decrease in impact strength of more than 50%. The double grafting modified fiber disperses impact energy to the entire matrix through dense interface coating and chemical bonding, allowing the material to absorb more energy before failure. This interface strengthening mechanism not only improves the mechanical properties, but also ensures that the bamboo fiber remains stably bonded with the matrix during multiple processing cycles, avoiding performance degradation of the recycled material due to fiber-matrix peeling.

[0089] The bamboo fiber modification strategy of the present application breaks through the technical bottleneck of poor compatibility between natural fibers and polyolefins, and through molecular-level interface design, the reinforcing efficiency of biomass fillers in the polymer matrix reaches more than 70% of that of traditional glass fibers, while avoiding the pollution of glass fibers to the recycling process. Compared with single modification (such as only silane coupling or maleic anhydride grafting), the synergistic effect of double grafting additionally improves the impact strength by 30-40%, providing a reliable solution for low-cost, high-mechanical-property low-carbon composites.

[0090] Test Example 3: Effect of Layered Co-extrusion Temperature Gradient on Foaming Structure Experimental Steps Sample Preparation Examples 1-3: Low-carbon TPO materials were prepared according to the maximum, intermediate, and minimum component allocation ratios, respectively, and a layered co-extrusion temperature gradient was used; Comparative Example 4: The same components as Example 2, but the three-layer co-extrusion temperature was uniformly 175°C.

[0091] Micro-CT Scanning of Foaming Layer The foaming area of the middle layer of the cut material (5×5×5mm 3 ) was scanned using a micro-CT (resolution 1 μm); Ten areas were randomly selected, and the pore size distribution (average pore size and standard deviation) was measured.

[0092] Apparent Density Test According to ASTM D792 standard, the density of the foamed area of ​​the middle layer was measured using the drainage method; Five parallel samples were taken from each group, and the mean and range of the density were calculated.

[0093] The experimental results are shown in Table 3: Table 3 Test data on the effect of layered co-extrusion temperature gradient on foaming structure From the experimental results in Table 3, we can get: The design of the layered co-extrusion temperature gradient achieves directional optimization of the foaming structure by precisely controlling the synergistic effect of melt viscosity and foaming dynamics. The high temperature of the surface layer (180-220°C) promotes the rapid melting and flow of bio-based polypropylene, forming a dense surface layer under the nucleation effect of nano-silica. At the same time, the high shear rate inhibits the diffusion of the foaming agent to the surface layer, avoiding surface pore defects; the low temperature of the middle layer (160-210°C) maintains the high elastic modulus of the melt, slows the diffusion rate of supercritical CO2, controls the bubble nucleation and growth process, and forms a uniform closed-cell structure; the medium temperature of the bottom layer (170-210°C) balances the dispersion of bamboo fiber and melt fluidity, and avoids the destruction of the pore structure by fiber agglomeration through moderate shear. This three-dimensional synergistic mechanism of temperature, viscosity, and foaming breaks through the bottleneck of premature decomposition of the foaming agent or insufficient melt strength in the traditional single-temperature extrusion process.

[0094] The experimental results of Comparative Example 4 (uniform extrusion temperature of 175°C) verified the necessity of temperature stratification: the melt viscosity in the high-temperature zone (such as the surface layer) was too low, resulting in the formation of large-sized merged holes when the CO2 was rapidly depressurized at the die outlet; the melt viscosity in the low-temperature zone (such as the middle layer) was too high, and the foaming agent could not fully diffuse, forming partially unfoamed dense blocks. This heterogeneity of the foaming structure directly led to the expansion of the material density fluctuation range to 0.38-0.72g / cm 3 , significantly weakening the lightweight advantage. At the same time, the increase in open porosity (>40%) increases the water absorption rate of the material, affecting its stability in a humid environment.

[0095] The layered temperature control strategy of the present invention deeply combines the rheological properties in polymer processing with the foaming dynamics, and realizes the simultaneous optimization of foaming pore size, closed-cell ratio and interlayer interface through the temperature field design in the spatial dimension. Compared with the traditional process, this technology improves the pore size uniformity of the foaming layer by more than 2 times (standard deviation <25μm vs. >50μm), and the closed-cell ratio is stabilized at more than 90%, providing a solution with both structural strength and functionality for the application of lightweight materials in the fields of automotive interiors, building insulation, etc. This innovation expands the "structure-performance" customization capability of polymer materials from single component regulation to multi-dimensional coordination of process parameters, promoting the upgrading of green manufacturing technology.

[0096] Test Example 4: Supercritical CO2 vs. physical blowing agent foaming effect comparison test description Experimental procedure Sample preparation Example 3: Low carbon TPO material prepared with minimum component allocation ratio, using supercritical CO2 blowing agent Comparative Example 5: Same components as Example 3, but replace supercritical CO2 with equal amount of azodicarbonamide (physical blowing agent).

[0097] Foaming process Example 3: In supercritical CO2 foaming device, set foaming temperature 160°C, pressure 12 MPa, pressure holding time 15 minutes; Comparative Example 5: Premix azodicarbonamide (2 parts) with matrix, and foam in flat vulcanizing machine at 170°C, 8 MPa for 20 minutes.

[0098] Closed cell rate test Use gas adsorption analyzer (nitrogen adsorption method) to measure the closed cell rate of the foamed layer, take 3 parallel samples for each group.

[0099] Compression resilience rate test Cut the foamed layer into 20x20x10mm 3 Test sample, use universal testing machine to compress to 50% deformation at a rate of 50mm / min; after unloading, stand for 10 minutes, measure the thickness recovery rate (ASTM D3574).

[0100] Cell structure analysis Break the test sample in liquid nitrogen, observe the cell morphology (magnification 500x) by scanning electron microscope (SEM) after gold spraying treatment.

[0101] The experimental results are shown in Table 4: Table 4 - Supercritical CO2 vs. physical blowing agent performance comparison test data Group Closed cell rate (%) Compression resilience rate (%) SEM typical morphology description Example 3 96.2 88.5 Uniform pore size, complete pore wall Comparative Example 5 68.4 57.2 Pore wall is broken, open cell rate > 40% From the experimental results in Table 4, we can get: Supercritical CO2 foaming technology realizes efficient nucleation and uniform growth of nanoscale cells through the physical mechanism of swelling-decompression. In the supercritical state, CO2 forms a homogeneous mixed system with the polymer matrix, and the gas solubility sharply decreases during the decompression process, which triggers homogeneous nucleation. Combined with the viscoelasticity regulation of the dynamic crosslinking network, the bubble size is limited in the micron range (80-120μm), the cell wall thickness is uniform and complete. While physical blowing agents (such as azodicarbonamide) rely on thermal decomposition to generate gas, the dynamic matching of decomposition temperature and melt viscosity is poor, resulting in local enrichment of gas to form large size merged cells (>200μm), and decomposition residues (such as ammonia, urea compounds) form defect points in the matrix, further weakening the cell wall strength.

[0102] The test data of Comparative Example 5 shows that the gas released in the decomposition process of the physical foaming agent cannot be effectively bound by the dynamic crosslinking network, and the bubble merging and rupture leads to a decrease in the closed cell rate to below 70%, and the compression resilience rate is less than 62%. In addition, the acid-base reaction between the decomposition products of azodicarbonamide and the hydroxyl groups on the surface of bamboo fibers exacerbates the fiber-matrix interface debonding, forming a vicious cycle of bubble structure defects and mechanical property deterioration. In contrast, the inert nature of supercritical CO2 avoids the occurrence of side reactions, and its rapid diffusion capacity ensures that the foaming process does not leave impurities, allowing the material to be lightweight while maintaining high closed cell rate (>92%) and resilience stability.

[0103] Test Example 5: Test Description of the Effect of Heat Press Crosslinking on High Temperature Dimensional Stability Experimental Steps Sample Preparation Example 3: Low-carbon TPO material was prepared according to the minimum component allocation ratio, and heat press crosslinking was performed at 160℃ / 0.8MPa for 20 minutes; Comparative Example 6: The same components as Example 3, but omitting the heat press crosslinking step.

[0104] High Temperature Dimensional Stability Test Cut the sample into 50x50x5mm 3 Thin slices, vertically placed in an 80℃ oven for 24 hours; Use a digital micrometer to measure the thickness change rate (initial thickness T0, thickness after treatment T1, formula: ΔT = (T1-T0) / T0x100%); Test 5 samples per group, take the maximum and minimum values as the fluctuation range.

[0105] Dynamic Mechanical Analysis (DMA) Use a dynamic mechanical analyzer, test temperature range 30-120℃, heating rate 3℃ / min, frequency 1Hz; Record the storage modulus (E’) at 80℃, take 3 parallel samples per group.

[0106] Microscopic Morphology Observation After high temperature treatment, the sample is brittle fractured in liquid nitrogen, and the surface and fracture morphology is observed by SEM, focusing on the thermal deformation area.

[0107] The experimental results are shown in Table 5: Table 5 - Test Data of the Effect of Heat Press Crosslinking on High Temperature Dimensional Stability Group Thickness change rate (%) 80°C storage modulus (MPa) SEM morphology description Example 3 1.5 523 Smooth surface, no warping or cracking Comparative Example 6 10.5 178 Local melting and collapse of matrix From the experimental results in Table 5, we can conclude that: The hot-pressing crosslinking process endows the material with excellent high-temperature dimensional stability through three-dimensional reconstruction of dynamic covalent bond networks. At 160℃ / 0.8MPa, the furan-maleimide (F-MI) dynamic crosslinker undergoes reversible Diels-Alder reaction with the active groups at the end of polypropylene molecular chains, forming a crosslinking network throughout the matrix and the interface with bamboo fibers. This network continuously dissipates thermal stress at high temperatures (80℃) through the breakage-recombination mechanism of dynamic bonds, inhibiting irreversible slippage of molecular chains and fiber-matrix interface peeling, so that the thickness change rate of the material is controlled within 2.5%. In contrast, the uncrosslinked material lacks a dynamic network constraint, and the difference in thermal expansion coefficient between the bamboo fibers (≈8×10 -6 / ℃) and the matrix (≈1.2×10 -4 / ℃) induces interfacial shear stress, resulting in a thickness expansion of more than 10% and a storage modulus drop of more than 70%.

[0108] Dynamic mechanical analysis (DMA) data further reveal the strengthening effect of the crosslinking network on high-temperature rigidity: Example 3 still maintains a storage modulus of 487-523 MPa at 80℃, indicating that the dynamic crosslinking network effectively limits the movement of molecular chain segments, while the reversible dissociation of crosslinking points avoids the brittle fracture risk of traditional chemical crosslinking. This combination of rigidity and flexibility enables the material to resist deformation in high-temperature environments and repair local micro-damage through dynamic bond recombination, significantly distinguishing it from the creep failure (storage modulus <200 MPa) and pore structure collapse of the uncrosslinked material in Comparative Example 6.

[0109] The hot-pressing crosslinking technology of the present application deeply couples dynamic covalent chemistry with processing technology, breaking through the application bottleneck of traditional polyolefin materials prone to deformation at high temperatures. By precisely controlling the crosslinking density and network topology through process parameters (temperature / pressure), the material maintains dimensional stability (ΔT <3%) in a wide temperature range of -30℃ to 120℃, while avoiding the difficulty of regenerative processing caused by over-crosslinking. This innovation provides a solution with high reliability and easy recyclability for application scenarios such as automotive interior parts and building insulation boards that need to withstand long-term thermal cycles, promoting the leap from laboratory performance to engineering of low-carbon materials.

[0110] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A low carbon TPO material and a method for preparing the same, characterized in that, The low-carbon TPO material comprises the following components by mass fraction: Bio-based polypropylene: 45-55 parts; Recycled TPO particles: 25-35 parts; Bamboo fibers: 15-25 parts; Dynamic covalent crosslinking agent: 0.5-2.0 parts; Supercritical fluid foaming agent: 2-4 parts; Nano-silica: 2-5 parts.

2. The low carbon TPO material of claim 1, wherein, The low-carbon TPO material is composed of a three-layer composite structure, which comprises: Surface layer: a dense layer composed of bio-based polypropylene and nano-silica; Middle layer: a foamed layer containing a dynamic crosslinking network; Bottom layer: a bamboo fiber reinforced layer.

3. The low carbon TPO material of claim 2, wherein, The thickness of the three-layer composite structure is respectively: Surface layer: 0.1-0.2 mm; Middle layer: 0.2-0.5 mm; Bottom layer: 0.2-0.5 mm.

4. The low carbon TPO material of claim 1, wherein, The bamboo fibers are double-modified bamboo fibers with surface grafting of silane coupling agent and maleic anhydride, with a grafting rate of 85-95%.

5. A low carbon TPO material and a method for preparing the same according to claim 1, wherein, The supercritical fluid foaming agent is supercritical CO2.

6. A process for the preparation of a low carbon TPO material as claimed in any one of claims 1 to 5, characterized in that, The method comprises the following steps: S1, pretreating bio-based polypropylene, recycled TPO particles, and bamboo fibers to obtain compatible raw materials; S2, melt blending the pretreated raw materials with a dynamic covalent crosslinking agent and a supercritical fluid foaming agent to form a dynamic crosslinking TPO matrix; S3, processing the dynamic crosslinking TPO matrix into a three-layer composite structure blank through a multi-layer co-extrusion foaming process; S4, hot pressing and crosslinking the blank to activate the dynamic covalent bond network; S5, surface functionalization treatment of the crosslinked material to obtain the low-carbon TPO material.

7. The method for preparing a low-carbon TPO material according to claim 6, characterized in that: The step S1 comprises: Bio-based polypropylene is vacuum dried at 80-85°C for 3-4 hours; Recycled TPO particles are blended and granulated with maleic anhydride grafted polypropylene at a mass ratio of 95:5; Bamboo fibers are double-grafted and modified with silane coupling agent KH550 and maleic anhydride.

8. The method for preparing a low-carbon TPO material according to claim 6, characterized in that: The temperature control for layering co-extrusion in step S3 is: Surface layer extrusion temperature: 180-220°C; Middle layer extrusion temperature: 160-210°C; Bottom layer extrusion temperature: 170-210°C.

9. The method of claim 6, wherein the low carbon TPO material is prepared by, The conditions for hot pressing and dynamic crosslinking in step S4 are: Temperature: 120-130°C; Pressure: 7-10 MPa; Pressure holding time: 4-6 minutes.

10. The method for preparing a low-carbon TPO material according to claim 6, characterized in that: The surface functionalization treatment in step S5 comprises: Coating with water-based acrylic-silicone hybrid paint, forming a wear-resistant coating after curing; Forming a leather-like texture on the surface through embossing process.

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