Regenerated plastic composite sheet and preparation method thereof

Abstract

The invention provides a reprocessed plastic composite sheet and a preparation method thereof, the composite sheet comprises 80-95% of recycled plastic particles, 0.5-5% of a nano aluminum silicate molecular sieve, 0.5-2% of a microsphere encapsulated free radical scavenger and 0.5-2% of a processing aid, a dynamic crosslinking prepolymer forms a self-repairing network during processing based on a Diels-Alder reversible reaction mechanism, and the self-repairing network is used for repairing the reprocessed plastic particles. The viscosity of a melt is reduced through high-temperature decrosslinking, the strength is improved through recombination after cooling, the fatigue resistance of the regenerated plastic is remarkably improved, NIPAM-co-AAc temperature-sensitive microspheres are shrunk through hot pressing triggering, hindered amine / phenol antioxidants are accurately released, and thermal oxidation degradation is inhibited. The preparation process adopts multi-stage mixing and hot-pressing stabilization to realize uniform dispersion of the nano molecular sieve, interface compatibility of fluoride and dynamic cross-linked network recombination, finally obtains the regenerated plastic sheet with a flat surface, breaks through the performance limitation of regenerated plastic, can be widely applied to the fields of packaging, construction and automobiles, and has environmental protection property and economical efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of plastic composite sheets, in particular to a recycled composite sheet prepared using recycled plastic as raw material, and also relates to a preparation method of the recycled plastic composite sheet. Background Art

[0002] As the consumption of soft plastic products continues to increase, so too does the amount of discarded soft plastic products. To reduce resource waste, improve plastic recycling rates, and mitigate pollution, governments around the world are supporting flexible packaging suppliers through taxation or subsidies to develop sustainable, recyclable packaging materials and recycling methods, such as biodegradable / recycled plastics and the reuse of discarded products. Currently, the former, as shown in invention patent publication number CN103059384A, uses masterbatch blending with recycled plastic to produce recycled plastic, but this method cannot be used for multiple recycling of recycled plastic. The latter, however, relies on economic efficiency to become the primary method for preparing recycled plastic composite sheets.

[0003] However, traditional recycled plastics suffer from issues such as residual sulfur / nitrogen compounds and cleaning agents from secondary processing, which can make residual odors difficult to eliminate. Free radical crosslinking during secondary processing can also lead to molecular chain breakage and crosslinked foreign matter, limiting their application in recycled products. Furthermore, free radical crosslinking can also form large molecular particles (fisheyes) in recycled plastic composite sheets, which can easily lead to uneven printed surfaces.

[0004] Therefore, there is an urgent need for a new type of recycled plastic composite sheet to solve the above technical problems. Summary of the Invention

[0005] The purpose of the present invention is to provide a plastic composite sheet to solve the problems of performance degradation, quality reduction and secondary processing of existing recycled plastics during multiple recycling, while overcoming the problem of uneven surface of products produced by existing recycled plastic composite sheets.

[0006] To achieve the above objectives, the present invention provides the following technical solutions: In a first aspect, the present invention provides a recycled plastic composite sheet, comprising, by weight percentage: 80-95% recycled plastic particles, 0.5-5% nano-aluminum silicate molecular sieve, 0.5-2% free radical scavenger, and 0.5-2% processing aid; The particle size of the recycled plastic particles is 50-200 μm; the processing aid includes 0.1-1% of the total mass of the composite sheet as a fluoride additive and 0.1-0.3% of a furan / maleimide dynamic cross-linked prepolymer; and the free radical scavenger is encapsulated with NIPAM-co-AAc microspheres.

[0007] Recycled plastic pellets refer to granular, recycled materials made by crushing, cleaning, melting, and granulating discarded plastics, such as bottles, packaging bags, and industrial waste. These are typically melted at high temperatures and then extruded into uniform particles using a mold. While effective during experiments, the present invention still favors using primary recycled plastics for granulation. For secondary and higher recycled plastics, the performance degradation using the present invention's recycling method is slightly higher than that of primary recycled plastics, at 9-13%. As a preferred embodiment, the recycled plastic pellets are made of a material selected from polyolefins, polyesters, and more particularly, at least one of polyethylene, polypropylene, polyvinyl chloride, and polyester.

[0008] Furan / maleimide dynamically crosslinked prepolymers are prepolymers that reversibly form crosslinks during the polymer formation process. Dynamic crosslinking typically refers to the ability of crosslinks to break and reform under specific conditions, such as temperature fluctuations. Furan / maleimide dynamically crosslinked prepolymers contain Diels-Alder units.

[0009] Nano-aluminosilicate molecular sieves are a type of inorganic material with a regular nanoscale pore structure. They have a silicon and aluminum oxide skeleton and carry a cationic charge balance. In the present invention, unless otherwise specified, faujasite-type molecular sieve materials are used. As a preferred embodiment, the nano-aluminosilicate molecular sieve has a specific surface area > 500 m 2 / g. Improvements such as grafting amino groups, sulfonic acid groups, and other functional groups to enhance adsorption, and even acid / base etching to selectively dissolve part of the framework aluminum and expand the pore size, as well as other types of molecular sieve materials, are generally advisable, provided they can achieve equivalent functions and do not violate the technical concepts and principles of the present invention.

[0010] Free radical scavengers are chemical substances or biomolecules capable of neutralizing free radicals. They are often used to terminate free radical chain reactions and protect the target system from free radical damage. Optional agents include, but are not limited to, vitamin C, vitamin E, tea polyphenols, resveratrol, carotenoids, thiols, butylated hydroxyanisole, and the like. Preferred embodiments include hindered amines, phenolic antioxidants, and thioesters.

[0011] Fluoride additives refer to functional additives with fluoride or fluorine-containing compounds as their core components, including but not limited to sodium fluoride, calcium fluoride, aluminum fluoride, hexafluorophosphate, fluorosilicates, and cryolite. In the present invention, fluoride additives form a low-surface-energy interface layer during processing, effectively reducing the interfacial tension between the plastic substrate and the nano-aluminosilicate molecular sieve. In a preferred embodiment, the fluoride additive is selected from calcium fluoride and / or magnesium fluoride.

[0012] As a preferred embodiment, the NIPAM-co-AAc microspheres have a particle size of 1-10 μm, and the molar ratio of AAc (acrylic acid) monomer in the microsphere shell is 15-25%. The crosslinker is N, N'-methylenebisacrylamide. NIPAM refers to N-isopropylacrylamide. The NIPAM-co-AAc microspheres have a high specific surface area, which facilitates efficient loading of the free radical scavenger.

[0013] In a second aspect, the present invention further provides a method for preparing a recycled plastic composite sheet having at least one of the above technical features, the steps comprising: S1, sorting and cleaning the recycled plastic particles, and performing metal ion activation treatment on the nano-aluminum silicate molecular sieve; S2, preparation of furan / maleimide dynamic cross-linked prepolymer and NIPAM-co-AAc microsphere encapsulated free radical scavenger; S3, using a multi-stage mixing process to mix the recycled plastic particles, nano-aluminum silicate molecular sieve, free radical scavenger and processing aid, and then extruding and granulating; S4, performing a hot pressing stabilization treatment on the raw materials and activating the response function of the NIPAM-co-AAc microspheres.

[0014] As a preferred embodiment, in said S1, the sorting includes at least one of gravity sorting, infrared sorting, and electrostatic sorting; In S2, furan and maleimide are reacted in a molar ratio of 1:1 under a protective atmosphere at 60°C ± 2°C for 4 hours to prepare a prepolymer solution with a solid content of 40±5%; In S3, the mixing and granulation is carried out in three stages: the first stage is to add the recycled plastic particles and the aluminum silicate molecular sieve at 75-85°C and 500-700 rpm for mixing; the second stage is to mix at 95-105°C and 700-900 rpm for 2 minutes; the third stage is to mix at 115-125°C and 1100-1300 rpm for 5 minutes; In the above-mentioned S4, the hot pressing stabilization treatment includes hot pressing at 155-165° C. and 0.8 MPa pressure for 10 minutes, followed by gradual cooling.

[0015] As a preferred embodiment, the preparation method of the NIPAM-co-AAc microspheres comprises dissolving NIPAM (N-isopropylacrylamide) and AAc (acrylic acid) in a mixed solvent, precooling under nitrogen protection, adding N,N'-methylenebisacrylamide to initiate polymerization, and freeze-drying to obtain porous microspheres.

[0016] As a preferred embodiment, the method for loading the NIPAM-co-AAc microspheres with the free radical scavenger comprises immersing the microspheres in a solution containing the free radical scavenger and then drying the solution.

[0017] The advantages and beneficial effects of the present invention are: 1. This invention utilizes nano-aluminosilicate molecular sieves to absorb impurities in recycled plastics, reducing performance degradation while also enhancing interfacial bonding between molecular chains and suppressing stress cracking during secondary processing. The furan / maleimide dynamically crosslinked prepolymer forms a reversible network structure during processing. This dynamically decrosslinks under high-temperature shear forces to reduce melt viscosity, and then recrosslinks upon cooling to restore strength. This imparts excellent fatigue resistance and processing fluidity to the sheet, addressing the problem of reduced toughness after repeated recycling of conventional recycled plastics.

[0018] 2. NIPAM-co-AAc microspheres achieve on-demand release of free radical scavengers through a temperature-responsive shell. During high-temperature processing, the microspheres shrink and release antioxidants, precisely inhibiting thermal oxidative degradation. At room temperature, the microspheres seal and protect the active ingredients, extending their service life.

[0019] 3. The present invention also provides a processing method for recycled plastic composite sheets, which optimizes the dispersibility of each component by staged heating and variable speed mixing, and disperses the nanomolecular sieve at low temperature and medium speed to avoid agglomeration; activates the dynamic cross-linking prepolymer at medium temperature and high speed; and achieves full compatibility between the fluoride additive and the plastic matrix at high temperature and ultra-high speed.

[0020] 4. The roller temperature gradually increases and then decreases, combined with a linear speed gradient, to achieve a melt stretching-setting balance. This effectively eliminates internal stress in the sheet, reducing warping and surface ripples. Hot pressing combined with a gradient cooling process activates the dynamic cross-linking network reorganization, while promoting the contraction of the microsphere shell and the release of antioxidants, forming a stable sheet microstructure and resulting in a smooth finished surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a process flow chart for preparing the recycled plastic composite sheet of the present invention. DETAILED DESCRIPTION

[0022] The present invention provides a recycled plastic composite sheet comprising recycled plastic particles, nano-aluminosilicate molecular sieves, a free radical scavenger, and a processing aid. The recycled plastic particles have a particle size of 50-200 μm. The processing aid comprises a fluoride additive (0.1-1% by weight of the composite sheet) and a furan / maleimide dynamically cross-linked prepolymer (0.1-0.3% by weight of the composite sheet). The free radical scavenger is encapsulated with NIPAM-co-AAc microspheres.

[0023] Nano-aluminosilicate molecular sieves use their porous structure to absorb and capture residual sulfur and nitrogen compounds and small molecule impurities in recycled plastics. Their silicon-aluminum ratio (SiO2 / Al2O3, 5:1 in this invention unless otherwise specified) determines their cation exchange capacity, immobilizing negatively charged contaminants through ionic bonding. During sol-gel or hydrothermal synthesis, the hydrolysis of the silicon and aluminum sources in nano-aluminosilicate molecular sieves generates hydroxyl-containing intermediates (such as Si-OH and Al-OH). If the polycondensation reaction is incomplete, some hydroxyl groups remain on the surface of the skeleton. These surface hydroxyl groups form hydrogen bonds with the plastic molecular chains, reducing damage to the chains by impurities and inhibiting stress cracking during secondary processing.

[0024] As an explanation, the source of hydroxyl groups on the surface of nano-aluminosilicate molecular sieves can be the dissociation of water molecules by the Lewis acid sites of aluminum oxide tetrahedron after adsorption; the molecular sieve framework may be partially broken during synthesis or post-treatment to form unsaturated Si + or Al 3+ Dangling bonds react with water molecules; acid washing or cation exchange, etc. Furthermore, when the nano-aluminosilicate molecular sieve is calcined at high temperature to remove the template, some hydroxyl groups are removed, but after cooling, water molecules are re-adsorbed to form hydroxyl groups. For this embodiment, rehydration at a specific temperature can control the hydroxyl density.

[0025] The molecular sieve surface forms a physical anchor with the plastic matrix through silicon-oxygen bonds, enhancing the interfacial bonding strength between the molecular chains. Simultaneously, fluoride additives (such as CaF2 / MgF2) form a low-surface-energy interfacial layer during the mixing process, reducing melt flow resistance and promoting uniform dispersion of the nanomolecular sieve. The furan / maleimide dynamically crosslinked prepolymer, based on the Diels-Alder reaction (DA reaction), forms a thermoreversible crosslinked network at low temperatures (<90°C) and undergoes a reverse reaction to decouple the crosslinks at high temperatures (>120°C).

[0026] As an explanation, the Diels-Alder reaction (DA reaction) is a [4+2] cycloaddition reaction between a diene and a dienophile under heating or specific conditions to form a six-membered ring structure.

[0027] Furan / maleimide dynamically cross-linked prepolymers decrosslink during the processing of recycled plastic pellets. This is partly due to lowering melt viscosity, improving fluidity, and reducing fisheye defects. Another reason is that the cross-linked network is restructured during the cooling phase, restoring material strength and imparting fatigue resistance and multi-recycling stability to the sheet. Notably, microcracks generated in recycled plastics using these cross-linked prepolymers during service can be triggered by localized heating to trigger a reverse DA reaction, releasing molecular chain mobility. Subsequent cooling restructures the cross-linked network, achieving self-healing of the cracks.

[0028] Free radical scavengers are commonly used in plastic processing to inhibit the free radical chain reaction caused by thermal oxidative degradation. The defects of directly adding antioxidants in traditional processes include that the antioxidants start to decompose during the mixing stage and cannot effectively protect the subsequent high-temperature forming process; the unembedded antioxidants are prone to migrate to the surface and volatilize or exude. The above defects result in a loss rate of 30-50% for the antioxidants directly added during the plastic recycling process each time of recycling and granulation, directly or indirectly leading to a decline in antioxidant efficiency after 3 cycles of plastic recycling. At the same time, uneven oxidation sites will cause fluctuations in the melt flow index (MFI) of up to 25%, and in addition, it also makes the recycled plastic yellow, affecting the product appearance.

[0029] The way for this invention to overcome the above problems is to use NIPAM-co-AAc microspheres to coat the free radical scavenger, and the acrylic monomer provides hydrophilic groups to combine with the molecules of the free radical scavenger. At the processing temperature, the microsphere shell layer shrinks and ruptures, releasing the hindered amine / phenolic antioxidant to inhibit the free radicals of thermal oxidative degradation; at room temperature, the microspheres are closed to protect the activity of the antioxidant. The high loading of the antioxidant is achieved through the porous structure and hydrophilic groups of the microspheres. During the hot pressing process, the temperature gradient drives the antioxidant to diffuse into the plastic matrix to form a uniform protective layer.

[0030] The release process of the free radical scavenger dissociated from the microspheres conforms to the coupling mechanism of Fickian diffusion and shell layer shrinkage, and can be described by the improved Peppas equation: In the formula: M t / M ∞ is the proportion of the release amount at time t (g / g), k1 is the rate constant of the diffusion process (min -n , n is the release exponent, and its value in the system of this invention is 0.18±0.03), k2 is the release coefficient dominated by shrinkage (dimensionless, and its value in the system of this invention is 0.82±0.05), β is the rate constant of shell layer shrinkage (min -1 , and its value in the system of this invention is 0.2±0.02). t is the release time (min).

[0031] When the release exponent n≤0.43, that is, when the microspheres are intact, the free radical release rate is controlled by Fickian diffusion; when 0.43 < n < 0.85, the diffusion-swelling mechanism proceeds synergistically; when n≥0.85, that is, after the microspheres rupture, the release of the free radical scavenger is dominated by erosion.

[0032] , where In the formula, δ is the shell layer thickness (nm, and it is 300nm in the system of this invention); η is the polymer viscosity (Pa·s, and it is approximately 10 at 155°C 4Pa·s). In the present invention, Ea can be estimated to be 45.3 kJ / mol, β0=2.1×10 6 min -1 .

[0033] When k2 / k1 > 5, the microsphere's free radical scavenger is dominated by shrinkage, and the temperature at this point can be considered the critical rupture temperature. This patent achieved 8.7 at 155°C. When βt > 3, the microspheres are considered completely released. This patent achieved βt = 2.5 after 10 minutes of hot pressing, indicating a residual free radical scavenger rate of less than 5%.

[0034] The present invention also provides a method for preparing the aforementioned recycled plastic sheet, which utilizes a multi-stage mixing process. In the first stage, low-temperature, medium-speed mixing prevents nano-molecular sieve agglomeration. This temperature range softens the surface of the plastic particles but does not yet melt them. During this time, the nano-molecular sieve preferentially adsorbs to the surface of the plastic particles through hydrogen bonding, forming a pre-dispersed "core-shell" structure. A fluoride additive initially wets the surface of the plastic particles.

[0035] In the second stage, the dynamically crosslinked prepolymer is activated at medium temperature and high speed. The plastic matrix reaches the melting point. Medium-high shear forces cause the furan / maleimide prepolymer to disassociate into monomers, reducing the apparent viscosity of the melt. This initiates the DA reaction to form primary crosslinking points with a diameter of 200-500nm.

[0036] In the third stage, high-temperature, ultra-high-speed shearing creates a localized temperature gradient, exfoliating and dispersing the nano-molecular sieve while simultaneously creating full compatibility between the molten plastic matrix and the additive. Simultaneously, high-speed shearing orients the molecular chains along the flow direction. The fluoride additive forms a transition layer at the plastic / molecular sieve interface, aligning the molecular sieve along the shear field, creating enhanced anisotropy and improving the longitudinal strength of the sheet.

[0037] The molten melt is formed into a sheet through four continuous rollers with gradient settings for temperature and line speed. Roller I provides initial melt plasticization and eliminates agglomerates; Roller II enhances melt fluidity and initiates dynamic crosslinking; Roller III provides high-temperature, high-shear refinement and molecular chain stretching; Roller IV rapidly cools and sets the shape, locking in the crosslinked network. The high-temperature section of Roller III reduces internal stress by stretching the melt, while the cooling section of Roller IV (below the DA reaction temperature) promotes crosslinking network reorganization. Simultaneously, the high line speed inhibits excessive crystal growth and reduces surface waviness.

[0038] The formed sheet is stabilized by hot pressing to restructure its microstructure. Hot pressing partially dissociates DA crosslinks, rearranges the molecular segments, and eliminates residual stress from processing. Subsequently, gradient cooling gradually restores the crosslink density, forming a uniform network structure. The pressure of hot pressing drives the microspheres to a rupture rate exceeding 90%, releasing antioxidants. Simultaneously, fluoride migrates to the plastic / molecular sieve interface under pressure, forming a CaF2 and / or MgF2 composite layer, reducing interfacial energy and improving impact resistance.

[0039] The sheet can be recycled at least five times, with a tensile strength retention rate of >80%, breaking through the bottleneck of traditional recycled plastics that experience a sharp drop in performance after three cycles.

[0040] The following embodiments are further described in conjunction with the accompanying drawings and examples. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0041] Example 1 A recycled plastic composite sheet, the composition of which is as follows by weight: specific surface area 600m 2 / g nano aluminum silicate molecular sieve 3%, 5μm microsphere encapsulated hindered amine radical scavenger 1.5%, calcium fluoride 0.5%, furan / maleimide dynamic cross-linking prepolymer 0.2%, and the balance are recycled polyethylene particles with a particle size of 150±30μm.

[0042] Its preparation method is: S1: Electrostatic separation is used to remove metal impurities, and 60℃ alkaline washing is used to recover polyethylene particles.

[0043] S2: Furan and maleimide were mixed in a 1:1 molar ratio and reacted at 62°C for 4 h under nitrogen to obtain a dynamically cross-linked prepolymer; the molar proportion of AAc in the NIPAM-co-AAc microspheres was 20%, and the amount of the cross-linker MBA was 2% of the total monomer mass.

[0044] S3: multi-stage mixing, first stage: 80 °C, 600 rpm mixing for 10 min; Second stage: 100°C, 800 rpm mixing for 2 min; The third stage: mixing at 120°C and 1200 rpm for 5 minutes.

[0045] S4: hot pressing the composite-molded recycled plastic composite sheet at 160° C. and 0.8 MPa for 10 min, and then gradually cooling it to room temperature.

[0046] Example 2 A recycled plastic composite sheet, which differs from Example 1 in that its composition is: specific surface area 550m 2 / g nano aluminum silicate molecular sieve 4%, microspheres encapsulating phenolic radical scavenger with a particle size of 3 μm 2%, magnesium fluoride 0.8%, furan / maleimide dynamic cross-linking prepolymer 0.3%, and the balance are recycled polypropylene particles with a particle size of 100±20 μm.

[0047] In its preparation method: In S3, the temperature of the third stage is increased to 125°C to enhance the interfacial compatibility of magnesium fluoride.

[0048] In S4, hot pressing was started at 165 °C to activate more microspheres to release antioxidants.

[0049] Example 3 A recycled plastic composite sheet, which differs from Example 1 in that its composition is: specific surface area 700m 2 / g nano-aluminum silicate molecular sieve 2%, microspheres encapsulating thioester free radical scavenger with a particle size of 10μm 1%, magnesium fluoride / magnesium fluoride (1:1) 0.6%, furan / maleimide dynamic cross-linked prepolymer 0.15%, and the balance are recycled polyethylene terephthalate particles with a particle size of 200±20μm.

[0050] In its preparation method: In S4, a two-step gradient cooling was used to lock the molecular orientation. Specifically, the sheet was transferred to an oven and cooled from 160°C to 120°C at 5°C / min, and then cooled from 120°C to 80°C at 2°C / min. Finally, the oven was closed and cooled to room temperature.

[0051] Example 4 A recycled plastic composite sheet, which differs from Example 1 in that its composition is: specific surface area 800m 2 / g nano aluminum silicate molecular sieve 5%, 8 μm microsphere encapsulated hindered amine + phenol free radical scavenger 1.8%, magnesium fluoride 1%, furan / maleimide dynamic cross-linking prepolymer 0.25%, and the balance is recycled polyethylene terephthalate particles with a particle size of 50±5 μm.

[0052] In its preparation method: In S1, infrared sorting is added to remove foreign plastics.

[0053] In S2, the molar proportion of microspheres AAc reached 25% to enhance PVC compatibility.

[0054] Example 5 A recycled plastic composite sheet, which differs from Example 1 in that its components are: 4% nano-aluminosilicate molecular sieve with a specific surface area of ​​680 m2 / g, 1.2% of a hindered amine free radical scavenger encapsulated in microspheres with a particle size of 6 μm, 0.8% of sodium fluoride, 0.3% of a furan / maleimide dynamic cross-linking prepolymer, and the balance being recycled polypropylene particles with a particle size of 180±20 μm.

[0055] In its preparation method: In S3: The third stage was mixed at 1300 rpm for 6 min to compensate for the higher surface energy of sodium fluoride.

[0056] In S4, the hot pressing temperature is lowered to 150°C.

[0057] Example 6 A recycled plastic composite sheet comprises the following components by weight: 0.5% of a nano-aluminosilicate molecular sieve with a specific surface area of ​​500 m2 / g, 1.5% of a microsphere-encapsulated phenolic free radical scavenger with a particle size of 10 μm, 0.5% of magnesium fluoride, 0.2% of a furan / maleimide dynamic cross-linking prepolymer, and the balance of recycled polyester particles with a particle size of 70 μm.

[0058] Its preparation method is: S1: After removing metal impurities by electrostatic separation, the recovered polyester was treated with 10% HCl for 2 h and then alkaline washed at 60 °C.

[0059] Comparative Example 1 The difference from Example 1 is that no fluoride additive is added, and the gaps in the relevant materials are replaced with recycled polyethylene particles.

[0060] Comparative Example 2 The difference from Example 1 is that no nano molecular sieve is added, and the gaps in the relevant materials are replaced with recycled polyethylene particles.

[0061] Comparative Example 3 The difference from Example 1 is that the antioxidant is a directly added hindered amine substance without microsphere encapsulation.

[0062] Comparative Example 4 The difference from Example 1 is that no dynamically cross-linked prepolymer is added, and polyester particles are used to replace the material gaps.

[0063] The following performance tests were performed on each of the above examples and comparative examples. The tensile strength retention rate was measured according to ISO 527-1: the specimen was formed into a dumbbell shape, stretched at a speed of 50 mm / min, and the strength after 5 cycles was compared to the original strength. The heat deformation temperature was measured according to ISO 75-1: the temperature at which the specimen was subjected to a load of 1.8 MPa, a heating rate of 2°C / min, and a bending deformation of 0.25 mm. The surface roughness Ra was measured according to ISO 4287 using a contact profilometer with a sampling length of 0.8 mm and an evaluation length of 5 mm. The flatness deviation was measured according to ASTM D5947: the laser thickness gauge was used to measure the extreme difference at 10 points in the transverse direction of the sheet. The yellowing index ΔYI was measured according to ASTM E313 using a colorimeter, an aging chamber at 85°C / 85% RH, and a D65 light source for 100 hours. The number of recyclable cycles refers to the strength of each cycle tested according to ISO 527 being greater than or equal to 80% of the original specimen. As can be seen from the above table, the present invention significantly improves the comprehensive performance of recycled plastic composite sheets through the four core technologies of dynamic cross-linking network reorganization, thermosensitive microsphere encapsulated antioxidants, nano-molecular sieve adsorption enhancement, and fluoride interface compatibility, breaking through the three major bottlenecks of traditional recycled plastics, namely, multiple recycling performance decline, serious surface defects, and low antioxidant efficiency. Examples 1-6 still meet the use requirements after 4 cycles. Comparative Examples 1-4 lack fluoride, molecular sieve, microsphere encapsulated antioxidant and dynamic cross-linked body, respectively, and their regeneration performance drops sharply, which fully demonstrates that the present invention has achieved a comprehensive improvement in the dimensions of mechanical properties, heat resistance, surface quality, cycle life, etc. of recycled plastic composite sheets through the technical innovation of dynamic network self-repair, precise controlled release of antioxidants, nano-enhancement and interface optimization.

[0064] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A recycled plastic composite sheet, characterized in that: The composite sheet comprises the following components by weight percentage: 80-95% recycled plastic particles with a particle size of 50-200 μm; 0.5-5% nano-aluminum silicate molecular sieve; 0.5-2% free radical scavenger, which is encapsulated with NIPAM-co-AAc microspheres; and 0.5-2% processing aid, which includes 0.1-1% of the total mass of the composite sheet as a fluoride additive and 0.1-0.3% of a furan / maleimide dynamic cross-linking prepolymer.

2. The recycled plastic composite sheet according to claim 1, characterized in that: The material of the recycled plastic particles is selected from at least one of polyethylene, polypropylene, polyvinyl chloride and polyester.

3. The recycled plastic composite sheet according to claim 1, characterized in that: The specific surface area of ​​the nano-aluminosilicate molecular sieve is greater than 500 m 2 / g.

4. The recycled plastic composite sheet according to claim 3, characterized in that: The free radical scavenger is selected from at least one of hindered amines, phenolic antioxidants, and thioesters.

5. The recycled plastic composite sheet according to claim 3, characterized in that: The fluoride adjuvant is selected from calcium fluoride and / or magnesium fluoride.

6. The recycled plastic composite sheet according to claim 1, characterized in that: The particle size of the NIPAM-co-AAc microspheres is 1-10 μm, wherein the molar proportion of acrylic acid monomer is 15-25%, and the cross-linking agent is N,N'-methylenebisacrylamide.

7. The method for preparing a recycled plastic composite sheet according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1, sorting, cleaning and recycling plastic particles and activating nano-aluminum silicate molecular sieves; S2, preparation of furan / maleimide dynamic cross-linked prepolymer and NIPAM-co-AAc microsphere encapsulated free radical scavenger; S3, mixing raw materials and extruding granulation; S4, hot pressing the raw materials of the particles into sheets to activate the function of the microspheres.

8. The preparation method according to claim 7, characterized in that: The S1 sorting includes at least one of gravity sorting, infrared sorting, and electrostatic sorting; The furan and maleimide in S2 are reacted in a molar ratio of 1:1 at 60±2° C. under a protective atmosphere for 4 hours to obtain a prepolymer solution with a solid content of 40±5%; The S3 mixing granulation includes three stages: the first stage is to mix the recycled plastic particles and the molecular sieve at 75-85°C and 500-700 rpm; the second stage is to mix at 95-105°C and 700-900 rpm for 2 minutes; the third stage is to mix at 115-125°C and 1100-1300 rpm for 5 minutes; The S4 heat treatment conditions are 155-165° C., 0.8 MPa, hot pressing for 10 minutes, and then gradient cooling.

9. The preparation method according to claim 7, characterized in that: The preparation method of the NIPAM-co-AAc microspheres comprises dissolving NIPAM and AAc in a mixed solvent, precooling under a protective atmosphere, adding an initiator, and freeze-drying to obtain porous microspheres.

10. The preparation method according to claim 9, characterized in that: The method for loading the NIPAM-co-AAc microspheres with the free radical scavenger comprises immersing the microspheres in a solution containing the free radical scavenger and then drying the solution.

Images