Preparation method of waste plastic fiber reinforced wood-plastic composite material

Abstract

The invention relates to the technical field of polymer composite materials, and discloses a preparation method of a waste plastic fiber reinforced wood-plastic composite material. According to the invention, 30-70% by weight of waste polyolefin, 10-50% by weight of wood flour, 5-30% by weight of waste PET fiber, 1-10% by weight of an epoxy functionalized elastomer and 0.05-1% by weight of a dynamic rearrangement catalyst are blended. Extruding at a specific thermodynamic window of 185-210 DEG C, and carrying out ring-opening addition on a high-concentration end group generated by degradation of the waste PET and an elastomer, so as to construct a confined dynamic covalent bond network at a multi-phase interface. The network is dynamically exchanged at the temperature higher than the topological freezing transition temperature, and good melt flowability is maintained; after cooling, rigid-flexible-rigid chemical anchoring is formed, and matrix crystallization is not interfered. The performance of conventional physical blending is improved, and the prepared composite material has good creep resistance and notch impact toughness and can be applied to the fields of high-bearing outdoor building materials, automobile anti-collision accessories and the like.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a method for preparing wood-plastic composite materials reinforced with waste plastic fibers. Background Technology

[0002] Wood-plastic composites (WPCs), as a core carrier of the polymer circular economy, have achieved large-scale application. In recent years, to further improve the mechanical limits of WPCs, the introduction of waste high-rigidity / high-melting-point plastic fibers (such as waste PET textile fibers) has become a cutting-edge research topic in this field. However, extensive industrial practice and microscopic thermodynamic research have shown that, in existing blending systems, there is extremely strong interfacial repulsion between polar wood flour, non-polar polyolefin resins, and high-rigidity PET fibers, leading to the following long-standing performance limitations in this field:

[0003] (1) Mutual exclusion of rigidity and toughness: Although the introduction of high-modulus waste PET fibers can improve the static tensile strength of the material, when subjected to impact, due to the lack of energy dissipation channels of chemical bonding, micro-slippage and stress concentration are likely to occur at the interface. Macroscopically, this is manifested as: while the rigidity of the material is improved, the elongation at break and the notched impact toughness decrease significantly, exhibiting brittle fracture characteristics.

[0004] (2) Rheological challenges of high solids content filler and processing resistance: Increasing the solid volume fraction of wood flour and waste fiber will lead to a significant increase in the apparent melt viscosity of the composite system, resulting in greater hydrodynamic resistance, which may cause overload of extrusion equipment or carbonization of materials.

[0005] (3) Adverse effects of conventional compatibilizers on matrix crystallinity: Existing technologies typically introduce block copolymers or anhydride-grafted elastomers as compatibilizers. Amorphous flexible elastomer segments will undergo thermodynamic diffusion into the interior of the polyolefin matrix, interfering with the crystallization kinetics of the semi-crystalline plastic matrix, leading to a decrease in the overall crystallinity of the material, and consequently a reduction in creep resistance and elastic modulus.

[0006] Therefore, developing a method for preparing wood-plastic composites reinforced with waste plastic fibers has become an urgent technical problem to be solved in the field of polymer composites. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing wood-plastic composite materials reinforced with waste plastic fibers. This invention seeks to solve the system embrittlement problem caused by the introduction of rigid fibers into existing wood-plastic composite materials, overcome the melt rheological processing barriers under high solids content filling, and avoid the damage to the crystallinity of the polyolefin matrix caused by conventional compatibilizers, thereby preparing a high-load-bearing composite material that combines high tensile strength, excellent notched impact toughness, and long-term creep resistance.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing wood-plastic composite material reinforced with waste plastic fibers, comprising the following steps:

[0009] S1. Weigh the following components by weight percentage: 30.0%-70.0% waste polyolefin resin; 10.0%-50.0% wood flour; 5.0%-30.0% waste PET fiber; 1.0%-5.0% epoxy functionalized elastomer; 0.05%-1.0% dynamic rearrangement catalyst;

[0010] S2. The above components are mixed and then fed into a twin-screw extruder for melt blending and extrusion; the epoxy functionalized elastomer is glycidyl methacrylate grafted polyolefin elastomer (POE-g-GMA); the dynamic rearrangement catalyst is selected from one or more combinations of zinc acetylacetonate, cobalt acetylacetonate, or 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD);

[0011] The extrusion processing temperature T of the twin-screw extruder is set to 185°C-210°C, and is guaranteed to be higher than the topological freezing transition temperature Tv of the composite system. The melt residence time of the composite system in the extruder is controlled between 60s and 180s.

[0012] Further, the weight percentage of the raw material components is preferably: 45.0%-55.0% waste polyolefin resin, 25.0%-35.0% wood flour, 10.0%-15.0% waste PET fiber, 3.0%-5.0% epoxy functionalized elastomer, and 0.1%-0.3% dynamic rearrangement catalyst.

[0013] Further, the epoxy-functionalized elastomer is glycidyl methacrylate grafted polyolefin elastomer (POE-g-GMA); the dynamic rearrangement catalyst is selected from one or more combinations of zinc acetylacetonate, cobalt acetylacetonate, or 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD).

[0014] Furthermore, during the melt blending process of S2, the epoxy groups of the epoxy-functionalized elastomer undergo ring-opening reactions with the hydroxyl groups on the surface of the wood flour and the end groups of the waste PET fibers, respectively, to form... -Hydroxy ether bond and -Hydroxy ester bonds; a cross-linked network is constructed at the multiphase interface of the wood flour, waste PET fiber and waste polyolefin resin; and at temperature Under a shear field, the dynamic rearrangement catalyst promotes dynamic topological exchange between the ester and ether bonds, reducing the apparent melt viscosity η of the composite system in the extruder to between 1250 Pa·s and 1450 Pa·s.

[0015] Furthermore, the waste PET fibers have an average length of 2.0mm-6.0mm and an aspect ratio of 15-40 before extrusion; the wood flour has a particle size of 80-120 mesh and a moisture content of [missing information - likely related to moisture content before extrusion]. .

[0016] Furthermore, the intrinsic viscosity IV of the waste PET fiber is 0.45 dL / g-0.65 dL / g, and the end carboxyl group content is ≥40 meq / kg.

[0017] Furthermore, the waste polyolefin resin is a mixture of waste polyethylene (PE) and waste polypropylene (PP), and the weight ratio of waste polyethylene (PE) to waste polypropylene (PP) is 1:3 to 3:1.

[0018] Furthermore, the twin-screw extruder in S2 has an aspect ratio (L / D) of 32-56, an extrusion processing temperature (T) of 185℃-210℃, and a screw speed of 100rpm-400rpm; the twin-screw extruder is equipped with a shearing and kneading block in the screw assembly, and the melt residence time of the composite system in the extruder is controlled between 60s and 180s.

[0019] Furthermore, S1 also includes auxiliary additives accounting for 0.5%-2.0% of the total weight, wherein the auxiliary additives are selected from one or more of antioxidants, ultraviolet absorbers, pigments or flame retardants.

[0020] Furthermore, the twin-screw extruder described in S2 is provided with at least one natural venting zone and two vacuum venting zones along the material extrusion direction; the absolute pressure of the vacuum venting zone is controlled between -0.08MPa and -0.095MPa.

[0021] Furthermore, when applied to high load-bearing outdoor building materials, the raw material components include, by weight percentage: 45.0% waste polypropylene resin, 25.0% wood flour, 15.0% waste PET fiber with an aspect ratio of 30, 3.0% glycidyl methacrylate grafted polyolefin elastomer (POE-g-GMA), and 0.2% 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD).

[0022] Furthermore, when applied to high-impact automotive parts, the raw material components include, by weight percentage: 50.0% of a mixture of waste PE and PP (the weight ratio of waste polyethylene (PE) to waste polypropylene (PP) is 1:3 to 3:1), 35.0% of wood flour with a particle size of 120 mesh, 9.7% of waste PET fiber, 5.0% of glycidyl methacrylate grafted polyolefin elastomer (POE-g-GMA), and 0.3% of cobalt acetylacetone.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects:

[0024] (1) Actual test data show that while maintaining a tensile strength of 46.5 MPa, the notched impact strength of the present invention is increased to 26.5 kJ / m², which is significantly improved compared with conventional physical blending or traditional compatibility systems.

[0025] (2) Traditional chemical crosslinking leads to a significant increase in the apparent viscosity of the composite system, causing the extrusion equipment to overload and shut down. This invention introduces a specific proportion of dynamic rearrangement catalyst, which releases flow resistance through bond breaking and recombination of macromolecular chain segments, reducing the apparent viscosity of the melt to about 1250 Pa·s. Even with a PET fiber content of 15%, it still exhibits good thermoplastic processing performance.

[0026] (3) The dynamic covalent bonds of the present invention bind the flexible elastomer at the three-phase interface, and this physical constraint restricts its ability to be released into the polyolefin matrix. The continuous phase matrix maintains a high crystallinity of up to 48.5%. The creep strain rate of the material of the present invention is 0.48% after 1000 hours of testing at 50°C and a constant stress of 20 MPa, demonstrating good long-term creep resistance.

[0027] (4) The waste raw materials of the present invention construct a denser interfacial cross-linking network, which not only reduces the cost of raw materials, but also achieves a significant cross-linking density gain in microscopic chemical mechanism. Attached Figure Description

[0028] Figure 1 This is a flowchart of the preparation process of the present invention;

[0029] Figure 2 This is a schematic diagram of the microscopic mechanism of the present invention;

[0030] Figure 3 This is a line graph comparing the mechanical properties (rigidity and toughness) of the present invention;

[0031] Figure 4 It is a line graph comparing rheological processing properties (apparent viscosity of melt). Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] This invention provides a method for preparing wood-plastic composite materials reinforced with waste plastic fibers. This invention aims to solve technical problems in conventional wood-plastic composite materials, such as decreased toughness due to the addition of rigid fibers, increased melt viscosity due to increased solid content, and reduced matrix crystallinity due to the addition of compatibilizers.

[0034] Its mechanism of action mainly includes: utilizing a specific ratio of epoxy-functionalized elastomers and dynamic catalysts to construct an interfacial-confined dynamic covalent bond network at the multiphase interface of polar wood flour, waste PET fibers, and non-polar polyolefins. The specific microscopic mechanism is as follows:

[0035] 1. Constructing energy dissipation and stress transfer structures: The epoxy groups of epoxy-functionalized elastomers (such as POE-g-GMA) and the hydroxyl groups on the surface of wood flour ( The terminal carboxyl or hydroxyl groups of waste PET fibers undergo ring-opening reactions to generate... -Hydroxy ether bond and -Hydroxy ester bonds. Under stress, the flexible segments of the elastomer act as a buffer layer to absorb energy, while the covalent bond network effectively transfers stress to the PET fibers, thereby improving the tensile strength and impact toughness of the material.

[0036] 2. Crossing Topological dynamic exchange: The introduction of dynamic rearrangement catalysts endows cross-linked networks with glassy polymer-like properties.

[0037] In this invention, the topological freezing transition temperature Tv refers to the temperature at which the characteristic relaxation time of the system reaches the critical value for solid-state transition. It can be determined by temperature scanning using a dynamic thermomechanical analyzer (DMA) or a rotational rheometer, measuring the intersection of the storage modulus and loss modulus of the system, or by fitting the stress relaxation time using the Arrhenius formula.

[0038] In the extrusion stage ( Covalent networks undergo topological rearrangement, maintaining a low apparent melt viscosity. After cooling ( Dynamic reactions are restricted, and solidification forms a stable cross-linked network.

[0039] 3. Thermodynamic confinement effect at the interface: The cross-linked network is mainly distributed at the three-phase interface, forming spatial constraints that limit the diffusion of flexible elastomer segments into the polyolefin matrix. This maintains a high degree of crystallinity with minimal impact on the ordered arrangement of polymer segments in the matrix. And creep resistance.

[0040] 4. Reaction Equilibrium and Resistance to Hydrolysis Lock-in: In the extrusion process, this invention employs a multi-stage vacuum degassing process (-0.08MPa to -0.095MPa) to remove residual moisture from the wood flour. This reduces high-temperature foaming defects. Simultaneously, during the topological rearrangement stage, the system continuously removes vaporized moisture and small molecule byproducts released from the transesterification reaction, reducing the risk of high-temperature hydrolysis and deactivation of the dynamic rearrangement catalyst by moisture, and promoting the forward cross-linking reaction between the end groups of waste PET and the epoxy groups of the elastomer.

[0041] In addition, waste PET fibers expose more end carboxyl groups (CEG) than virgin PET due to thermomechanical degradation. The degradation end groups (POE-g-GMA) and terminal hydroxyl groups can undergo ring-opening addition reactions with the epoxy groups in POE-g-GMA under the action of a dynamic rearrangement catalyst. This invention utilizes waste PET fibers, which can construct a covalent network with high crosslinking density at the interface, achieving high-value reuse of waste resources.

[0042] Example 1

[0043] Set extrusion processing temperature The temperature range of 185℃–210℃ is a comprehensive selection based on the thermodynamic and kinetic properties of the multiphase system.

[0044] (1) This temperature range allows the waste PP / PE matrix to fully melt and the catalyst to be at a temperature higher than that of the PP / PE matrix. Dynamic topology switching is triggered under certain conditions;

[0045] (2) Avoid the drastic thermal degradation temperature of hemicellulose in wood flour (>220℃) to reduce product pores and foaming defects caused by volatile gases;

[0046] (3) Utilizing the high melting point of PET (>250℃), the waste PET fiber maintains an unmelted rigid skeleton shape within this temperature range; combined with the shear field generated by the screw speed of 100–400 rpm and the material residence time of 60–180 s, dynamic covalent bonds undergo an interfacial reaction between the unmelted PET fiber surface and the molten polyolefin / wood powder.

[0047] The system of this invention exhibits good compatibility with both metal Lewis acid catalysts (such as zinc acetylacetonate and cobalt acetylacetonate) and strong organic base catalysts (such as 1,5,7-triazabicyclo[4.4.0]dec-5-ene, TBD). Thermodynamic tests show that, within the addition range of 0.05wt%–1.0wt%, both types of catalysts can reduce the apparent activation energy of the interfacial covalent network. Lowering it to the 50–70 kJ / mol range reduces the topological freezing transition temperature. It stabilizes at approximately 160°C, thus adapting to an extrusion processing window of 185°C–210°C.

[0048] To demonstrate the technical effectiveness of the present invention and verify its applicability, the following basic embodiments and comparative test matrices (Table 1) and comparative embodiments for specific application scenarios (Table 2) were designed.

[0049] Table 1: Summary of Comprehensive Performance Test Data of Basic Embodiments and Comparative Examples of the Invention

[0050]

[0051] As shown in Table 1, compared with Comparative Example 3 which used a conventional compatibilizer, Example 1 showed a significant improvement in both tensile strength and impact toughness, and the matrix crystallinity was also improved. The melt apparent viscosity remained stable; compared to Comparative Example 2, the melt apparent viscosity decreased after the introduction of a dynamic catalyst. The pressure was reduced from 3850 Pa·s to 1250 Pa·s, improving the problem of continuous extrusion processing difficulties in traditional chemical crosslinking systems. Furthermore, Comparative Example 4 demonstrates that when the elastomer content increases to 8 wt%, the crystallinity... The significant decrease in tensile strength indicates that the numerical range defined by this invention has a critical significance for the technical effect.

[0052] To further demonstrate the applicability of this invention in the fields of high load-bearing outdoor building materials and high impact-resistant automotive parts, and to verify the rationality of the formulation boundaries of this application, the applicant conducted the following supplementary experiments. The test results are shown in Table 2:

[0053]

[0054] In the tests in Table 2, for Example 3 and Comparative Example 3-A, which are for high-impact automotive parts, the room temperature cantilever beam notched impact strength and flexural modulus were mainly examined. Therefore, the 1000-hour creep strain rate test was not performed on them (indicated by '-' in the table).

[0055] Example 2: Application in high-load-bearing outdoor building material scenarios

[0056] Formulation composition (by weight): 45wt% waste PP resin, 25wt% wood flour (80 mesh), 15wt% waste PET fiber (length-to-diameter ratio 30), 3wt% POE-g-GMA, 0.2wt% TBD, 1.8wt% antioxidant / UV absorber composite package.

[0057] Performance: Under conditions of extrusion at 200℃ and PET fiber content of 15wt%, the system still maintains good melt flowability. After cooling and molding, the cross-linked network effectively bonds the PET fibers to the PP matrix. Tests showed that the sample had a flexural modulus of 5200 MPa; under continuous loading at 50°C and a constant stress of 20 MPa for 1000 hours, its creep strain rate was 0.48%. In contrast, Comparative Example 2-A, with the same formulation but without TBD, lacked interfacial dynamic covalent bonding, resulting in interfacial micro-slippage under high loads and a creep strain rate of 2.15%. This comparison confirms the substantial technical effectiveness of this invention in terms of creep resistance.

[0058] Example 3: Application in high-impact automotive parts scenarios

[0059] Formula composition (by mass percentage): 50wt% waste PE / PP mixture (where the mass ratio of PE to PP is 1:1), 35wt% wood flour (120 mesh), 9.7wt% waste PET textile filaments, 5wt% POE-g-GMA, 0.3wt% cobalt acetylacetone.

[0060] Performance: This embodiment uses 120-mesh wood flour with a larger specific surface area. Under cobalt acetylacetonate catalysis, POE segments form a chemical anchoring layer on the surface of the wood flour and PET fibers. Matrix crystallinity. The percentage was 46.2%. Macroscopic testing showed that while maintaining a tensile strength of 35 MPa, the material achieved a notched cantilever beam impact strength of 26.5 kJ / m² at room temperature. Furthermore, Comparative Example 3-A (containing 6 wt% POE-g-GMA) indicated that when the elastomer content exceeded 5 wt%, some POE segments interfered with matrix crystallization, leading to… The modulus decreased to 35.8%, and the flexural modulus dropped to 2100 MPa. This result further corroborates the necessity and rationality of the numerical range setting in this application.

[0061] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0062] 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 the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing wood-plastic composite material reinforced with waste plastic fibers, characterized in that, Includes the following steps: S1. Weigh the following raw material components by weight percentage: waste polyolefin resin 30.0%-70.0%; wood flour 10.0%-50.0%; waste PET fiber 5.0%-30.0%; epoxy functionalized elastomer 1.0%-5.0%; dynamic rearrangement catalyst 0.05%-1.0%; S2. The above components are mixed and then fed into a twin-screw extruder for melt blending and extrusion; the epoxy functionalized elastomer is glycidyl methacrylate grafted polyolefin elastomer (POE-g-GMA); the dynamic rearrangement catalyst is selected from one or more combinations of zinc acetylacetonate, cobalt acetylacetonate, or 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD); The extrusion processing temperature T of the twin-screw extruder is set to 185°C-210°C, and is guaranteed to be higher than the topological freezing transition temperature Tv of the composite system. The melt residence time of the composite system in the extruder is controlled between 60s and 180s.

2. The preparation method according to claim 1, characterized in that, The preferred weight percentages of the raw material components are: 45.0%-55.0% waste polyolefin resin, 25.0%-35.0% wood flour, 10.0%-15.0% waste PET fiber, 3.0%-5.0% epoxy functionalized elastomer, and 0.1%-0.3% dynamic rearrangement catalyst.

3. The preparation method according to claim 1, characterized in that, During the melt blending process of S2, the epoxy groups of the epoxy-functionalized elastomer undergo ring-opening reactions with the hydroxyl groups on the surface of wood flour and the end groups of waste PET fibers, respectively, to form... -Hydroxy ether bond and -Hydroxy ester bonds; a cross-linked network is constructed at the multiphase interface of the wood flour, waste PET fiber and waste polyolefin resin; and at temperature Under a shear field, the dynamic rearrangement catalyst promotes dynamic topological exchange between the ester and ether bonds, reducing the apparent melt viscosity η of the composite system in the extruder to between 1250 Pa·s and 1450 Pa·s.

4. The preparation method according to claim 1, characterized in that, The waste PET fibers have an average length of 2.0mm-6.0mm and an aspect ratio of 15-40 before extrusion; the wood flour has a particle size of 80-120 mesh and a moisture content of [missing information - likely related to moisture content before extrusion]. .

5. The preparation method according to claim 1, characterized in that, The intrinsic viscosity (IV) of the waste PET fiber is 0.45 dL / g-0.65 dL / g, and the end carboxyl group content is ≥40 meq / kg.

6. The preparation method according to claim 1, characterized in that, The waste polyolefin resin is a mixture of waste polyethylene (PE) and waste polypropylene (PP), and the weight ratio of waste polyethylene (PE) to waste polypropylene (PP) is 1:3 to 3:

1.

7. The preparation method according to claim 1, characterized in that, The twin-screw extruder in S2 has a length-to-diameter ratio (L / D) of 32-56 and a screw speed of 100rpm-400rpm; the screw assembly of the twin-screw extruder is equipped with a shearing and kneading block; The twin-screw extruder described in S2 is provided with at least one natural venting zone and two vacuum venting zones along the material extrusion direction; the absolute pressure of the vacuum venting zone is controlled between -0.08MPa and -0.095MPa.

8. The preparation method according to claim 1, characterized in that, S1 also includes auxiliary additives accounting for 0.5%-2.0% of the total weight, wherein the auxiliary additives are selected from one or more of antioxidants, ultraviolet absorbers, pigments or flame retardants.

9. The preparation method according to claim 1, characterized in that, When applied to high load-bearing outdoor building materials, the raw material components include, by weight percentage: 45.0% waste polypropylene resin, 25.0% wood flour, 15.0% waste PET fiber with an aspect ratio of 30, 3.0% glycidyl methacrylate grafted polyolefin elastomer (POE-g-GMA), and 0.2% 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD).

10. The preparation method according to claim 1, characterized in that, When applied to high-impact automotive parts, the raw material components include, by weight percentage: 50.0% of a mixture of waste polyethylene (PE) and waste polypropylene (PP) (the weight ratio of waste polyethylene (PE) to waste polypropylene (PP) is 1:3 to 3:1), 35.0% of wood flour with a particle size of 120 mesh, 9.7% of waste PET fiber, 5.0% of glycidyl methacrylate grafted polyolefin elastomer (POE-g-GMA), and 0.3% of cobalt acetylacetone.

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