Synergistic repair and stable modification method for high-performance recycled polypropylene and composite material thereof

Abstract

The invention discloses a synergistic repair and stabilization modification method for high-performance recycled polypropylene (rPP) and a composite material thereof. According to the method, rPP, a specific amount of chain repairing agent, a specific amount of synergistic stabilization composite additive, a specific amount of odor adsorption / screening agent, a specific amount of nucleating agent and the like are subjected to melt blending in a double-screw extruder. The core of the invention lies in that the chain repair agent is utilized to chemically repair the broken molecular chain of the rPP and neutralize acidic substances, the synergistic stabilizer is utilized to decompose peroxide and capture free radicals to form a'repair-stability 'dual protection mechanism, and physical adsorption and devolatilization are combined to more comprehensively solve the problems of poor performance, low stability, strong odor and the like of the rPP. The obtained modified rPP has higher strength than conventional blending modified recycled polypropylene, excellent thermal stability and low odor grade, can be widely applied to the high-value fields of automobiles, household appliances and the like, and realizes high value-added recycling of rPP.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polymer material recycling and reusing, and particularly relates to a modification method for recycling polypropylene (rPP) by chemical repair, stabilization modification and odor masking, so as to significantly improve the mechanical properties, thermal stability and odor grade of the rPP, and make the rPP applicable to high-performance fields such as automobile parts and household appliance shells. BACKGROUND

[0002] Polypropylene (PP) has become one of the most widely used plastics in the world due to its excellent comprehensive performance, low cost and wide application. However, a large amount of PP waste is generated, and how to realize its high-value recycling and utilization is of great significance for resource conservation and environmental protection.

[0003] However, during the processing, use and aging process of PP, the molecular chain will be broken due to the action of heat, oxygen, ultraviolet light and other factors, resulting in a decrease in molecular weight and an increase in melt index. At the same time, oxidation reactions also occur, generating oxygen-containing aging residues such as hydroperoxides, ketones, aldehydes and carboxylic acids. These degradation products result in the following inherent defects of recycled polypropylene (rPP):

[0004] 1. Significant decrease in mechanical properties: the key indicators such as impact strength and tensile strength are much lower than those of new materials, and cannot meet the requirements of high-performance automobile parts. 2. Poor thermal and oxidative stability: the residual hydroperoxides and carboxylic acids in the material can catalyze further degradation during subsequent processing and use, forming a "self-catalytic" effect and shortening the service life. 3. Bad odor: small molecules of aldehydes, ketones and carboxylic acids are the main sources of VOC and irritating odor, which seriously limits their application in relatively closed environments such as automobile interiors. 4. Yellowing of color: the oxidation products of phenolic antioxidants, such as quinones, cause the rPP to turn yellow and gray, resulting in poor appearance quality.

[0005] At present, the conventional modification methods for rPP mainly include simple addition of new materials or elastomers for "dilution" and toughening, and supplement of antioxidants. However, these methods have obvious limitations: 1. Simple blending: cannot fundamentally solve the problems of molecular chain breakage and aging residues, and the performance improvement is limited, and the odor and color problems are still prominent. 2. Supplement of antioxidants: can only delay subsequent aging to a certain extent, but has little effect on the degradation that has already occurred and the existing acidic substances. 3. Physical devolatilization: can remove part of the small molecule volatile substances, but has limited effect on the polar groups and acidic substances bonded on the molecular chain.

[0006] Therefore, developing a comprehensive technical solution that can actively "repair" the damaged molecular chain, effectively "neutralize" the aging residues, and comprehensively "stabilize" the material performance is the key to realizing the high-performance value-added modification of rPP, and is also the technical breakthrough urgently needed by the current industry. SUMMARY

[0007] The present application aims to overcome the limitations of the prior art and provide a synergistic repair and stabilization modification method for high-performance recycled polypropylene. This method, through the synergistic effect of the three levels of "repair-stabilization-sensory improvement", not only effectively restores the mechanical properties of rPP, but also fundamentally improves its thermal stability, odor and color, so that the modified rPP material can be widely used in the fields of automotive interior and exterior, household appliances and other demanding materials.

[0008] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0009] A synergistic repair and stabilization modification method for high-performance recycled polypropylene, comprising the following steps:

[0010] 1. Raw material preparation: by weight, it contains the following components: recycled polypropylene (rPP) resin: 70-90 parts; chain repair agent: 0.3-2.0 parts; synergistic stabilization composite additive: 0.5-1.5 parts; odor adsorption / covering agent: 0.5-2.0 parts; nucleating agent: 0.2-0.5 parts; processing aid: 0.1-0.5 parts; optionally, toughening agent: 5-15 parts; optionally, reinforcing filler: 10-20 parts.

[0011] 2. Pre-mixing treatment: place all the above components in a high-speed mixer and mix at room temperature for 3-8 minutes to ensure uniform dispersion of each additive in the rPP matrix.

[0012] 3. Melt blending and repair reaction: the pre-mixed material is sent into a twin-screw extruder for melt blending, reaction extrusion and granulation. The preferred extrusion process parameters are: zone 1 temperature 170-180℃, zone 2 temperature 180-200℃, zone 3 to zone 7 temperature 200-220℃, die temperature 205-225℃; screw speed 300-500rpm; vacuum devolatilization port maintains a vacuum degree of-0.08 to-0.10MPa.

[0013] The core of the technical solution of the present application lies in the unique design of the chain repair agent and the synergistic stabilization composite additive and their synergistic mechanism:

[0014] 1. Chain repair agent: a multi-functional epoxy polymer with epoxy value controlled at 0.05-0.15 mol / 100g. Its mechanism of action is that the multiple epoxy groups distributed on its molecular chain can chemically react with the functional groups such as carboxyl and hydroxyl at the end of rPP molecular chain to form stable covalent bonds. This process realizes two functions-chain extension and acid neutralization. Chain extension: reconnects multiple broken rPP short chains, effectively increases the weight average molecular weight of the material, thereby restoring its melt strength and mechanical properties, especially impact strength and tensile strength. Acid neutralization: reacts with carboxylic acid to form stable ester bonds, eliminating the catalytic effect of carboxylic acid on the further degradation of PP, and fundamentally improving the thermal stability of the material.

[0015] 2. Synergistic stabilization complexing agent: compounded by primary antioxidant, auxiliary antioxidant and acid absorbent in a specific ratio (preferably 1:(0.8-1.5):(0.5-1.2)). The primary antioxidant is a hindered phenolic antioxidant, such as antioxidant 1010, which is used to capture free radicals generated during the degradation process and terminate chain reactions. The auxiliary antioxidant is a phosphite antioxidant, such as antioxidant 168. Its core role is to decompose the existing hydroperoxide in rPP at high processing temperature, reducing it to stable alcohol, preventing it from decomposing into new free radicals. This is a perfect complement to the role of chain repair agent: the repair agent treats carboxylic acid, and the auxiliary antioxidant treats hydroperoxide. The acid absorbent is a compound of calcium stearate and synthetic hydrotalcite, which provides additional acid-base buffering for the system, captures any residual or newly generated acidic substances, and produces a synergistic effect with the auxiliary antioxidant to protect it from being poisoned by acidic substances.

[0016] The three-stage synergistic mechanism is as follows:

[0017] 1. First-order repair (chemical repair): the chain repair agent actively repairs broken molecular chains and neutralizes acidic centers through chemical reactions.

[0018] 2. Secondary stabilization (synergistic stabilization): the synergistic stabilization complexing agent decomposes residual peroxide, captures free radicals, and provides acid-base buffering to create a long-term stable internal environment.

[0019] 3. Third-stage improvement (sensory improvement): odor adsorption / masking agents and nucleating agents further improve the sensory quality and processing performance of the material from the aspects of physical adsorption and improved microstructure, respectively. Vacuum devolatilization process is more effective in removing small molecular volatile substances under the synergistic effect.

[0020] The beneficial effects of the present application are:

[0021] Compared with the prior art, the present application has the following significant advantages:

[0022] 1. Excellent performance recovery: through the "molecular suture" effect of the chain repair agent, the impact strength of the modified rPP of the application can be recovered to 85%~95% of the new material level, the tensile strength is recovered to more than 90%, and the melt index stability is greatly improved.

[0023] 2. Long-term thermal stability: the unique synergistic stabilizing system eliminates the "seeds" (hydroperoxide and carboxylic acid) that initiate degradation, so that the performance retention rate of the modified rPP after multiple extrusion processes is much higher than that of the conventional system with simple addition of antioxidants.

[0024] 3. Low odor: combined with chemical neutralization, physical adsorption and vacuum devolatilization, the odor grade of rPP can be effectively improved.

[0025] 4. High added value and wide application: the comprehensive performance of the rPP modified by the scheme can meet the technical requirements of automobile door panels, bottom guard plates, battery pack non-structural parts, household appliance shells and the like, realizing the leap from "downgrade use" to "same level or even upgrade use", and having great economic value and environmental protection value.

[0026] 5. Good process compatibility: the method described in the application can be directly realized on a general twin-screw extruder without special equipment, and is convenient for large-scale industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a schematic diagram of the core action mechanism of the modification method of the application.

[0028] Figure 2 is a comparison curve of the melt flow rate change (thermal stability) of examples 1-3 and comparative examples 1-2 after three extrusions. DETAILED DESCRIPTION

[0029] The application will be further described in detail below in combination with specific examples. The following examples are only used to illustrate the application, and should not be regarded as limiting the scope of the application.

[0030] Example 1: Modified rPP suitable for automobile interior base material

[0031] Formulation: recycled PP (broken material, melt index about 25 g / 10 min): 80 parts, toughening agent POE: 10 parts, chain repair agent (multi-functional epoxy polymer, epoxy value 0.08): 0.8 parts, synergistic stabilizing composite additive (antioxidant 1010:168: calcium stearate / hydrotalcite = 1:1.2:0.8): 1.0 part, odor adsorbent (zeolite molecular sieve): 1.5 parts, nucleating agent (sorbitol): 0.3 parts, processing aid (calcium stearate): 0.2 parts

[0032] Preparation process: after weighing each component according to the above proportion, pour them into a high-speed mixer, mix at low speed for 2 minutes, and mix at high speed for 3 minutes. Put the mixed material into a co-rotating parallel twin-screw extruder (length-diameter ratio 40:1) for melt blending. Temperature setting: zone 1 175℃, zone 2 190℃, zone 3-7 210℃, die head 215℃. Screw speed 400 rpm, vacuum degree -0.09 MPa. The extruded strip is cooled by water, dried by air, cut into particles, and modified rPP particles are obtained.

[0033] Example 2: Reinforced flame-retardant modified rPP suitable for electric tool housing

[0034] Formula: Recycled PP: 70 parts, halogen-free flame retardant (ammonium polyphosphate / melamine cyanurate compound system): 15 parts, chain repair agent (epoxy value 0.12): 1.2 parts, synergistic stabilizing composite auxiliary (antioxidant 1010:168:hydrotalcite = 1:1:1): 1.2 parts, odor masking agent (vanillin master batch): 1.0 part, nucleating agent: 0.3, processing aid: 0.3 parts

[0035] Preparation process: same as Example 1.

[0036] Example 3: High-rigidity modified rPP suitable for automobile underbody panel

[0037] Formula: Recycled PP: 60 parts, new material PP (homopolymer): 20 parts, talc (1250 mesh): 20 parts, chain repair agent (epoxy value 0.05): 0.5 parts, synergistic stabilizing composite auxiliary (antioxidant 1010:168:calcium stearate = 1:1.5:1): 0.8 parts, nucleating agent: 0.4 parts, processing aid: 0.3 parts

[0038] Preparation process: same as Example 1.

[0039] Comparative Example 1

[0040] Simple blending method is used: 85 parts of recycled PP + 15 parts of polyolefin elastomer (POE) + 0.5 parts of antioxidant 1010. Preparation process is the same as Example 1.

[0041] Comparative Example 2

[0042] Conventional stabilization method is used: 80 parts of recycled PP + 10 parts of POE + 0.5 parts of antioxidant 1010 + 0.5 parts of antioxidant 168 + 0.5 parts of calcium stearate. Preparation process is the same as Example 1.

[0043] Performance testing and result analysis

[0044] The particles obtained in the above examples and comparative examples are dried at 80℃ for 4 hours, and then injection molded into standard test bars for performance testing. The test results are shown in the following table:

[0045]

[0046]

[0047] Result analysis: 1. Mechanical properties: Examples 1-3 are significantly superior to the two comparative examples in impact and tensile strength, especially Examples 1 and 3, which indicates that the repair-stabilizing system of the present application effectively repairs the molecular weight of rPP and stabilizes its structure. 2. Thermal stability: Taking the "melting index change rate after three extrusions" as the evaluation index, the change rate of Examples 1-3 is much lower than that of the comparative examples, which fully proves that the synergistic system gives the material excellent resistance to multiple processing. Odor: The odor grade of the examples is improved, while Comparative Examples 1 and 2 still have poor sensory quality because the fundamental problem has not been solved.

[0048] The above description is only the preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above with the preferred embodiment, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the present application, and any simple modification, equivalent change and modification made to the above examples according to the technical essence of the present application still belong to the scope of the technical solution of the present application.

Claims

1. A method for the synergistic remediation and stabilization modification of high-performance recycled polypropylene, characterized in that, Includes the following steps: a) Raw material preparation: by weight, including 70-90 parts of recycled polypropylene, 0.3-2.0 parts of chain repair agent, 0.5-1.5 parts of synergistic stabilizing composite additive, 0.5-2.0 parts of odor adsorbent / masking agent, 0.2-0.5 parts of nucleating agent and 0.1-0.5 parts of processing aid; b) Premixing: Place all components from step a) in a mixer and mix them evenly; c) Melt blending and repair reaction: The premixed material is fed into a twin-screw extruder and melt blended, reacted, extruded and granulated at a temperature range of 170 to 230°C and a vacuum of -0.08 to -0.10 MPa. The chain repair agent is a multifunctional epoxy polymer with an epoxy value of 0.05-0.15 mol / 100g; the synergistic stabilizing composite additive is composed of a primary antioxidant, an auxiliary antioxidant, and an acid absorbent in a mass ratio of 1:(0.8-1.5):(0.5-1.2).

2. The method for synergistic remediation and stabilization modification of high-performance recycled polypropylene according to claim 1, characterized in that, The chain repair agent is selected from one of epoxy-functionalized acrylate copolymers, epoxy-functionalized styrene-acrylate copolymers, or epoxy-modified polyolefins.

3. The method for synergistic remediation and stabilization modification of high-performance recycled polypropylene according to claim 1, characterized in that, The primary antioxidant is a hindered phenolic antioxidant; the secondary antioxidant is a phosphite or phosphonate antioxidant; and the acid absorber is a compound of one or two of calcium stearate, zinc stearate, and synthetic hydrotalcite.

4. The method for synergistic remediation and stabilization modification of high-performance recycled polypropylene according to claim 1, characterized in that, The odor adsorbent / masking agent is one of zeolite molecular sieve, activated carbon, diatomaceous earth, or vanillin-based odor masking masterbatch.

5. The method for synergistic remediation and stabilization modification of high-performance recycled polypropylene according to claim 1, characterized in that, The formulation also includes 5 to 15 parts of a toughening agent, which is one of POE, EPDM, and SEBS.

6. The method for synergistic remediation and stabilization modification of high-performance recycled polypropylene according to claim 1, characterized in that, The formulation also includes 10 to 20 parts of reinforcing filler, which is one of talc, calcium carbonate, glass fiber, glass microspheres, etc.

7. The method for synergistic remediation and stabilization modification of high-performance recycled polypropylene according to claim 1, characterized in that, The screw speed of the twin-screw extruder is 300-500 rpm.

8. A high-performance recycled polypropylene composite material, characterized in that, Prepared by the method described in any one of claims 1 to 7.

9. The application of the high-performance recycled polypropylene composite material of claim 8 in the preparation of automotive interior and exterior trim parts, automotive underbody panels, non-load-bearing components of battery packs, appliance housings, or power tool housings.

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