CN113913967A

CN113913967A - Preparation method of recycled polypropylene/polylactic acid high-strength composite material

Info

Publication number: CN113913967A
Application number: CN202111400956.7A
Authority: CN
Inventors: 夏茹; 张涛; 曹明; 独少培; 苗继斌; 杨斌; 徐程; 佀佳乐; 张潜
Original assignee: Anhui Tianlu New Material Co ltd; Anhui University
Current assignee: Anhui Tianlu New Material Co ltd; Anhui University
Priority date: 2021-11-24
Filing date: 2021-11-24
Publication date: 2022-01-11
Anticipated expiration: 2041-11-24
Also published as: CN113913967B

Abstract

The invention discloses a preparation method of a recycled polypropylene/polylactic acid high-strength composite material, which is characterized in that pentaerythritol tetraacrylate with high functionality is selected to graft and modify recycled polypropylene to obtain branched and modified rPP-g-PET4A, and the recycled polypropylene/polylactic acid composite material is prepared based on a two-step method. Compared with the prior art, after the graft modification of the recycled polypropylene, on one hand, the invention changes the polarity of the recycled polypropylene and increases the compatibility between the recycled polypropylene and the polylactic acid; on the other hand, based on the volatility of the melt index of the recycled polypropylene raw material, the melt index range of the recycled polypropylene is regulated and controlled through controllable grafting, and the requirement of the subsequent drawing process of the composite material is met after the recycled polypropylene is blended and extruded with the drawing-grade polylactic acid. The prepared recycled polypropylene/polylactic acid composite material has improved tensile strength and impact strength to different degrees, and the method is simple, convenient and quick in reaction and has wide application prospect.

Description

Preparation method of recycled polypropylene/polylactic acid high-strength composite material

Technical Field

The invention relates to a preparation method of a high-strength composite material of recycled polypropylene/polylactic acid, which is characterized in that rPP/PLA is compatibilized by grafting copolymerization of pentaerythritol tetraacrylate and recycled polypropylene.

Background

The plastic products commonly used in daily life are made of polypropylene, polyethylene, synthetic resin, synthetic fiber and the like. These are all without exception of extremely strong non-degradability, and the mass production of plastics poses a great crisis to the world environment. In recent years, with the concern of environmental issues, degradable polymer materials having excellent properties have attracted great attention in academic and industrial fields. Polylactic acid (PLA) as a green degradable material is advocated under the current increasingly severe background of 'white pollution', but the application of the PLA is severely limited by the defects of low crystallization rate, large brittleness and the like.

The melt blending of the waste and old recycled polypropylene and the wire-drawing polylactic acid is expected to improve the toughness of the PLA and the strength of the composite material, and can realize the partial degradation of the composite material, so that the composite material is environment-friendly. But because the polarity difference between PLA and PP is large, the compatibility is not good, and the interfacial bonding force of the composite material after blending is poor. Only by effectively improving the two-phase compatibility of PP and PLA through the interface compatibilization technology, the comprehensive performance of the composite material can be obviously improved.

Disclosure of Invention

Aiming at the technical problems, the invention provides a preparation method of a high-strength composite material of recycled polypropylene/polylactic acid. The invention selects high-functionality pentaerythritol tetraacrylate to graft and modify polypropylene to obtain a polypropylene material rPP-g-PET4A containing a branched structure, which is used for preparing a recycled polypropylene/polylactic acid composite system and is used for preparing a high-strength environment-friendly degradable plastic material for an outdoor plastic fence net by drawing wires. Compared with a simple blending system of the recycled polypropylene and the polylactic acid, the modified recycled polypropylene/polylactic acid composite material has improved tensile strength and impact strength to different degrees. The method is simple, convenient and quick in reaction, and has wide application prospect.

The preparation method of the high-strength composite material of the recycled polypropylene/polylactic acid comprises the following steps:

step 1: using dicumyl peroxide as an initiator, and initiating recovered polypropylene and pentaerythritol tetraacrylate (PET4A) to graft by using generated free radicals under the heating condition to obtain graft modified polypropylene rPP-g-PET 4A;

step 2: weighing 140g of the graft modified polypropylene obtained in the step 1, uniformly mixing with 60g of pre-dried (dried at 80 ℃ for 12h) wire-drawing polylactic acid (PLA), adding the mixture into a conical double screw with the temperature of 200 ℃ and the rotating speed of 30r/min for extrusion, obtaining a sample strip through water cooling, granulating, and drying in an oven with the temperature of 80 ℃ for 12h to obtain the modified recycled polypropylene/wire-drawing polylactic acid high-strength composite material.

In step 1, the initiator is peroxide, preferably dicumyl peroxide.

In the step 1, the dosage ratio of the recycled polypropylene, the pentaerythritol tetraacrylate and the initiator is 200 g: 2-10 g: 0.1 g.

In the step 1, the preparation of the graft modified polypropylene specifically comprises the following steps:

the recovered waste polypropylene is dried in a drying oven at 80 ℃ for 12 hours in advance. Weighing 200g of recycled polypropylene, and premixing 2g of PET4A (1 wt%) and the recycled polypropylene uniformly in a big plastic cup by using a glass rod; weighing 0.1g of DCP (0.05 wt%), grinding into powder, adding the DCP powder into recycled polypropylene and PET4A, and mixing uniformly; and adding the mixture into a conical reverse double screw with the temperature of 200 ℃ and the rotating speed of 30r/min, extruding, cooling by water to obtain a sample strip, cutting into particles, and drying in an oven with the temperature of 80 ℃ for 12 hours to obtain the graft modified polypropylene rPP-g-PET 4A.

In step 1, the melt index of the recycled PP is in the range of 5.0 to 11.0g/10min (230 ℃/2.16 kg).

In step 2, the melt index range of the wiredrawing grade polylactic acid is 3.0-10.0g/10min (190 ℃/2.16 kg).

In the step 2, the feeding mass ratio of the graft modified polypropylene to the wiredrawing grade polylactic acid is 7: 3.

The melt index of the drawing grade polypropylene is usually 2-5 g/10min, and the melt index of the drawing grade polylactic acid is 30.0-60.0g/10min (210 ℃/2.16 kg). The melt index of the recycled polypropylene is mostly 5-11g/10min, for example, the melt index of the recycled polypropylene in the embodiment is 9.86g/10min, and the recycled polypropylene can not meet the wire drawing requirement when being used alone or compounded with polylactic acid (7: 3). The rPP-g-PET4A modified by the method can be controlled within the range of 1.0-2.0g/10min, and the ratio of the rPP-g-PET to the wiredrawing grade polylactic acid is 7:3 the wire drawing performance requirement can be met after the composition.

After the recycled polypropylene is grafted and modified, on one hand, the polarity of the recycled polypropylene is changed, and the compatibility between the recycled polypropylene and polylactic acid is increased; on the other hand, based on the volatility of the melt index of the recycled polypropylene raw material, the melt index range of the recycled polypropylene is regulated and controlled through controllable grafting, and the requirement of the subsequent drawing process of the composite material is met after the recycled polypropylene is blended and extruded with the drawing-grade polylactic acid.

The outdoor plastic fence net for the farmers at present is prepared by drawing and preparing multi-purpose recycled PP, and has poor strength and aging resistance. The composite material prepared by the preparation method has improved strength and aging resistance, can be recycled and has certain degradability. Can be used for outdoor plastic fence nets, can be expanded to be used in the fields of special coke nets for railway transportation with higher performance requirements and the like

Compared with the prior art, the invention has the beneficial effects that:

the invention utilizes pentaerythritol tetraacrylate and recycled waste polypropylene to graft the pentaerythritol tetraacrylate onto a polypropylene molecular chain under the heating initiation of dicumyl peroxide, so as to form modified recycled polypropylene (rPP-g-PET4A), and tests show that the tensile strength is obviously improved, the impact strength is also improved to a certain extent, and the composite material with excellent mechanical properties is obtained.

Drawings

FIG. 1 is a schematic diagram of a preparation mechanism of the pentaerythritol tetraacrylate grafted to a molecular main chain of the recovered polypropylene and then melt-blended with polylactic acid under the heating initiation of dicumyl peroxide.

FIG. 2 is a Fourier infrared spectrum of the modified composite material at 1757cm^-1The peak at wavenumber for carbonyl C ═ O appears, indicating that PET4A was grafted onto the molecular chain of the recycled PP.

FIG. 3 is a stress strain curve for recycled PP/PLA and pentaerythritol tetraacrylate modified PP/PLA.

FIG. 4 is a scanning electron micrograph of a recovered PP/PLA mass ratio of 7/3.

FIG. 5 is a scanning electron microscope image of pentaerythritol tetraacrylate modified recycled PP/PLA mass ratio of 7/3 (rPP-g-2% PET 4A/PLA-7/3).

Detailed Description

The technical solution of the present invention is further described in detail by the following specific examples, which are implemented on the premise of the technical solution of the present invention, and detailed embodiments and specific operation procedures are given, but the scope of the present invention is not limited to the following examples.

In the following examples, the mechanical properties were measured: and crushing the extruded sample, setting the processing temperature to be 220-205-200 ℃ by using an injection molding machine, and performing injection molding to obtain a dumbbell-shaped sample strip, wherein the sample type 1BA meets the national standard GB/T10403-2006. The tensile rate is 50mm/min, a sample with the length of 80mm, the width of 10mm and the cutting length of 4mm is cut by a micro injection molding machine, the test sample with the residual 6mm is cut, a pendulum impact tester is used for carrying out impact test at room temperature, and the test of the notch impact performance of the cantilever beam refers to the GB/T1843-2008 standard test.

Example 1:

1. the recovered polypropylene was modified to graft pentaerythritol tetraacrylate onto the polypropylene.

Recovered waste PP was dried in a drying oven at 80 ℃ for 12 hours, 200g of PP was weighed, 1 wt% PET4A (2g) and recovered PP were premixed in a large plastic cup with a glass rod, then 0.05 wt% DCP (0.1g) was weighed, the DCP was ground to a powder, and the powder was uniformly premixed in recovered PP and PET 4A. And then placing the premixed material into a conical twin-screw with the temperature of 200 ℃ and the rotating speed of 30r/min for extrusion, obtaining a sample strip through water cooling, cutting short, and drying in an oven with the temperature of 80 ℃ for 12 hours to obtain the graft modified polypropylene (rPP-g-PET 4A).

2. The modified recycled polypropylene and the polylactic acid are melted and blended

Weighing 140g of the graft modified polypropylene obtained in the step 1, weighing 60g of polylactic acid (PLA) dried in an oven at 80 ℃ for 12h, then premixing the two polymers uniformly, then putting the premixed material into a conical twin-screw with the temperature of 200 ℃ and the rotating speed of 30r/min for extrusion, obtaining a sample strip through water cooling, cutting the sample strip, and drying in the oven at 80 ℃ for 12h to obtain the recycled polypropylene/polylactic acid high-strength composite material.

Example 2:

Recovered waste PP was dried in a drying oven at 80 ℃ for 12h, 200g of PP was weighed, 2 wt%, 3 wt%, 5 wt% PET4A (4g, 6g, 10g) and recovered PP were premixed in a large plastic cup with a glass rod, then 0.05 wt% DCP (0.1g) was weighed, DCP was ground to a powder, and then the powder was uniformly premixed in recovered PP and PET 4A. And then placing the premixed material into a conical twin-screw with the temperature of 200 ℃ and the rotating speed of 30r/min for extrusion, obtaining a sample strip through water cooling, cutting short, and drying in an oven with the temperature of 80 ℃ for 12 hours to obtain the graft modified polypropylene (rPP-g-PET 4A).

Weighing 140g of the graft modified polypropylene obtained in the step 1, weighing 60g of polylactic acid (PLA) dried in an oven at 80 ℃ for 12h, then uniformly premixing the two polymers in a large plastic cup, then putting the premixed material in a conical reverse twin screw with the temperature of 200 ℃ and the rotating speed of 30r/min for extrusion, obtaining a sample strip through water cooling, and drying in the oven at 80 ℃ for 12h after cutting into particles to obtain the recycled polypropylene/polylactic acid high-strength composite material.

Table 1 shows the tensile and impact strength test results for recycled PP/PLA and modified recycled PP/PLA. After 2% pentaerythritol tetraacrylate is modified and the recovered PP and PLA are melted and blended, the composite material has the best comprehensive performance, and the tensile strength is increased by 6.89 MPa. The impact strength is increased by 5.49KJ/m²。

TABLE 1

TABLE 2

Table 2 shows the results of melt index testing of three different mass ratios (6: 4, 7:3, 8: 2) of rPP, rPP-g-2% PET4A and rPP-g-2% PET 4A/PLA.

Based on the experimental data in tables 1 and 2, the flowability (melt index) and mechanical properties (tensile strength, elongation at break) are considered comprehensively, and the composite material of modified rPP-g-PET4A/PLA is selected to be 7:3, the material can meet the requirement of a wire drawing process for preparing the plastic fence net, and the comprehensive properties of the material strength and toughness are optimal.

FIGS. 4 and 5 are SEM comparison of recycled PP/PLA and modified recycled PP/PLA composites, respectively, wherein FIG. 4 is a view of recycled PP/PLA. The dispersed phase is PLA, the particle sizes are different and are not uniformly distributed, which shows that the compatibility of the PLA and the two phases of the recycled PP is poor, and the modified recycled PP/PLA composite material is shown in figure 5 that the dispersed phase PLA is uniformly distributed, wherein the particle sizes are distributed in the dispersed phase PLA and are larger, the larger the particle size of the dispersed phase is, the larger the tensile strength of the dispersed phase is, which shows that the compatibility of the graft-modified recycled polypropylene and the two phases of the polylactic acid is better, so that the comprehensive mechanical property of the composite material is improved.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. A preparation method of a high-strength composite material of recycled polypropylene/polylactic acid is characterized by comprising the following steps:

the high-functionality pentaerythritol tetraacrylate is selected to graft and modify the recovered polypropylene to obtain polypropylene containing an rPP-g-PET4A branched structure, and the recovered polypropylene/polylactic acid composite material is prepared based on a two-step method so as to improve the tensile strength and the impact strength of the composite material.

2. The method of claim 1, comprising the steps of:

step 1: under the condition of heating, initiating the recovered polypropylene and pentaerythritol tetraacrylate by using free radicals generated by an initiator to carry out grafting reaction, thus obtaining pentaerythritol tetraacrylate graft modified polypropylene rPP-g-PET 4A;

step 2: weighing the graft modified polypropylene obtained in the step 1, uniformly mixing the graft modified polypropylene with pre-dried wiredrawing-grade polylactic acid, adding the mixture into a conical double screw with the temperature of 200 ℃ and the rotating speed of 30r/min for extrusion, obtaining a sample strip through water cooling, and drying the sample strip in an oven with the temperature of 80 ℃ for 12 hours after cutting the sample into granules to obtain the recycled polypropylene/polylactic acid high-strength composite material.

3. The method of claim 2, wherein:

in the step 1, the initiator is dicumyl peroxide.

4. The method of claim 2, wherein:

5. The production method according to claim 2, 3 or 4, characterized in that:

6. The method of claim 5, wherein:

weighing 200g of pre-dried recycled polypropylene, and premixing 2g of pentaerythritol tetraacrylate and polypropylene uniformly; grinding 0.1g of initiator into powder, adding the powder into recycled polypropylene and pentaerythritol tetraacrylate, and uniformly mixing; and adding the mixture into a conical double screw with the temperature of 200 ℃ and the rotating speed of 30r/min for extrusion, obtaining a sample strip through water cooling, cutting into particles, and drying in an oven with the temperature of 80 ℃ for 12 hours to obtain the graft modified polypropylene rPP-g-PET 4A.

7. The method of claim 2, wherein:

in step 2, the melt index of the wiredrawing grade polylactic acid ranges from 30.0 to 60.0g/10min (210 ℃/2.16 kg).

8. The method of claim 2, wherein: