Thermally Reversible Crosslinking Of Polyolefin Blends

Polyolefin products are widely used in production and daily life due to the advantages of low price,excellent performance and easy processing.Among them,polyethylene and polypropylene account for more than 50%.They have outstanding mechanical properties and water resistance,but due to their own structure,its heat resistance is poor,and its mechanical properties decrease severely when the temperature rises.The main method to solve this problem is to make them crosslinked.The formation of the cross-linked network can effectively improve the thermomechanical properties of the polyolefin products.However,the thermosetting polymers formed by chemical crosslinking will make the material unable to be processed again,resulting in huge pollution and waste.To solve this problem,this subject intends to introduce thermally reversible crosslinking agent dicyclopentadiene dicarboxylic acid(DCPDCA)to the ordinary polyolefins to form thermally reversibly cross-linked network,so as to ensure their mechanical properties and thermoplastic processability,and then realize the recycling of plastic products.Because of the lack of reaction sites,we blend ordinary polyolefins with epoxy polyolefins to form co-crystals in the crystalline region,and at the same time connect epoxy groups in the amorphous regions through chemical cross-linking,so as to improves its mechanical properties and heat resistance.The main research contents are as follows:1.The DCPDCA cross-linking agent is dissolved and blended with polyethylene glycol(PEG)to effectively improve the dispersibility of the cross-linking agent in the epoxy polyolefin matrix while reducing the particle size of the cross-linking agent.2.Exploration of the optimal reaction conditions for ring opening reaction between epoxy and carboxyl:through exploring the influence of different crosslinking agent dosage,different hot pressing temperature and hot pressing time on the mechanical properties of the sample,the best reaction conditions obtained are:DCPDCA:Epoxy=0.1,hot press at 150?for 2h.Through infrared characterization,determination of gel content and observation of tensile section,the occurrence of cross-linking reaction was verified,and a thermally reversible cross-linked epoxy polyethylene material with significantly improved mechanical properties was prepared.A control experiment with adipic acid as the cross-linking agent was carried out,and the tensile performance test and torque test were carried out on the samples after repeated processing,which verified the unique repeatability of the DCPDCA-epoxy polyethylene cross-linking system.3.The epoxy polyethylene and ordinary polyethylene are blended,and the DSC curve verifies the existence of co-crystals.Based on this,the effects of different blending ratios of epoxy polyethylene and ordinary polyethylene and the amount of crosslinking agent on the mechanical properties of the material are explored.And then the epoxy polyethylene-high/low crystallinity polyethylene cross-linked eutectic material was prepared.This material is reprocessable while the mechanical properties and heat resistance are significantly improved.Compared with ordinary polyethylene,the obtained epoxy polyethylene-low crystallinity polyethylene cross-linked eutectic material has increased its yield strength by 38%(9.3MPa to 12.8MPa),and its elastic modulus has increased by 65%(90MPa to 148MPa).The heat distortion temperature increased from 74? to 81?.The prepared epoxy polyethylene-high crystallinity polyethylene cross-linked eutectic material increased the yield strength by 18%(27.5MPa to 32.5MPa)compared with ordinary polyethylene.The elastic mold has increased by 16%(677MPa to 788MPa),and the heat distortion temperature has increased from 100? to 107?.