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基于小分子在聚合物中的扩散原理,采用液-固扩散法,将液态小分子交联剂、抗氧剂从固态低密度聚乙烯(LDPE)颗粒表面扩散到内部,实现小分子助剂与聚合物的均匀、温和混合,得到品质优良的可交联聚乙烯.采用DSC、FTIR等手段,分析不同扩散条件时LDPE颗粒表层和芯层的交联热焓、特征吸收峰强度的变化规律,探索小分子助剂向聚合物扩散的速率,获得优化的液-固扩散制备工艺条件.结果表明,扩散温度、扩散时间及助剂的分子结构是影响液-固扩散的主要因素;扩散温度为80℃时,经14 h扩散的LDPE颗粒芯层与表层的的交联热焓值基本相等,意味着交联剂已由LDPE颗粒表面扩散到内部,即已经得到混合均匀的可交联聚乙烯;而当扩散温度为60℃时,经24 h扩散的交联剂在LDPE颗粒中的分布也基本达到均匀.另一方面,经80℃扩散24 h后,聚乙烯颗粒芯层的抗氧剂DLTP含量与表皮层含量几乎相等;而相同扩散条件下,抗氧剂1076的扩散速率明显低于抗氧剂DLTP的扩散速率,且聚乙烯颗粒芯部抗氧剂1076含量仅为表层含量的1/2,其原因可能是抗氧剂1076分子较大,导致其扩散速率较小.
Based on the diffusion principle of small molecule in polymer, liquid small molecule cross-linking agent and antioxidant are diffused from the surface of solid low-density polyethylene (LDPE) particle by liquid-solid diffusion method, The results showed that the cross-link enthalpy and the characteristic absorption peak intensity of LDPE particles in different diffusion conditions were analyzed by means of DSC and FTIR, Explore the diffusion rate of small molecule additives to the polymer, and obtain the optimized preparation conditions of liquid-solid diffusion.The results show that the diffusion temperature, diffusion time and the molecular structure of additives are the main factors affecting the liquid- At 80 ℃, the enthalpy of cross-linking of LDPE particles core layer diffused for 14 h is almost equal to that of the surface layer, which means that the cross-linking agent has been diffused from the surface of LDPE particles into the interior, that is, a uniform cross-linked polyethylene ; When the diffusion temperature is 60 ℃, the cross-linking agent that has been diffused for 24 h also distributes uniformly in LDPE particles.On the other hand, after diffusion for 24 h at 80 ℃, the antioxidant of polyethylene particle core DLTP content and epidermal layer content The diffusion rate of the antioxidant 1076 is obviously lower than the diffusion rate of the antioxidant DLTP, and the content of the antioxidant core 1076 in the core of the polyethylene particle is only 1/2 of the surface layer, which may be due to the same diffusion condition Is a larger antioxidant 1076 molecules, resulting in a smaller diffusion rate.