木质素接枝共聚物改性低密度聚乙烯的性能

Performance study of low-density polyethylene modified by lignin graft copolymers

木质素是一种天然高分子材料,具有多种功能性,经常被应用于合成或其他天然高分子材料的改性领域。然而大量研究表明,极性的木质素与非极性的低密度聚乙烯(LDPE)不相容,直接利用木质素改性低密度聚乙烯会导致材料的力学性能受到负面影响。通过ARGET ATRP法将甲基丙烯酸月桂酯(LMA)接枝到木质素上,制备全生物质木质素接枝聚甲基丙烯酸月桂酯(OL-g-PLMA)共聚物,将LDPE和OL-g-PLMA按不同比例熔融共混制备LDPE/OL-g-PLMA材料。结果表明,木质素接枝PLMA后可以有效提高与低密度聚乙烯间的相容性,与添加未改性木质素(3.4%)相比,LDPE添加OL-g-PLMA共聚物(3.2%)的断裂伸长率和断裂能提高了1倍以上。SEM观察结果表明,木质素接枝PLMA后有助于提高其在LDPE基质中的分散性,从而增加两者之间的相容性。DMA测试也发现了OL-g-PLMA共聚物分子链与LDPE分子链之间存在相互作用,会限制LDPE分子链运动。在保证可见光高透过率条件下,添加OL-g-PLMA可以赋予LDPE薄膜阻挡紫外线的功能,并且使LDPE的氧气透过率下降40%。因此,LDPE/OL-g-PLMA具有良好的力学性能、抗紫外性能和阻隔氧气性能,在食品、医药包装行业有着一定的潜在应用价值。

Located in the cell walls of most plants,lignin is a renewable aromatic polymer and the second most abundant organic polymer in the plant kingdom after cellulose.It is a promising natural polymer material due to its low-cost and widely available.It can be copolymerized with small molecule monomers to produce thermoplastic polymers,and can also be applied in the field of modification for the synthesis or other natural polymer materials.However,extensive research has shown that the direct use of lignin-modified low-density polyethylene can have a negative impact on its mechanical properties due to the poor compatibility between non-polar LDPE and polar lignin.In order to solve the problem of poor compatibility between lignin and low-density polyethylene,the lignin molecules were modified by grafting functional monomers onto them,thereby altering their molecular chain structures and polarities to improve their compatibility with LDPE.The electron activators regenerated by electron transfer atom transfer radical polymerization(ARGET ATRP)method was used to graft a long-chain hydrophobic acrylate monomer(lauryl methacrylate(LMA)onto lignin,and a fully biomaterial lignin-graft-poly(lauryl methacrylate)(OL-g-PLMA)copolymer was prepared.Then LDPE/OL-g-PLMA materials were prepared by melting and blending LDPE and OL-g-PLMA in different proportions,and a series of tests were carried out.The mechanical test results showed that the elongation at break of LDPE was 119.0%,while the elongation at break of LDPE with unmodified lignin(3.4%)was 45%.When OL-g-PLMA copolymer(3.2%)was added to LDPE,the elongation at break and the fracture energy were more than doubled.It was suggested that lignin grafted PLMA improved its compatibility with low-density polyethylene.The results of SEM test displayed that the lignin grafted with PLMA improved the dispensability in the matrix of LDPE and the interfacial adhesion between them also increased.The results of DMA test demonstrated that there were interactions between molecular chains of LDPE and the grafted PLMA chains on the lignin,and the interactions further restricted the movement of molecular chains of LDPE.Furthermore,it was found that the addition of a small amount of OL-g-PLMA can provide LDPE film with the function of blocking ultraviolet light while ensuring high visible light transmittance,without weakening the mechanical properties of LDPE.Compared with LDPE individually,the addition of OL-g-PLMA can reduce the oxygen transmittance of LDPE by 40%.In general,the results suggest that LDPE/OL-g-PLMA films have good mechanical properties,UV resistance and low oxygen blocking properties,and therefore have potential application value in the food and medical packaging industry.This finding provides a pathway for lignin to be used in the modification and synthesis of resins as well as natural polymer materials.