Performance study of low-density polyethylene modified by lignin graft copolymers
Located in the cell walls of most plants,lignin is a renewable aromatic polymer and the second most abun-dant 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 poly-mers,and can also be applied in the field of modification for the synthesis or other natural polymer materials.How-ever,extensive research has shown that the direct use of lignin-modified low-density polyethylene can have a nega-tive 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 po-larities to improve their compatibility with LDPE.The electron activators regenerated by electron transfer atom trans-fer 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 dispen-sability 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.Com-pared 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 in-dustry.This finding provides a pathway for lignin to be used in the modification and synthesis of resins as well as natural polymer materials.
ligninlow density polyethyleneOL-g-PLMAcompatibilitymechanical property
万方数据
维普
