The Graft Modification Of Low Density Polyethylene And Performance Research

Polyethylene is one of the common general plastic. But its application has been limited by its non-polarity. To improve its performance and expand the application range, Polyethylene often needs to be modified by the introduction of polar groups onto their backbones.Currently, the grafting degree (GD) is generally low owing to without reaction activity points of the Polyethylene’s molecular chain, usually less than2%, which is difficult to meet the application requirements. To further improve the GD and expand its scope of application, the low density polyethylene (LDPE) was grafted through solution approach with maleic anhydride (MAH) as grafted monomer. When dicumyl peroxide (DCP) was used as initiator, the effects of the concentration of initiator and monomer, reaction time and temperature, and the time for initiator dropping were investigated by the orthogonal experiment. The GD was determined by back-titration method. The results demonstrated that the optimum conditions are as follows:the concentration of initiator and monomer is4%and25%, the reaction temperature is130℃, the time for initiator dropping is0.5h and the reaction time is4h. The GD can be up to3.9%under this condition. Based on the research, the effects of the composite initiator system of BPO/DCP system and the oxidation-reduction system of BPO, DCP and N, N-Dimethylaniline on GD had been researched also. The result of composite initiator system shows that the best ratio of BPO and DCP is1:1. In that case, the concentration of initiator is4%, the concentration of MAH is25%, reaction temperature is130℃, reaction time is5h with adding BPO first, and the GD can be up to4.8%under this condition. The result of the oxidation-reduction system shows that the GD can be up to4.4%, when the concentrations of BPO and DCP both are2%, the addition dosage of DMA is0.4mL, the concentration of MAH is25%, reaction temperature is100℃and the reaction time is4h.The grafted copolymers (LDPE-g-MAH) were tested with FTIR, DSC and XRD. It shows that the maleic anhydride grafted onto the polyethylene macromolecular chains successfully. Compared with polyethylene, the crystallization peak shifted to a lower temperature, the crystallization activation energy decreased; the polyethylene crystal structure did not change with the introduction of polar group, but the crystal thickness, interplanar spacing and the crystallinity decreased. The crystallization behavior of the blend of LDPE-g-MAH with paraffin was studied by XRD. The result showed that the width of the crystal [110] and [200] were reduced with the addition of the LDPE-g-MAH, the crystal thickness and the crystallinity decreased as well. The new diffraction peaks in the spectra indicated that the co-crystallization occurred between paraffin and LDPE-g-MAH. The LDPE-g-MAH maybe has a potential influence on the pour point of heavy oil which is rich in paraffin. A preliminary study was made on the LDPE-g-MAH as a pour point depressant for heavy oil, and the result showed that it has some effects, but it is not obvious because of its low GD. So, the GD needs further improvement and deeper research.