Studies On The Structure And Properties Of Silane Grafted And Crosslinked Polyethylene And Its Application In Polymer Nanocomposite

The dissertation simulates the diffusion of vinyl-silane in polyethylene employinglimited differentiation and studies the molten graft of the vinyl-silane and polyethylene.The Structure and property of silane grafted and crosslinked polyethylene is also studied interms of the theory of polymer elasticity. The study in the crystallization of silane graftedand crosslinked polyethylene is performed too from the angles of the crystal structure andcrystal dynamics. Both the HDPE/nano-SiO₂ composite and HDPE/nano-SiO₂organic-inorganic hybrid are made and their structures are proved. The structures andproperties of silane grafted and crosslinked polyethylene and its application in polymernanocomposite is studied systematically for the first time in the dissertation.The mathematical model is constructed in terms of finite differences. Then the specificcomputer program is compiled to simulate the diffusion of unsaturated silane inpolyethylene and diffusion coefficient is obtained to express the transmission of silane inpolyethylene. The activation energy of diffusion (E_D) can also be calculated. The E_D valuesof VTMS in HDPE, LDPE and LLDPE are 38.2,24.0 and 22.0KJ respectively.The existence of silane grafted polyethylene is characterized by FTIR,Raman,NMRand ICP. The particular absorbance peaks of-Si-O-CH₃ are found in FTIR spectrograph at1170cm^-1,1110cm^-1,1090cm^-1 and 960cm^-1. In Raman spectrograph, the scattering peak ofsilane shows up at 1090cm^-1. The resonance of -OCH₃ group appears atδ=4.25 andδ=68in ¹H and ¹³C NMR spectrographs. According to ICP, the percentage of VTMS grated toLLDPE, LDPE and HDPE turns out to be between 0.671-0.988%, 0.349-0.972% and0.254-750% respectively.The Mooney-Rivlin equation and the network state equation of cross-linked can beapplied to measure the density of cross-linkage of silane cross-linked polyethylene, whichis larger than that of peroxide cross-linked polyethylene when the content of gel is same.The above result can also be proved by the test of equilibrated dissolution and swell ofcross-linked polymer in dimethyl benzene at 70℃and boiled benzene. The parameter ofHuggins x1 in the system of LDPE and boiled benzene can be obtained at the same time,which is 0.31.DSC, XRD and Raman laser light scattering can be employed to study the structure change of the crystalline resulted from grafted and cross-linked polyethylene. Based onRaman spectrograph, with increasing amount of silane, the crystalline phase of silanegrafted LLDPE decreases from 57.58% to 46.99%, amorphous phase increases from11.58% to 16.52%, and the mesophase increases from 30.84% to 36.48%. The degree ofcrystallization based on DSC decreases from 40.73% to 32.32%, while XRD result showsthe percentage decreases from 39.66% to 32.87%. Furthermore, the melting point and thesize of the crystal decrease, while the distance between the surfaces of the crystalsincreases. Similar results have also been obtained with HDPE and LDPE. Thenon-isothermal crystallization kinetics indicates that the Avrami Index (n) of graftedpolyethylene barely changes, while the velocity constant of the crystallization (Z_c) dropsand the half-time of the crystallization (t₁₂) lengthens. After the cross-linking, Z_c dropsmore and t₁₂ lengthens more.Silane grafting to polyethylene and surface treatment of SiO₂ can both improve thecompatibility of HDPE/nano-SiO₂ composite and enhance the mechanics properties of thecomposites. When the amount of nano-SiO₂ is around 10%, the tension strength of thesystem increases by about 30% and the decomposing temperature increases by 20℃.PEW is employed as a model compound to study the Sol-Gel reaction of HDPE andTEOS. The Sol-Gel reaction of slane grafted polyethylene and TEOS is performed with asmall banbury mixer. When the amount of grafting monomer VTMS is below 2.0phr andthe added water is 20% of the amount of TEOS, a HDPE/SiO₂ organic-inorganic hybridwith good properties can be made if the banbury mixer runs at 60 min^-1. The tensionstrength of the hybrid can be improved by 30% and the decomposing temperature isincreased from 472.17℃to 476.68℃when the content of nano-SiO₂ is 0.99%. Both FTIRand XPS results can proved that a chemical bond is formed between nano-SiO₂ and themolecular chain of PE in the hybrid. TEM data also indicates that the SiO₂ particles aredispersed in the hybrid as 50-100 nm spheres.