Study On Modification Of Ethylene-Vinyl Acetate Rubber By Lithium Methacrylate And LaCl₃

The salts of unsaturated carboxylic acids are effective reinforcing agents for rubbers. In this dissertation, the reinforcement of ethylene-vinyl acetate rubber (EVM) by a salt of unsaturated carboxylic acid Lithium Methacrylate (LiMAA) was studied. The curing properties of EVM compounds, the mechanical properties and crosslinking structure of EVM vulcanizates were studied in detail. Then, effects of rare earth compound LaCl₃ on the EVM/LiMAA system were investigated. EVM/LiMAA/LaCl₃ system was compared with EVM/LiMAA system on curing properties, mechanical properties, crosslinking structure, aging resistance and electric properties. The mechanism of the effects were also explored.Firstly, through the neutralization of methacrylic acid (MAA) and LiOH, LiMAA was in situ prepared in EVM compound. The results showed that LiMAA had good reinforcing effects on EVM vulcanizates. The curing rates of EVM compounds were greatly accelerated with the increase of LiMAA content. The ionic crosslink density and gross density of EVM vulcanizates also obviously increased, and covalent crosslink density is the main part of the gross crosslink density. The effects of LiMAA content and LiOH/MAA mol ratio on the mechanical properties of EVM vulcanizates were studied. The formulation of 3.0 phr DCP, 30 phr LiMAA and LiOH/MAA mol ratio 1.0 is recommended for EVM vulcanizate with good mechanical properties. The tensile strength, tear strength and elongation at break are 30.9MPa, 93.4kN·m^-1 and 383%, respectively. Scanning Electronic Microscope (SEM) observation indicated that nanoscale particles disperse uniformly in EVM vulcanizates with the size ranging from 10¹ nm to 10² nm.Secondly, LaCl₃ was chosen as a modifier to the EVM/LiMAA system. When the LaCl₃ content was not more than 20 phr, the covalent crosslink density and gross density of EVM vulcanizates slightly decreased with the increase of LaCl₃ content, but ionic crosslink density increased. Ionic crosslink density became main part of the gross crosslink density when the LaCl₃ content was 20 phr. Mechanical properties of EVM vulcanizates decreased to some extent with the addition of LaCl₃. But after aging in air the EVM/LiMAA/LaCl₃ vulcanizate had much better maintenance of mechanical properties than EVM/LiMAA vulcanizate.The effect of LaCl₃ on electric properties of EVM/LiMAA vulcanizate was also researched. EVM vulcanizates can transfer from insulated to antistatic materials with addition of LaCl₃, volume resisitivity (Rv) of which can reach 3.00×10¹⁰Ω·cm. After moisture absorbing in the constant humidity environment, the Rv of EVM/LiMAA/ LaCl₃ vulcanizate decreased dramaticly with the increase of water-absorbing ratio. Rv of the EVM/LiMAA/ LaCl₃ vulcanizate reached 10⁴Ω·cm when the water-absorbing ratio was above 10%, which made the vulcanizate conductive. Fourier transform infrared spectroscopy (FTIR) and Nuclear Magnetic Resonance (NMR) tests showed that there were probably coordination bonds between La³⁺ and MAA-, which let Li⁺ transfer more freely and caused the enhancement of conductivity.