Mengjie Jia,Yani Wang,Yiyang Qi,Xiaoge Ji,Zhongyuan Zhao,Shijing Sun
In the plywood industry, formaldehyde-based adhesives are commonly used, but the health risks associated with them are a significant concern. As a result, there has been a growing emphasis on developing formaldehyde-free alternatives. This study presents an eco-friendly adhesive formulated from vinyl acetate-ethylene (VAE) copolymer emulsion and polyvinyl alcohol (PVA). The synthesis conditions, curing behavior, synthesis mechanisms and curing mechanisms were further investigated. The optimal preparation conditions were as follows: VAE emulsion and 4 % PVA1788 were synthesized at 90 °C for 2 h, and the solid content was adjusted to 50 % by adding distilled water. Subsequently, 5 % pMDI was incorporated. The wet shear strength of the resulting adhesive, which is 0.93 MPa, met the requirements of the Chinese national standard GB/T 9846-2015 (≥0.7 MPa) for Class II plywood. The curing behavior of the VAE-PVA adhesive was investigated by measuring the insoluble mass proportion and thermal analysis. The results showed that when the adhesive was heated at 130 °C for 10 min, the insoluble mass proportion reached 81.16 %, and an endothermic reaction occurred at approximately 100 °C. To investigate the synthesis mechanism of VAE-PVA adhesive, FT-IR analysis revealed that esterification occurred between the VAE emulsion and the hydroxyl groups in PVA. Additionally, FT-IR analysis, XPS analysis, and Py-GC/MS analysis were used to explore the curing mechanism of the VAE-PVA adhesive. The results indicated that during the curing process, pMDI polymerized with the vinyl groups in the VAE emulsion and the hydroxyl groups in PVA, forming a three-dimensional network of cured polymer.
Butyl acrylate, methyl methacrylate, vinyl acetate and tertiary vinyl carbonate (VeoVa10) are the main monomers, and alkyl alcohol polyether sulfosuccinate monoester sodium salt (A-6820) and alkyl alcohol polyoxyethylene ether (EFS-900) are used as the emulsifiers. Vinyl triethoxysilane is used as the modified monomers. Potassium persulfate is the initiator. The silicon-modified polymer latex is prepared via the semi-continuous seeded emulsion polymerization. The structure of the latex film is characterized by Fourier transform infrared spectroscopy. Latex films are tested by the thermogravimetric analysis, differential scanning calorimetry and contact angle. The particle size of the latex is measured with the zetatrac dynamic light scattering instrument. The conditions for preparing the resultant latex is optimized and obtained as follows: the amount of emulsifier is 6 wt%; the amount of initiator is 0.4 wt% and the amount of VETS is 4 wt%. The appearance of the resultant latex is translucent and blue, and the average particle size of the polymer latex and its distribution is small. The water contact angle increased from 68.07 to 91.00 °. Thermal decomposition temperature of the film of the silicone-modified polymer latex is 16.17 °C higher than that of the film of conventional polymer latex.
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