The effect of microwave irradiation on poly(vinyl alcohol) dissolved in ethylene glycol

Abstract

Poly(vinyl alcohol) (PVA) dissolved in ethylene glycol is subjected to microwave (MW) irradiation for 1 h to determine possible degradation. Fourier transform infrared spectroscopy results show that MW treatment produces a minor effect on the solutions. Ultraviolet-visible spectroscopy suggests that PVA could undergoes loss of hydroxyl groups followed by formation of unsaturated conjugated bonds although the extent of degradation is limited, whereas size exclusion chromatography indicates that MW irradiation do not cause significant changes in PVA molar mass and neither chain cleavage nor crosslinking reactions are observed. Hence, polymer degradation induced by MWs in solution can be considered as negligible for prospective applications.

Effect of Microwave Irradiation on Polyvinyl Alcohol as a Carrier of Silver Nanoparticles in Short Exposure Time

“…As the time of microwave exposure increases, the absorbance of O-H stretch, C-H stretch, and CH 2 /CH 3 bend decreases. This reproduces the results in previous reports that PVA molecule undergoes elimination reaction and hydroxyl groups decrease [9,12]. Subsequently, some C-OH groups theoretically form double bonds C=O causing the reduction of CH 2 and C-H stretch, while some may lead to polymer dehydration with the formation of ether groups between PVA molecules, which is shown by the changes in peak around C-O stretch.…”

“…PVA is the product of the hydrolysis process of polyvinyl acetate. This means that the reaction may be incomplete leaving residual acetate groups [12]. Therefore, the changes at this peak may be the replacement of acetate group with ketone or aldehyde group.…”

“…However, they are thermally unstable. During the heat treatment, two major stages occur: elimination reactions and chain scission and cyclization [12]. Elimination reaction produces reactive carbon atoms along the polymer chain, which makes PVA highly reactive to other chemicals during the thermal process.…”

“…Compared with conventional heating, microwave heating is a more versatile and economical method with reduced reaction times [13]. Bernal et al investigated the effect of microwave on PVA with ethylene glycol as the solvent from 4 min to 60 min [12]. However, overexposure of microwave irradiation causes parching and total degradation of PVA.…”

Polymer Degradation Under Microwave Irradiation

“…In order to enhance the dissolution rate and to overcome the relatively poor solubility of highly hydrolyzed PVA, the solutions are sometimes are heated or even boiled. Bernal et al [62] has investigated the stability of PVA solutions under microwave irradiation in EG. FTIR, UV-vis and GPC measurements showed that only minor changes took place in PVA after the microwave treatment.…”