Tensile properties of alkaline lignin-poly vinyl alcohol film with formaldehyde crosslinker

Abstract: Industrial alkaline lignin-poly (vinyl alcohol) cross-linked film was prepared by casting. The effects of the dosage of industrial alkaline lignin, formaldehyde and the solution temperature, pH value and cross-linking time on the tensile properties of composites were investigated in a single factor experiment. Results showed that due to the cross-linking reaction, the viscosity of the cross-linked solution was higher than the blend solution. The optimum condition to prepare films of best mechanical properties was that the mass ratio of alkaline lignin (AL) and polyvinyl alcohol (PVA) 2:8, formaldehyde 8.8% of the dry matter, cross-linking time 40 min, the solution temperature 90℃, and pH 9. Incorporation of 20% alkaline lignin material into PVA improved the tensile properties of films. Under the best conditions, the elongation-at-break (EB) of neat PVA film and the AL-PVA cross-linked film was 205% and 236% respectively and the tensile strength (TS) was 52 and 46 MPa, respectively. The ATR-FTIR analysis showed that the cross-linking reaction between AL and PVA (1799) was present. Compared with neat PVA film, the tanδ magnitude and the Tg magnitude of AL-PVA reaction film were both decreased a little, which indicated that the addition of AL caused the increase in the distance between PVA molecules and the molecular mobility of the composite materials. The results have provided valuble information for design of the films.