Assessment of starch-based wood adhesive quality by confocal Raman microscopic detection of reaction homogeneity

Confocal Raman microscopy (CRM) was used to detect the reaction homogeneity of vinyl acetate grafted on starch granules and help to assess the quality of high solid content starch-based wood adhesive (HSSWA). Primarily, four experimental starch samples were investigated, and by analysis of band area ratio (carbonyl/carbohydrate) of each granule, information about reaction homogeneity was collected. The results showed that reaction extent and homogeneity were inconsistent for samples with different G values, and the distribution of ester groups on blend samples was much less uniform than grafted starch samples with the same G value, confirming that CRM was useful for determining the homogeneity of chemical modification. Afterwards, the technique was applied to research HSSWA prepared by two-stage seeded polymerization and traditional process. The distribution of ester groups was more uniform among starch granules prepared by former method, resulted in adhesive with much better performance, indicating that uniformity of polymerization was an important factor related to properties of starch-based wood adhesive.