Enhanced Dimensional Stability of Straw-based Biocomposites Modified with UV Light-cured Coatings

This study demonstrated an effective method to enhance the dimensional stability of straw-based biocomposites with modified lignosulfonate as a binder. The ultraviolet (UV) light-curable nanosol was prepared by adding 3-(trimethoxysilyl)propyl methacrylate (MEMO) as sol–gel precursor into polyvinyl alcohol (PVA) solution. The MEMO/PVA coatings were generated using 2-hydroxy-2-methyl-1-phenylpropan-1-one (Darocur 1173) as radical photo-initiator and chitosan (CS) as additive, on straw-based biocomposites via UV-curing process. The effects of the crucial steps, such as the UV-curing process, hydrolysis time, Darocur 1173 dosage, and CS dosage on the dimensional stability of straw-based biocomposites, were evaluated. The optimum preparation parameters, obtained using the Box–Behnken design, were 31.9 min hydrolysis time, 4.5% Darocur 1173 dosage, and 2.7% CS dosage. Moisture resistance of minimum TS of CS-MEMO/PVA-coated straw-based biocomposites resulted in ~23.1% reduction in dimensional stability without significant decline in the mechanical properties when compared with those without UV curing. Moreover, the glossy spherical particles underwent arrangement in a fish-scale shape with scales closely linked with each other and no agglomeration occurred in CS-MEMO/PVA hybrid film. The CS promoted the cross-linking of MEMO/PVA coating on the biocomposite surface. The resulting biocomposites can be directly applied to public humid-environment applications such as bath furniture and bathroom partitions.