Morphology, Mechanical, and Water Barrier Properties of Carboxymethyl Rice Starch Films: Sodium Hydroxide Effect

Carboxymethyl rice starch films were prepared from carboxymethyl rice starch (CMSr) treated with sodium hydroxide (NaOH) at 10–50% w/v. The objective of this research was to determine the effect of NaOH concentrations on morphology, mechanical properties, and water barrier properties of the CMSr films. The degree of substitution (DS) and morphology of native rice starch and CMSr powders were examined. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) were used to investigate the chemical structure, crystallinity, and thermal properties of the CMSr films. As the NaOH concentrations increased, the DS of CMSr powders increased, which affected the morphology of CMSr powders; a polyhedral shape of the native rice starch was deformed. In addition, the increase in NaOH concentrations of the synthesis of CMSr resulted in an increase in water solubility, elongation at break, and water vapor permeability (WVP) of CMSr films. On the other hand, the water contact angle, melting temperature, and the tensile strength of the CMSr films decreased with increasing NaOH concentrations. However, the tensile strength of the CMSr films was relatively low. Therefore, such a property needs to be improved and the application of the developed films should be investigated in the future work.

Evaluation of Coatings to Improve the Durability and Water-Barrier Properties of Corrugated Cardboard

Recently, corrugated cardboard furniture gained interest from the market, yet is limited to indoor application. With an aim toward outdoor usage, water-barrier improvement of such products must be achieved. In this work, three commercially available coating grades (i.e., polymeric, mineral-filled polymeric, and hybrid silica sol-gel products) were spray-coated on corrugated cardboard using a facile, yet readily transferable, process. The investigation assessed the coating performance from the different drying conditions and natural UV-vis weathering effects, characterising their water absorption, hydrophobicity, coating morphology, and colour change. Results show a reduction in water absorption values (up to −98%) for both the polymeric coatings; instead, the hybrid sol-gel coating showed contact angles up to almost 150°. Generally, the SEM micrographs displayed some surface defects as well as good thickness homogeneity. A perceivable colour change occurred for each sample (CIEDE2000 up to 6.41), mainly occurring in the 0–100 h time range. This work provides promising results for the outdoor application of corrugated cardboard furniture.

The Study of Chitosan Solution Coating on Water Barrier Property of Seedling Paper Bag Made from Water Hyacinth

Seedling bags are low cost and light weight containers used by farmers to germinate and sprout seeds into seedlings before transplanting into the ground. However, cutting and removing seedling bags before the transplantation can damage the plant roots and cause losses in their productivity. In addition, plastics used in conventional seedling bags contribute to more plastic waste during this process. This study offers a solution to these problems with alternative biodegradable materials; i.e. modified papers made from an invasive alien aquatic plant species—water hyacinth—and enhanced with Chitosan solution coating. Papers were made from water hyacinth and dipped or sprayed with Chitosan solution in acetic acid at concentrations of 1% wt., 1.5% wt., and 2% wt. The dipping method showed better water barrier properties than the spraying method in every concentration, with 2% wt. concentration having the best barrier properties. The 2% wt. concentration of Chitosan coating by dipping method changed the water contact angle of the water hyacinth paper from a hydrophilic to a hydrophobic surface. This enhancement in water resistance was confirmed by water absorption time, which reached over 1.5 hours—3 times longer than the spraying method.