Effect of Valley Beater Refining on Tensile Properties of Molded Pulps from Rice Straws

Abstract

Rice straw, an abundant agricultural waste, is shown to be a promising resource for pulp and paper packaging manufacturing. In this study, rice straw pulps or cellulose fibers were extracted using a soda-AQ process and then the rice straw pulp slurries were refined by a Valley beater. The effect of refining time (15-60 min) on the pulp fiber characteristics was studied. It was found that both initial fiber length and width were decreased with refining time. The refined fibers became fibrillated, finer, and also more uniform in size confirmed by SEM. The pulp freeness (CSF) was reduced with increasing refining time as expected due to higher water-holding capacity of more fibrillated pulps. Then, the molded sheets were formed from the prepared rice straw pulps and examined. From tensile testing, the results indicated that the tensile properties of the molded sheets from the refined pulps were significantly enhanced (p < 0.05), thanks to an increase in fibrillated fiber surface area and inter-fiber bonding degree. The Valley beater refined rice straw pulp provided the molded sheet with the highest tensile index of 51.96 ± 4.08 Nm/g which are comparable to that of the sheets prepared from PFI mill refining process. The tensile properties of the current refined sheets were also in the acceptable range for typical commercial molded pulp packaging. In addition, the freeness values of the optimal Valley beater refined pulps are relatively high (348-423 ml), implying a benefit in forming process and manufacturing of pulp products.

Molded pulp products for sustainable packaging: Production rate challenges and product opportunities

“…Considerable research attention has been focused on the potential usage of nonwood fibers. These have included sugarcane bagasse (Jeefferie et al 2011;Waranyou 2014), various types of straw (Curling et al 2017;Hart 2020;Prasertpong et al 2021), invasive grass (Chen et al 2012), hemp (Buxoo and Jeetah 2020), and mycelium (fungal biomass) (Abhijith et al 2018). As the price of global wood pulp is rising and the advancement of electronic media are decreasing the recycling of fibers from paper waste, the demand of alternative sources of raw material for creating the molded pulp packages has been continually increasing (Gouw et al 2017;Johnston 2016).…”

“…Nevertheless, refining can be a straightforward way to achieve the strength specifications, including the elastic modulus values needed for different molded pulp products. For example, Prasertpong et al (2021) judged that a freeness value in the range 348 to 423 mL would give suitable tensile properties in typical cases when refining delignified rice straw. Such numbers represent a relatively low level of refining treatment.…”