Abstract
The impact of hydroxypropylsulfonation/caproylation on the adhesion of cornstarch to polylactic acid (PLA) fibers was investigated for ameliorating the applications such as PLA sizing. The hydroxypropylsulfonated and caproylated cornstarch (HCS) samples with different degrees of substitution (DS) were synthesized by a hydroxypropylsulfonation of acid-converted cornstarch (ACS) with 3-chloro-2-hydroxy-1-propanesulfonic acid sodium salt (CHPS-Na) and subsequently a caproylation with caproic anhydride (CA). The HCS granules were characterized by Fourier transform infrared spectroscopic and scanning electron microscopy. The adhesion was evaluated by measuring the bonding forces of the PLA roving impregnated. The mechanical behaviors of the adhesive layers were estimated by determining the properties of the films. The results of adhesion measurement were also analyzed especially through the wetting and spreading of the paste on the fiber surfaces, as well as the failure type, internal stress and mechanical behaviors of the adhesive layers among fibers. Additionally, apparent viscosity and its stability of the pastes were also determined. It was found that hydroxypropylsulfonation/caproylation was not only able to obviously improve the adhesion of ACS to PLA fibers, but also capable of further improving the adhesion of hydroxypropylsulfonated starch (HS) to the fibers. With the rise in the total DS, the adhesion gradually increased. The two substituents improved the wetting and spreading, reduced the internal stress, lowered the probabilities of interfacial failure and cohesive failure, decreased the film brittleness, and increased the van der Waals force at the interfaces. Moreover, the HCS samples with a stability of above 85% could meet the demand on the stability for sizing. Considering the experimental results of the adhesion and the analysis of the results, HCS showed potential in the application of PLA sizing.
Highlights
Starch is described as one of the most abundantly occurring natural polymers [1]
hydroxypropylsulfonated starch (HS) (DS = 0.029), indicating hydroxypropylsulfonation/caproylation was able to improve and HS (DS = 0.029), indicating hydroxypropylsulfonation/caproylation was able to improve the adhesion of starch to polylactic acid (PLA) fibers, and able to further improve the adhesion compared with the adhesion of starch to PLA fibers, and able to further improve the adhesion compared with the HS
The adhesion of hydroxypropylsulfonated and caproylated cornstarch (HCS) to PLA fibers was correlated with the total degrees of substitution (DS), and the forces gradually the HS
Summary
Starch is described as one of the most abundantly occurring natural polymers [1]. It consists of both polymers known as amylose and amylopectin, which possesses a large number of α-d-glucose units connected through α-1, 4 linkages and α-1, 6 linkages [2]. The alteration of adhesion behavior and the toughness of starch film produced by the introduction of substituents through chemical modification have received an increasing amount of attention recently. An excessive increase in the introduction of the hydrophobic substituents can reduce the water-dispersibility and adversely affect the adhesion of starch to fibers since the paste applied for sizing warps is only a water-based adhesive. As a result, improved adhesion of starch to PLA fibers and a lowered brittleness of starch film may be expected, after the introduction of the PSH substituents and caproates. For these reasons, hydroxypropylsulfonation and caproylation were employed to derivatize the starch in this work.
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