Effect of reaction conditions and alkyl chain lengths on the properties ofhydroxyalkyl starch ethers

Starch applications in the plastics industry have been investigated intensi vely for many years. Unfortunately, native starch is unsuitable for most ap plications in polymers, because of its hydrophilic and brittle character. M odification of native starch can be a solution of this problem. In our research programme we developed an environmentally friendly process for the preparation of starch derivatives with long hydrophobic side chains based on natural products derived from vegetable fats and oils on the one hand and amylomaize starch on the other hand. In this process modification is carried out by the addition of long-chain 1,2-epoxyalkanes (chain length s varying between 6-18 C atoms) to starch in an alkaline aqueous medium. Re action yields and molar degrees of substitution depended on chain length, r eaction time, temperature and catalyst concentration. Under optimised react ion conditions molar degrees of substitution of hydroxyalkyl starch ethers for theoretical molar substitution (MS) = 3.0 decreased from MS=1.8 (C-6 st arch ether) to MS=0.2 (C-18 starch ether), respectively. Hydrophobic proper ties of starch products were measured in order to reveal structural effects obtained at different reaction conditions. Water solubility and water abso rption properties of hydroxyalkyl starch ethers decreased with increasing c hain length and number of hydroxyalkyl substituents. Thermal and thermoplas tic properties of starch ethers were investigated in order to determine the ir potential use as biodegradable polymers in the plastics industry. As exp ected, thermoplasticity of starch ethers increased with increasing MS and i ncreasing chain length of the hydroxyalkyl side groups.