Triethyl citrate tec

Poly(3-hydroxybutyrate-co-4-hydroxyvalerate) with beta-hydroxyvalerate (HV) content of 5% (Y1000, purity of 98.8%) was obtained from Tianan Biologic Material Co., Ltd. (Ningbo, China). PVAc (BP-17s, partial alkalization PVA, PDI of 1.7, M_w of 84,000–89,000 according to manufacturer’s instructions), an amorphous polymer, was obtained from Chang Chun Petroleum Chemistry Co. Ltd. (Taipei, Taiwan). Tapioca starch (white powder containing 20 wt % amylose and 80 wt % amylopectin) was obtained from Hong Chi Co., Ltd. (Taipei, Taiwan). Glycerol (AR grade) and triethyl citrate (TEC) obtained from Sigma-Aldrich Co. (Taichung, Taiwan) were used as biodegradable plasticizers for PHBV, allowing them to act as internal plasticizers if grafted to the starch backbone or as monomers in repolymerization. MA, obtained from Sigma-Aldrich Co. (Taichung, Taiwan), helps promote bonding between the polyester and the natural starch via maleation. The enzyme solution (analytical reagent grade, obtained from Sigma-Aldrich Co. (Taichung, Taiwan)) had an activity of 0.35 mg/unit per min at pH 6.9 and 20 °C of soluble starch. The amylase obtained from human saliva (Sigma reference A0521) was at a concentration similar to that found in human blood plasma (50 U/L). 1 mL of calcium chloride was used to stabilize the solution.

The following polymer materials were used during film preparation: poly(L-lactide) (PLLA, Resomer® L214, MW = 650,000 g/mol, Boehringer Ingelheim Pharma, Biberach, Germany), poly(4-hydroxybutyrate) (P(4HB), MW = 450,000 g/mol, TephaFLEX®, Tepha Inc., Lexington, MA, USA), poly(ε-caprolactone) (PCL, MW = 80,000 g/mol, Capa™ 6800, Perstorp UK Limited, Warrington, UK). Furthermore, 10 wt% of Triethyl citrate (TEC, Sigma Aldrich, Munich, Germany) was added as plasticizer for the polymeric blend system PLLA/PCL.
Polymer films were prepared by a pouring process or manual dip-coating as described previously [55 (link),56 (link)]. The granules of the pure polymer types ((P(4HB), PCL and PLLA) or the polymeric blends (PLLA/P(4HB) 78/22 wt% and PLLA/PCL 70/20 wt%) were solved in chloroform. The solvent was allowed to evaporate from each sample for over 24 h, and then the samples dried for 1 day at 40 °C in a vacuum drying oven. The dried polymer films were 400 to 450 μm thick. Prior to in vitro testing, all films were sterilized by a common ethylene oxide sterilization process, aerated, and packed sterile.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate is a commercial product (PHBV, Ningbo City, China, TianAn Biopolymer: ENMAT Y1000) with 1 mol % HV 3-(hydroxyvalerate) content. Triethyl citrate (TEC, Burlington, MA, USA, Sigma Aldrich, Mw = 276.28 g·mol⁻¹, ρ = 1.137 g·L⁻¹) was used as a plasticizer. Winter rapeseed straw (RS) was collected as biomass waste from local farms Braslini, Pasiles and Susuri. RS were ground with a Retsch SM300 rotary grinder (Retsch GmbH, located in Haan, Germanya) a speed of 700 rpm using a 0.25 mm sieve. The obtained fibers were dried in an oven for 24 h at 60 °C and stored in closed plastic bags until further use. Sodium hydroxide pellets EMSURE were supplied by Sigma Aldrich (Sigma-Aldrich Chemie GmbH, located in Taufkirchen, Germany). A 50 wt % aqueous solution of NMMO was supplied by Merck (Biotecha Latvia, Riga, Latvia). Propyl gallate was purchased from Biosynth Carbosynth (Biosynth Carbosynth Ltd., located in Compton, Berkshire, United Kingdom).