| The lignin-based polyurethane (PU) films were prepared from wheat straw alkali lignin bysolution casting with polyethylene glycol (PEG) and polymeric phenyl methane-diisocyanate(PAPI) in the solvent of N,N-dimethylformamide (DMF). The optimum technology to preparePU, the influence factors of PU performance including NCO/OH ratio, alkali-lignin content,PEG molecular weight and the ratio of polyethylene glycol moleculars of different chain lengthwere studied respectively. The results showed that changing the molar ratio of PEGs ofdifferent molecular weight in the system of reaction could enhance the tear resistance behaviorof PU films outstandingly. The Young's modulus, tensile strength, elongation at break and tearresistance were 1.49 GPa, 36.5 Mpa, 12.7% and 8460mN, respectively, under the condition ofNCO/OH ratios of 2.5 and 20 percent lignin content with the ratio of 2 for PEG1000 toPEG300.The glass transition temperature (Tg) and thermal degradation behavior were examined byDSC and TGA. The O-Methoxyphenol, 3-Methoxy-4-hydroxybenzaldehyde and 3-Methoxy-4-hydroxy cinnamic acid, which have the same structure to lignin, were selected as the modulesubstances to study on the reaction between Alkali-lignin and polymeric phenyl methane-diisocyanate by the means of Infra-red (IR) spectrum and High Pressure Liquid Chromatogram.The thermal-oxidation, UV photolysis and hydrolysis behaviors of straw alkali ligninpolyurethane films (PUF) were tested respectively. The results show that the retain ratio oftensile strength of thermal-oxidation samples with 20% lignin enhanced from 89.3% to 132.0%comparison with pure PUF and which of elongation at break from 19.3% to 66.3%. After thesamples exposing in UV aging instrument for 28 d, their elongation at break with 20% ligninwas 48.6%, better than 9.4% of controlling ones. After hydrolysis lignin PUFs retain 95.5% oftheir strength, while lignin free ones retain 25.2% of their strength. However, the adding ofalkali-lignin greatly reduced the alkali resistance ability of PUF. |
