Moification Of Fast-growing Poplar Wood By In-situ Polymerization And Cross-linking Reaction Mechanism

The aim of this research is to study the in-situ polymerization mechanism of wood modifier in wood. The influence of wood modifier on wood drying and rheological properties of modified wood were also studied in the paper. The wood modifier, AMU (Low molecular functional monomer) and urea, was impregnated into the fast grown wood by pulsed pressure impregnating machine. The drying process was complete including fast drying technology, hot-press drying technology, and heat-treated method. The changes of microscopic structure, mechanical properties, and chemical composition of modified wood after the three different treatments were discussed. The main conclusions are summarized as follows:(1) Water volatile was slower than the untreated wood in the drying process. The characteristics and quality of the modified wood attained Grade I according to Chinese Standard, while the unimpregnated wood just Grade II. Plasticity and tgδof modified wood was enhanced as the stress relaxation was reduced.(2) The impregnated wood drying with thickness of 5.5cm needed 130h with the initial temperature of 90℃and end temperature of 130℃. The drying quality was Grade I according to GB/T 6491-1999. It takes 100h for compression drying with compression rate at 21% and maximum pressure of 8MPa.(3) The air-dried density, over-dried density and basic density were improved 70%,71% and 41%, while 109%,83% and 74% with the compression rate of 21%. The bending strength, flexural elastic modulus, and compressive strength to grain increased by 59.9%,81.1%, and 40.2%, while 55.5%,93.4% and 71.0% for the compression wood. The 72h hygroscopy of unimpregnated wood was 116.6% while the impregnated wood was 76.2%. The 48h hygroscopy of unimpregnated wood was 123% while the impregnated wood was 91%.(4) The thermal stability increased as the AMU and urea increased. Oxygen index was also increased as result of the existence of wood modifier. As wood temperature increased during the drying process, chemical bonding was produced between wood and AMU (-OH) as result of in-situ polymerization between wood and AMU. SEM and EDXA showed that the transaction of unimpregnated and impregnated wood. The cell wall and vessels were filled with wood modifier and has been deformed by the compression during the drying process. The Nitrogen element was distributed in wood cell walls and intercellular spaces and the lumen. 13C NMR showed the crystalline structure of cellulose was not damaged, while the etherification reaction seemed occurred in the non-crystalline regions.(5) The section density distribution of modified wood was uniform. The transformation of wood cell and vessel were observed using SEM. The vessel appeared irregular polygon in the modified wood after hot-press drying process. The modifier particles distributed as rod-like or discontinuous in the wood cell. XPS showed that the oxidation occurred in the hemicelluloses, and etherification occurred between wood and wood modifier.(6) The weight loss of air-dried density, over-dried density and basic density were6.80%,4.37%, and 6.82%. The bending strength, flexural elastic modulus, and compressive strength to grain increased by 47.04%,36.72% and35.68%. The 72h hygroscopy of unimpregnated wood was 113.4% while the impregnated wood was 81.8%.