Wood Polymer Composites Prepared From Fast Growing Species With The Urea-Formaldehyde Resin

It was fond of people for preparing poplar wood to wood polymer composites because of its natural features and high useful values. However, it was very difficult to adjust the price of wood polymer composites to adapt them market competition as its expensive cost and low performance. So, the min aim of the research was to improve the general property of wood polymer composites by the following thoughts.Wood polymer composites were prepared successfully by vacuum impregnation method when poplar is chosen as the matrix and urea-formaldehyde resin oligomers as the infill. The permeability of the prepolymers into wood was proved by a small amount of water-soluble dye; moreover, impregnation yield, weight percentage gain, dimensional stability, compressive strength, bending strength of wood polymer composites was tested. Using FTIR and SEM to analysis the real relationship between the performance of wood polymer composites and the inner structure, and to find the basic reason why the capability of wood polymer composites was enhanced. The objective of this research is to improve physical and mechanical properties of poplar of the growing species, to increase the added value, and to extend application field of low density poplar. The main research results of this dissertation are as follows:(1) The synthesis process of urea-formaldehyde resin prepolymers was alkali-acid-alkali, Urea divided into three times (mass ratio 4:5:1) was added during the synthesis process of urea-formaldehyde resin prepolymers. FT-IR analysis of urea-formaldehyde resin:the strong peak at 3435 cm-1 is assigned to the stretching vibration of hydroxyl groups and N-H bond, and the weak absorption peak at 2924 cm-1 is attributed to the C-H stretching vibration of methylene (-CH2-) groups. The appearance of the stronger peak at 1637 cm-1 attributed to amide groups indicate that the amido groups in urea have participated in the synthesis reaction. The absorption peak at 1050 cm-1 is assigned to the stretching vibration of C-O bond in ether (CH2-O-CH2) groups; it was proved that the synthesis of prepolymers is urea-formaldehyde resin; the solid content of urea-formaldehyde resin oligomers was about 55%.(2) The viscosity of prepolymers was tested at different temperatures by use of Tu-4 cup viscometer. The optimum process temperature was at 30℃during the preparation of wood polymer composites. The permeability of the prepolymers into wood was proved by a small amount of water-soluble dye. (3) Impregnation yield, weight percentage gain of wood polymer composites increased by 195%,96%, respectively. To obtain the satisfactory impregnation yield and weight percentage gain, the urea-formaldehyde resin oligomers should have good mobility at 30℃.(4) The FT-IR analysis of wood polymer composites demonstrate that the functional groups of poplar and the urea-formaldehyde resin reacted, the skeleton structure of cellulose and lignin was changed. So, the performance of poplar was increased.(5) The water uptake of poplar and wood polymer composites was 126.9% and 53.3%, respectively, water repellency efficient of wood polymer composites was 58.0%; Swelling of poplar and wood polymer composites was 11.4% and4.6%, respectively, water repellency efficient of wood polymer composites was 59.6%.(6) Horizontal compression strength of poplar and wood polymer composites was 19.5 MPa and 39.5 MPa, respectively; longitudinal compression strength of poplar and wood polymer composites was 7.2 Mpa and 9.9 Mpa, respectively. Bending strength of poplar and wood polymer composites was 120.6 MPa and 147.5 MPa. Horizontal and longitudinal compression strength and bending strength increased 37.5%,102.6% and 22.3%, respectively.(7) Scanning Electron Microscopy (SEM) analysis of poplar and wood polymer composites indicated that the urea-formaldehyde resin in wood polymer composites filled up the wood cell lumina in a solid form. The urea-formaldehyde resin oligomers have low viscosity; what's more, the viscosity of the urea-formaldehyde resin oligomers reduces and has good mobility when heating.