Research On Manufacturing Of MDF From Rice And Wheat Straws With Modified UF Resin And Pretreated Straw

Due to the particularities of raw materials and the surface substances which inhibit water-based resin bonding, medium density fiber boards (MDFs) from rice straw and wheat straw bonded with conventional urea-formaldehyde resin (UF) do not have satisfactory properties as required, and commercial production line of those kinds of MDFs has not been built yet in China., In order to provide some theoretical foundation for manufacturing MDFs from rice and wheat straw, this research work dealt with the manufacturing optimization, performance modification and structure of the environment-friendly UF resin, investigated the influences of straw pretreatment both with chemicals and biology enzymes on the properties of the straw fiber boards bonded with UF resin, analyzed the differences existed among different layers of straw stalk and discussed the mechanism of manufacturing straw MDFs by different pretreating as well. The following conclusions were drawn based on the research:1. Urea-formaldehyde resin modified with Melamine ( MUF ) was a proper resin to bond rice and wheat straw fiber boards, and was an alternative to MDI resin in this application. The best 1 synthesis parameters of this resin were as follows: Moore ratio of formaldehyde to urea was.3, the pH value of the synthesis was 4.9-5.0, the reaction temperature was 85(?), and the addition amount of the melamine was 5%.2. By analyzing of mechanism of UF and MUF resins which prepared at the same molar ratio, it was found that the degree of glue joining improved with lower contents of methylol end groups and higher resistance to water attack. And DSC showed that MUF resin demanded higher curing temperature compared to UF resin. The surface tension of the MUF resin was 6.3% less than that of UF resin, hence the wetting ability of MUF to straw fiber was improved, which was good for MUF glue to diffuse and penetrate into fiber element and resulted in higher bond strength.3. Though all the straw pretreatments improved performances of straw-based fiberboards, straw pretreated with xylan enzyme was the best in terms of properties of the final boards. The best condition for this pretreatment were reached at a pH value was 4.5, a temperature of 45℃, a mass ratio of 6 to 1( water to straw), a time period of 2h and an enzyme dosage of 20IU·g-1. It was observed that the surface of wheat-straw became rougher and there were lots of pinholes in the cell wall by scanning the enzyme-pretreated straw with electricity microscope (SEM). Furthermore analysis of the fibers showed that among all fibers defibrated from straws pretreated with different methods, fibers refined from xylan enzyme pretreated straw had the longest average fiber length, the largest length-to-width ratio, the highest proportion...