Performance assessment of deashed and dewaxed rice straw on improving the quality of RS-based composites

In order to obtain high performance rice-straw-based composites, the synergistic effect of deashing or dewaxing on the bonding behavior of rice straw (RS) fibers by eco-urea formaldehyde (UF) adhesive was assessed. The deashing and dewaxing were performed by mechanical, alkali, physical and biological treatments. The eco-UF adhesive was provided by a commercial formaldehyde-scavenger system. The chemical constituents of untreated and treated RS were estimated by Fourier transform infrared spectroscopy (FTIR) and non-isothermal thermogravimetric (TGA) analyses. The benefit of these treatments was evaluated by comparing the strength and water resistance properties of the produced agro-composites with those obtained from untreated RS bonded with UF-free scavenger, or by polymeric diphenylmethane diisocyanate (pMDI). The data showed that the extent of increased mean hydrogen bond strength (MHBS) was in good agreement with the efficiency of removing the silica rather than the wax. It is interesting to note that the modulus of rupture (MOR), and internal bond strength (IB) of board produced from relatively highly deashed and dewaxed RS (via mechanical followed by alkali treatment; RS-MT-AT fibers) and UF-containing scavenger are nearly the same as those values for board produced from traditional pMDI resin bonded RS (similar to 16.9 MPa, and 0.32 MPa, respectively). However, the thickness swelling (TS) of the investigated board is higher (17.4%) than the traditional ones (similar to 12%). It can be seen that the biological treatment approach (RS-BT) provided more highly dewaxed fibers and higher water resistance properties (similar to 13%). Among the board types tested, the MOR and IB properties of RS-MT-AT and RS-BT boards met the ANSI standard A208.1-2009 requirements for wood particleboard of class M-2. RS fibers produced from physical treatment (RS-PT), resulted in board meeting the requirements of MOR and IB of class M-S.