In order to improve the mechanical and physical properties of fiberboard, the graft copolymerization of methyl methacrylate (MMA) onto wood fiber (Lauan Asplund pulp) was investigated, and the effects of the grafting on the dimensional stability and strength properties of the fiberboard prepared from Asplund pulp-MMA graft copolymer were examined.
The results are as follows:
(1) It was found that H2O2-Fe(II) redox initiation system was very effective for the graft copolymerization and MMA was grafted onto the inner part of wood fiber, mainly on carbohydrate in the early stage of the reaction, and on lignin in later. The molecular weight (Mn) of poly (methyl methacrylate) branches of graft copolymer was in the range of 6.5×105∼9.5×105 and somewhat higher than that of homo polymer.
(2) The dimensional change of the fiberboard made from Asplund pulp-MMA graft copolymer in humidity or watersoak tests decreased with increasing degree of grafting, and the thickness swelling of the grafted board (PMMA content: 15.5%) was less than 8% at 40°C and 90% relative humidity, or less than 15% in watersoak for 24 hours. The decrease of dimensional change was considered as resulted from the dimensional stability of each wood fiber much more than the increase of bonding strength between the grafted wood fiber.
(3) The modulus of rupture and the modulus of elasticity of the fiberboard made from Asplund pulp-MMA graft copolymer in bending increased with increasing degree of grafting, but the effect by MMA grafting was not so much as that by urea- or phenol-formaldehyde resin.
