Laboratory assessment of the potential of Nigerian-grown Gmelina Arborea Roxb. for newsprint manufacture

Extension of pulp and paper raw material base by increased utilization of hardwood species is one reasonable approach to the solution of the world fiber shortage problem. This is particularly so if mechanical pulp with adequate mechanical and optical properties can be produced from fast-growing hardwoods which have not been used to any great extent in the past as a raw material. Laboratory studies reported in this thesis were carried out to assess the response of Gmelina arborea Roxb., a hardwood grown extensively in Nigeria, to mechanical pulping. In this work, both open discharge and simulated thermo-mechanical refiner groundwood pulps were produced. In the latter case, the effect of chemical pretreatment with both sodium sulfite and sodium hydroxide was also evaluated. It was found that while open discharge and standard thermo-mechanical treatments resulted in mechanical pulp with inferior properties, the treatment of chips of Gmelina arborea Roxb. with a 1% sodium hydroxide solution at 250DF (121°C) for 10 minutes prior to open discharge refining resulted in a mechanical pulp having mechanical and optical properties comparable to and, in certain aspects, better than those of stone groundwood used in North American newsprint. The behaviour of this chemically pretreated refiner pulp from Gmelina in admixture with softwood kraft was also investigated. It was found that the properties of newsprint furnish handsheets containing mixtures of Gmelina mechanical pulp and West Coast semi-bleached kraft (SBK) compared favourably with those of handsheets produced from typical West Coast newsprint furnishes, thus indicating the possibility of using chemically pretreated Gmelina thermomechanical pulp (TMP) with reduced amounts of softwood SBK. To cover the situation for a fully integrated mill, a brief study was included to assess the response of Gmelina to kraft cooking, and to evaluate the behaviour of this pulp in admixture with Gmelina mechanical pulp. As expected, the kraft pulp from Gmelina was significantly weaker, mechanically, than North American kraft pulps and its deficiencies were clearly evident in the properties of mixed furnish handsheets. It was concluded, from this part of the study, that newsprint containing both its chemical and its mechanical pulp components from Gmelina would require excessively large proportions of Gmelina chemical pulp and still exert a limiting influence on paper machine speed and subsequent printing operations because of its strength deficiencies.Forestry, Faculty ofGraduat