Effects of hot water and alkali pretreatment on yield and optical and resistance properties of Beech CMP pulp

Some extractive compounds from wood, adhesives which are difficult to remove during pulp washing and cause adhesive residues on process equipment. In preparing pulp from hardwoods, These compounds are the source of numerous problems such as the formation of sticky materials, impurities remain in the paper pulp and paper break in paper machine. In addition, remain these compounds on paper caused problems such as creation dark spots and paper fibers stick on the cylinder surface, paper breaks and clogging with and felt. Also the extractives may react with chemical bleaching and produce changed and oxidized products. Changed extractives are causing pitch problem and have a negative impact on pulp brightness. In this study, the effect of hot water and alkali pretreatment on bleach ability of hornbeam CMP pulp was studied.

Methods and materials:
Hornbeam wood chips prepared from Mazandaran wood and paper mill. Treated with hot water and alkali done in three levels of 0.5, 2 and 3.5 percent with the aim of removing the extractives before pulping process and then prepared pulp from control and pre-treated wood chips with the same conditions and CMP process and bleached with hydrogen peroxide. Handmade paper produced from the resulting pulp and papers optical properties before and after bleaching and strength properties of produced papers before bleaching was examined.


Results:
The sample pre-treated with stable temperature and time, the mass loss during pretreated with hot water is less than pre-treated with alkali and in the alkali treatment, the mass loss increased with increasing alkali percent. In both pretreated cases, pre treated hornbeam chips pulp yield is more than control sample. The refining rounds and energy consumption of paper pulp produced from alkali pretreated chips is more than pulp from wood chips pre-treated with hot water. The brightness of hot water and alkali pre-treated samples before and after bleaching Increased compared to the control sample. During alkali pre-treated, with increasing the percentage of alkaline, pre-treated samples also showed an increase brightness. Before bleaching, opacity of sample pre-treated with hot water had low increase and in general, significant differences between the samples treated with hot water and control at the level of 5% was no observed. The sample pre-treated with stable temperature and time, the hornbeam tensile index increased. Pretreatment with alkali also increases the tensile index. Burst index increased by hot water pretreatment. Pre-treated with alkali also increase burst index. Samples pre-treated with hot water and alkali showed that tear index increased and rised with the alkaline percentage increase.

Conclusion:
Hornbeam wood chips pre-treated with hot water and alkali caused wood chips mass reduce and increase CMP wood pulp yield compared to the control. Brightness of pretreatment samples before and after bleaching increased than the control sample. Opacity in the samples pretreated with hot water increased and decreased during the treatment with alkaline solution. In those pre-treated with hot water and alkaline solution than the control sample, hornbeam paper pulp tear index increased but in burst index and tear strength was no difference significant.