Fibre lignin content

The fibre lignin content is a central issue since high lignin contents tend to impact negatively on strength development in paper and paper wettability, as well as on the long-term stability of paper. Figure 7.2 shows... 

From the bark of the hemp stems, bast is obtained. The bast fibres are separated mechanically from the woody parts modern separation methods employ enzymes or steam pressure, surfactant or ultrasound processes. The best hemp fibres are obtained from the male plants being very durable. They are used for the manufacture of ropes, cords, nets, strings, yarn, carpets, textiles and sailcloth. The wood is used for the manufacture of insulating material, but it is also well suited for the production of paper, cardboard and cartons, since its lignin content amounts to only 10% (compared to 20-25% from trees). 

Figure 7.2. Effects of different bleaching sequences on the fibre surface content of lignin TCF, total chlorine free ECF, elemental chlorine free. The bleaching steps are oxygen delignification (O), ozone (Z), peroxide (P), chlorine dioxide (D) and alkali extraction (E). (From ref. (4) with permission)...

Isora is found to be a cellulosic rich fibre with comparatively less lignin content. 

In terms of crystallization and thermal behaviour, no significant effect of cellulose on PHB crystallinity was reported. A slight increase of Tg and a delay in the crystallization process were observed. The presence of cellulose fibres also increases the rate of PHBV crystallization, due to a nucleating effect, while thermal parameters, such as crystallinity content, remained unchanged. Studies on the crystallization behaviour of PHB/kenaf fibre biocomposites showed that the nucleation by kenaf fibres affected the crystallization kinetics of the PHB matrix. Differences in the effect of cellulose fibres on the crystallization process have been attributed to the lignin content at the surface/interface of the cellulose fibre. 

Wheat bran cellulose is much less well digested than that of fruit and vegetables and this has been attributed to its lignin content. The chief products of the anaerobic fermentation of fibre are volatile fatty acids (acetate, propionate and butyrate), gas (CO2, Ha and methane) and energy. Gas production is a normal part of colonic metabolism but may be one of the reasons why people in the West have tended to maintain a relatively low fibre intake. 

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