Читайте также:
|
|
extensively described and reviewed in the relevant literature [1–3]. The following
Section on paper-grade pulp is limited to a short description of certain chemical
And macromolecular properties which are rarely presented in the literature. (The
Chemical and macromolecular properties of chemical paper pulps, however, were
Rarely the subjects of published literature. This section is therefore concerned
With a very short description of important differences in chemical and macromolecular
Properties of a selection of chemical paper pulps.)
11.2
Paper-Grade Pulp
Chemical paper-grade pulps can be categorized into hardwood and softwood sulfite
And kraft pulps. The definite differences in pulp properties between sulfite
and kraft pulps have been the subject of numerous studies [4]. Jayme and Korten
Advanced a hypothesis that, for a given degree of delignification, sulfite pulps
were more degraded on the outside of the fiber than were kraft pulps [5]. This
hypothesis was supported by Luce, who developed the method of “chemical pulping”
to study the radial distribution of different properties across the cell wall [6].
According to his results, the molecular weight of the polysaccharides of the kraft
Pulp was uniform throughout the fiber wall, while in the sulfite pulp it was low at
The outermost layers and increased towards the inner layers. The significantly
Pulp Properties and Applications
Lower molecular weight of the residual hemicellulose fraction in sulfite as compared
to kraft pulps has been also pointed out by Jayme and Koppen [7]. It can be
Concluded that (acid) sulfite cooking liquor penetrates through the pits into the
Porous middle lamella where delignification proceeds from the primary wall. The
Degradation reaction involving both lignin and carbohydrates thus proceeds from
The outer to the inner cell wall layers, and this results in a broad molecular weight
Distribution of the polysaccharide fraction. In contrast, alkaline cooking conditions
Promote rather uniform pulping reactions due to the high swelling properties.
Hamilton and Thompson have studied the main differences in the carbohydrate
Constituents of wood celluloses prepared by the sulfite and kraft pulping
processes [8]. According to their findings, xylan from hardwoods is converted to
Low molecular-weight 4-O-methylglucuronoxylan by the acid sulfite pulping procedure,
And to a rather high molecular-weight xylan with a low number of uronic
Дата добавления: 2015-10-21; просмотров: 119 | Нарушение авторских прав
<== предыдущая страница | | | следующая страница ==> |
To applications such as newsprint, toilet tissues, and paperboard as they tend to | | | Acid side chains. The glycosidic bond between uronic acid and the xylan backbone |