Pulps, never-dried

Cellulose is a partly crystalline and highly hydrogen-bonded substrate. Consequently it is much less accessible to grafting than starch (2). The present paper describes grafting experiments with the Mn -initiator applied to never-dried pulp fibers from wood and to fibers from cellulose derivatives of low degrees of substitution, i.e. cellulosic substrates known to be more accessible to chemical reactions than other cellulose fibers after drying. 

Dried and never-dried pulps have the same lignin, hemicellulose, and cellulose content at the same yield, but very different digestibilities. The composition of a pulp is therefore a poor guide to its digestibility, some other factor obviously being of considerable importance, and, if this is true of the present series of samples, it is likely to be true also of forages of different species or maturity. 

The extent of swelling of the samples will now be considered. As described in the Experimental section, the solute exclusion technique provides a simple and unambiguous measurement of the amount of water contained within the cell wall and in Figure 7 this quantity is plotted against the yield of pulp. Two features of these curves are worthy of note one is that the never-dried pulps are more swollen than the pulps which have been dried and reswollen, and this is in accord with the different digestibilities of the two sets of samples, substantiating the... 

J. Stone Yes, at the same pore size the dried and reswollen pulp had a lower lignin content than the never-dried pulp. It also had a higher digestibility. We feel that this is due to the difference in composition of the material lining the pores. Thus, digestibility is likely to be a simple function of pore size only for substrates of the same composition. ... 

J. Stone Yes, the lignin content is important, but as I think I pointed out, if you take a never-dried pulp and dry it then it has exactly the same lignin content, but very different digestibility. So there are a number of factors bearing on the system. ... 

This mild hydrolysis retained the high aspect ratio of the fibrils, giving a highly entangled gel-network in aqueous suspension. Another method was presented by Saito and coworkers [33], who used TEMPO-mediated oxidation (Section 8.5.4.1) of never-dried pulp before homogenization. This treatment rendered the microfibril... 

Figure 5.8 2H NMR quadrupole splittings for D20 adsorbed on to never dried bleached Kraft softwood pulp refined to different degrees (25000 and 500 revolutions in a PFI mill).

Our experimental work started from the following original cellulose samples (a) acetate-grade, bleached cotton linters, DP 1800 (b) hot, refined, spruce, sulphite-dissolving pulp, machine dried, ca. 93% a-cellulose, DP — 750 (c) never-dried, normal, rayon-grade, beech sulphite pulp, ca. 90% a-cellulose, DP = 825 (d) commercial cellulose powders obtained by hydrolytic degradation and/or mechanical disintegration of cotton linters or spruce sulphite pulp. 

In agreement with this hypothesis is the remarkable low rate constant with a never-dried beech sulphite dissolving pulp compared with the dried sample at identical conditions of aqueous acid hydrolysis (Table VI). 

Grafting of dissolving pulp (MDC) and grease-proof pulp (GP) (both are bleached sulfite pulps from spruce) and low-substituted ethyl cellulose (EC) and hydroxyethyl cellulose (HEC), all samples in never-dried state, with acrylonitrile (AN) using Mn +ions, complexed with pyrophosphate ip n inin amr >s... 

The effect of fines was studied for unbleached, never-dried spruce sulfite pulp (yield 57.6%). The fines were removed using a 200-mesh screen. The non-freezing water was measured for the pulp and the rewetted handsheets. To prepare a sheet from fines, the fines suspension was poured Into a flat dish and the water allowed to evaporate under ambient conditions. The sheet did not disintegrate on rewetting. 

Table II Non-freezing water for fines, flnes-free pulp and hand-sheets, the never-dried sulfite pulp beaten in valley beater.

Figure 3. Effect oj beating on never-dried Kraft pulp ( ) pulp (0) rewetted...

In contrast, no new small pores are created on beating a never-dried softwood pulp and thus the non-freezing water shows no change. 

The crystallinity of the cellulose is often quoted as a factor of considerable importance in digestibility but it obviously has little bearing on the susceptibility to attack of the present samples because the crystallinity of cellulose certainly does not decrease as a result of pulping if anything, it increases. Similarly, never-dried and dried and reswollen pulps have very similar crystallinities but very different digestibilities. 

Figure 7. Fiber saturation points of the pulps in the dried and never-dried states...

J. Stone I think there is no difference in the pore size distribution. For a given pore size the dried material is more digestible than the never-dried material, but it is also a lower yield pulp—i.e.y it has less lignin. A possibility, therefore, is that in drying the sample the pores which remain open are more cellulosic. One has to bear in mind not only the size of the pores, but the nature of the surface of the pores. This matter is also involved in the question as to why the enzymatic reaction with cotton slows up after an initial rapid rate reaction. Again, I think we are getting into the question of the nature of the surface of the pores. ... 

In this investigation, two types of equipment are considered for refining together never dried bleached Kraft pulp, composed of pine and spruce, and milk of lime. They are as follows ... 

Chemical treatment Never-dried bleached-sulfite/kraft pulp TEMPO-mediated oxidation, followed by disintegration in a Waring blender Few nm in width... 

Activation of Cellulose. The activation required depends on the source of cellulose (cotton linter or wood pulp), purity, and drying history. Typical specifications for an acetylation-grade cellulose are given in Table 5. Cellulose that has never been dried or has been mildly dried to ca 5% moisture requires Htde, if any, further activation. 

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