APMP pulps from nonwood fiber part 2: Jute.

Application: Laboratory results suggest that jute pulp is suitable for use in printing/writing, tissue, and paperboard grades.

Interest in the use of nonwood fibers continues to grow, especially in countries where wood resources are limited. Nearly all of the mills that process nonwood fibers rely on some type of chemical pulping process. Refiner mechanical pulping has been a much less popular alternative, mainly because of concerns about excessive fiber shortening and insufficient pulp strength development. However, recent advances in pulping technology have prompted a shift toward combined chemical-mechanical treatments, including APMP (alkaline peroxide mechanical pulping), CTMP (chemithermomechanical pulping with alkaline sulfite), CCS (cold caustic soda mechanical pulping), and the latest innovation, a preconditioned APMP followed by refiner chemical treatment (P-RC APMP).

Study objective

This is the second in a series of papers exploring the potential of applying chemical-mechanical pulping processes on nonwood fibers. The first paper investigated APMP pulps from kenaf and straw. This second paper presents results from APMP pulping of whole jute (bark and core) from India. Jute pulp properties are compared with aspen APMP and market BCTMP (bleached chemithermomechanical pulp) pulps. Since both APMP and BCTMP aspen pulps are currently used in many value-added paper grades (printing/writing, tissue, and paperboard), the results of this study provide a benchmark for evaluating the utility of jute APMP pulps.

APMP process

The APMP process was chosen because previous research has demonstrated that it is more efficient than other chemical-mechanical pulping processes (CTMP or CCS). Moreover, nonwood fibers are more amenable to treatment with alkaline chemicals than hardwoods.

Pulps from whole jute were produced under various chemical charges (2.9%-3.5% total alkali, 2.5%-2.9% [H.sub.2][O.sub.2]) and different levels of refining energy (630-1600 kW*h/ ovendry metric ton). Whole jute (15% moisture) was hammermilled through a screen with 1-in. holes, soaked in water, and then pressed. Chemical liquors were applied at the discharge of the press, and the material was retained for 20 minutes without steaming before being refined in two stages. By varying the chemicals and the refining energy, it was possible to investigate the development of intrinsic pulp properties, especially strength.

Strength properties

Given the importance of handsheet density, or bulk, in papermaking applications, this study focused on the correlation between pulp strength properties and handsheet density rather than absolute values of the strength properties. Figure 1 shows the tensile strength development of jute and aspen APMP pulps. At a given density, jute APMP had a higher tensile index, by about 10 N*m/g, than aspen APMR Under the applied chemical and energy conditions, the jute APMP achieved a tensile index of about 60 N*m/g (a breaking length of more than 6 km), which is stronger than most hardwood market BCTMP pulps. Jute also outperformed aspen in other strength properties such as burst, stretch, and tensile energy absorption (TEA).

[FIGURE 1 OMITTED]

Optical properties

Despite its initial dark color, the whole jute was relatively easy to bleach in the APMP process. A brightness of 70% ISO was achieved using 2.5% [H.sub.2][O.sub.2] and without any post-bleaching. The jute APMP pulps also had a very high light scattering index compared with the aspen pulps.

Conclusion

Jute APMP had greater strength at a given level of bulk and better light scattering than aspen APME suggesting its potential application in printing/writing, tissue, and paperboard grades.

Xu is a process and R&D scientist at Andritz, Inc.'s R&D Lab, 3200 Upper Valley Pike, Springfield, OH 45504, USA. Address correspondence to Xu by email at [e-mail].