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Recent studies of the dehydrochlorination of PVC in the solid state offer convincing evidence in support of a mechanism that involves initiation at gttg -conformations in isotactic stereosequences generally considered to be normal units. Attempts have been made to verify such a mechanism by direct measurements, using solution 13C NMR, of the changes in tacticity that result from the degradation. In this paper, computer simulations are reported that use Monte Car10 methods to simulate preferential degradation at isotactic sequences of various minimum sequence lengths. The results indicate that at the levels of degradation accessible to experimental verification by solution NMR (c 2%), the predicted changes in triad probabilities are close to the limits of experimental error and are not a sensitive indicator of the mechanism. The simulations also indicate that for the degradation to result in polyene sequence lengths that correspond to experimentally determined values requires that the dehydrochlorination include some atactic and syndiotactic sequences which, in turn, reduces the changes in P,,. On the other hand, there are some indications that more specific indications can be tPresent address: Paprican, 570 St. John's Blvd., 744 RADlOTlS AND BROWNobtained from the changes in the probabilities for pentads and longer sequences, provided that appropriate NMR data can be generated.

We determined the pulping yields for steam-exploded and untreated mixed hardwood chips for kraft pulping processes with and without anthraquinone and/or polysulphide. The pulp yield from steam-exploded chips was 1 -3% lower than from untreated chips under similar conditions. The benefit of kraft pulping with anthraquinone and/or polysulphide was found to be more pronounced for the exploded chips than for the untreated chips.

Global demand for dissolving pulp has been increasing at a remarkable pace over the last few years. A shortage in cotton and the expansion of the textile, hygiene, and health product markets are behind this booming demand. The Canadian pulp and paper industry has entered these markets by converting several paper-grade pulp mills to dissolving pulp producers. In the kraft process, part of the hemicellulose remains with the pulp after cooking and the rest is burnt in the recovery boiler to produce energy. In dissolving pulp mills, most of the hemicellulose must be removed from the wood chips in a pre-hydrolysis stage before pulping. Hemicellulose hydrolysis and its subsequent extraction will affect energy and chemical balances. In addition, the new operation will require large capital expenditures. The objective of this work was to study the conversion of a kraft pulp mill to a dissolving pulp operation and the extraction of hemicelluloses from the process. The effects of hemicellulose extraction on mill energy balance, equipment requirements, and new operating conditions were analyzed. Computer simulations of the process and thermal pinch analysis were used. The existing bottlenecks (digesters, lime kiln, and recovery boiler) to increasing the dissolving pulp production capacity were identified before and after the conversion. In addition, energy efficiency measures were identified to decrease the energy consumption of the new process.