Environmentally-friendly paper production
Until now chemical pulping practice has been based primarily on the Kraft process, which generates a significant amount of sulphur emissions. In order to rid the paper industry of this age-old stench, the European Commission funded a consortium of ten organisations to develop and optimise sulphur-free pulping procedures. Unfortunately, removing sulphur from the process negatively affects the ability of the pulp to be bleached. The School of Paper Science and Graphic Industries of the National Polytechnic Institute of Grenoble (EFPG/INPG) aimed to resolve this problem for both softwood and hardwood pulps produced with the sulphur-free Novacell process developed in Sweden. With respect to softwoods, the French scientists determined that the introduction of ozone or hydrogen peroxide into the process significantly improved brightness. The key was to maintain the degree of delignification, denoted by the kappa number, as low as possible following cooking. It was also noted that total yield increased when ozone was incorporated. Ozone also proved to be successful in the case of hardwood pulps. The reason ozone is so effective is that it removes hexeneuronic acids that otherwise discolor the subsequent paper products. An alternative method was also identified that calls for increasing the amount of chlorine dioxide used, but this is less environmentally friendly. Recommendations for the specific sequence of chemical stages in the pulping process are available from EFPG/INPG.
