Unwanted halogen substances in paper: MARE’s approach

Compliance with regulatory requirements is now an everyday activity for paper manufacturers. In particular, the presence of 1,3-dichloro-2-propanol (DCP) and 3-monopropane-1,2-diol (mCPD) is controlled in tissue paper products, in the manufacture of which polyamidoaminoepichloride resins are known to be widely used for the development of wet strength (WSR). DCPs and mCPDs are part of a larger family of undesirable substances, referred to by the generic term AOX/OX. The final level of AOX/OX found within a roll of kitchen paper on the supermarket shelf is not only a function of WSR application factors, but originates in several factors. Defining the various contributions to the final AOX/OX content of a tissue product requires a systematic investigation of the production chain (mixture preparation/wet part/dry part/converting). Conducting comprehensive studies of this kind requires demanding technological resources and close collaboration between WSR and paper manufacturers.

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MARE has all the analytical tools and expertise needed to conduct this type of investigation and to define potential sources and quantify their contribution. MARE works on this type of study with an integrated approach that starts with thorough research at the synthetic and analytical levels and generates continuous improvements at both the production and application levels.
One of the best known, and best understood by the market, consequences is the obtaining of gradually more efficient and “cleaner” WSR products thanks to the continuous upgrading of technology and production and purification facilities. In this context, the collaboration between our research group and the Politecnico of Milan is fundamental in the projects dedicated to the study of the kinetics of epichloride side reactions, exemplified in Fig. 1. Application expertise is equally essential in this context. In fact, the characteristics of the fiber used are the starting point for the design and application of a WSR product, as well as the first object of study to define the AOX/OX contribution determined by the mixture itself.

A well-defined use of, for example, carboxymethyl cellulose (CMC) generates an important synergy with WSR, allowing a significant increase in wet strength development. This can result in optimization of WSR dosage and, consequently, better control of residual AOX/OX and application costs. In particularly fortunate cases, the use of our CMC-based products has resulted in WSR dosage reductions of up to 40 percent. Continuous monitoring of the papermaking process plays a key role in achieving and maintaining these results. Uncontrolled variation in a number of cycle chemistry parameters (pH, conductivity, cationic demand, zeta potential, etc.) can adversely affect WSR performance and the final level of contaminants on the paper. It should be noted, for completeness of information, that treatments other than WSR-based treatments can potentially generate AOX/OX on the paper (freshwater treatment, charge control, Yankee coating, to name a few) in even larger quantities than those produced by the resin.

Semi-finished tissue is finally subjected to mechanical and thermal treatments, such as embossing, to be transformed into well-known consumer goods such as a packet of tissues or a roll of kitchen paper, which require further handling, such as packaging and transportation, after which the finished product ends up on the supermarket shelf. Only a comprehensive investigation of the entire production chain allows us to collect a coherent data set, composed of relevant data, from which we can draw valid conclusions about the origin of pollutants on paper and decide on effective actions for their moderation. We sincerely hope that we have succeeded in these few lines in describing MARE’s approach to the management of AOX/OX on paper. Only a close cooperation between the paper manufacturer and the chemical additive supplier can enable definitive and decisive results to be achieved.