| Résumé : |
The efficient control of contaminants such as metals, plastics, inks and adhesives during the processing of recovered paper products determines the profitability of recycling mills. In fact, it is arguably the most important technical obstacle in expanding the use of recycled paper.1-4 An especially challenging category of contaminants to manage is pressure-sensitive adhesive (PSA). PSAs are soft elastomer-based materials that are highly viscous and sticky to the touch. In recovered paper, they are usually found as part of pressure-sensitive (PS) label systems, consisting of facestock coated with a 0.7-1.0 mil layer of PSA.
During the initial stages of the paper recycling process, the bonds between fibers are broken using water and mechanical energy. This operation, known as repulping, also fragments adhesive films. Much of the removal of these fragments in the recycling process occurs at the pressure screens and is governed mainly by the size and shape of the residual adhesive. The PSA that is not removed by screening is introduced into the remaining fiber recovery operations and the papermaking process, where it can significantly diminish production efficiency and product quality.
A widely acknowledged approach to reduce the negative impact of PSA on paper recycling is to design adhesives for enhanced removal early in the recycling process. Given the high efficiency of particle removal demonstrated by screening operations, the most promising PSAs are those designed to generate larger residual particles.
Our recent research efforts have focused on developing guidelines for producing these types of PS products. This article includes the rationale for our test methods to gauge screening removal efficiencies, the identification of properties controlling the fragmentation of both hot-melt and water-based PSAs, and a discussion of the role additives and laminate design play in determining the fragmentation behavior of adhesive films. |
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Recycling pressure-sensitive products in ADHESIVES & SEALANTS INDUSTRY (ASI), Vol. 19, N° 4 (04/2012)
