Improving recyclability of double-side silicone coated release liners to make Pressure-Sensitive Adhesive (PSA) tapes more sustainable and circular

Two-side silicone-coated supercalendered paper (glassine) release liners are a key component of double-sided Pressure-Sensitive Adhesive (PSA) tapes for many industrial and consumer applications. Common belief is that these liners are not recyclable with paper., but Ahlstrom’s recent advances challenge the status quo. 

Silicone-coated paper release liners serve as a critical component in double-sided adhesive tapes. Their primary role is to protect and carry pressure-sensitive adhesives until application.  The silicone layer provides a smooth, non-stick surface that ensures easy release without damaging the adhesive, maintaining its performance and integrity for various applications. 

Recycling of silicone coated paper liners 

With the target of increasing sustainability and circularity, recyclability of silicone coated release liner is one of the key priorities of the industry consortium CELAB Europe (Circularity for Labels - celab-europe.org) and of the industry association IRLA (International Release Liner Association - irla.info ). These initiatives have already identified several effective recycling options for silicone coated paper liners, whether silicone coated on one side, used to carry PSA labels, or silicone-coated on both sides, as-used in double-sided PSA tapes. 

When liners are recycled through repulping, the goal is to recover fibers and reuse them in new paper or cardboard products. This process involves disintegration in water, separation of silicone and other contaminants, and reintegration of clean fibers into conventional paper streams. This procedure prioritizes fiber quality and compatibility with existing paper grades. 

In contrast, alternative recycling pathways also exist. For instance, the conversion of the liners into cellulose-based insulation materials, is less sensitive to fiber length or residual silicone. This application can tolerate minor impurities because the fibers will form insulation flakes or mats rather than high-quality paper sheets. Such flexibility allows for broader acceptance of materials like two-side silicone coated liners or darker colors, which are on the other hand harder to repulp efficiently into new paper. 

How to measure recyclability 

In this framework, the Recyclability Laboratory Test Method published by CEPI (Confederation of European Paper Industries), is the standard of reference to assess recyclability through repulping.  

The Test Method is divided into three parts, defining Harmonized European laboratory test method to generate parameters enabling the assessment of the recyclability of paper and board products in three different scenarios, depending on equipment available in the paper mill: 

In particular, the laboratory procedure described in Part I emulates the most relevant phases (pulping, screening, sheet formation and visual impurities) of recycling mills equipped with conventional process, (without flotation-deinking technology or other special features), say the most challenging among the three scenarios. This is also the methodology chosen by Ahlstrom for its internal assessment of recyclability of paper products. 

Many Ahlstrom paper products are tested every year at our corporate research center in France, a crucial hub for Ahlstrom sustainable innovation, integrating technology research, product development, and industrial expertise for the group.  

According to CEPI test, results are expressed with a number from -100 to +100, where values below 0 represent a non-recyclable product, while values above 0 signify a recyclable product. 

Prior to silicone coating, glassine release base papers are rated as fully recyclable, achieving a very positive score according to CEPI method part I V.3. 

One-side silicone coated glassine liners are also rated recyclable in standard paper recycling conditions. CEPI test protocols confirm that fibers can be recovered without negatively impacting mixed paper streams, and the recovered fibers can find new life in recycled containerboard, pulp or paper products. 

While one-side coated liners allow water penetration and easier fiber release, two-side coated glassine liners pose greater challenges. Since both surfaces are hydrophobic, water absorption is reduced and disintegration is slower. In addition, the percentage of reject material is higher during the screening process, partially also because of the higher amount of silicone. These factors are the cause of negative scores obtained by two-side coated liners, which are rated Not Recyclable when tested according to CEPI methodology. 

Latest advances towards more sustainable and circular liners 

This is one of the limits that Ahlstrom wanted to challenge when applying the concept of Safe and Sustainable by Design (SSbD) to the development of better release liners for PSA tapes.  

Ahlstrom’s SSbD concept is aligned with the European Commission’s framework for safe and sustainable design for chemicals and materials and is based on several environmental and product-related criteria. 

Driven by this methodology, Ahlstrom have recently introduced to the market its Acti-V® RF Natural release liner papers for double-sided PSA tapes. Designed for silicone coating on both sides, these contain a mix of unbleached cellulose fibers and post-consumer recycled fibers, and do not include any dyes. Their low-impact raw-material composition allows a reduction of carbon footprint up to 20% compared to standard ActiV® Industrial Brown liners*.  

Following to that, our release liner team worked further to also increase end-of life recyclability of double side silicone coated glassine liners, leading to the development of Acti-V® RRF Natural products. Thanks to the unique RRF re-pulpable formulation, still based on recycled and unbleached fibers, these new glassine products remain recyclable with paper4 even when double side siliconized, marking a truly remarkable advance versus conventional supercalendered release liners for PSA tapes. 

The possibility to safely use a lighter paper can grant a significant further saving in carbon footprint per unit of product.  For example, the -20% lower CFP per Ton of product* is equivalent to -25% lower CFP per m2, when considering the reduction of 6 g/m2 compared to standard ActiV® Industrial Brown 78g. 

Addressing the full life cycle of the product, from raw materials to end-of life, and combining benefits in terms of carbon footprint, recycled content, and unique recyclability of the silicone coated liner, the new Acti-V® RRF Natural provides a truly innovative solution to environmentally conscious double side PSA tape producers and users.

Article by:   Alice Bongioanni Research & Development Specialist, Release Liners