Challenges with Mechanical Recycling of Multilayer Packaging Plastics
The widespread use of multi-material multilayer plastic (MLP) packaging in fast-moving consumer goods has become a common phenomenon, placing emphasis on leveraging the unique functionalities of various materials. These packaging structures offer advantages such as improved resource-use efficiency and enhanced barrier performance, contributing to extended shelf-life and other consequential benefits. However, despite their utility, MLPs pose a formidable challenge to existing recycling systems, presenting significant hurdles to the principles of a circular economy. The intricate composition and complex nature of MLPs raise concerns regarding effective recycling, necessitating a closer examination of the associated challenges and potential solutions to enable their alignment with sustainable practices.
Multi-layer plastic recycling presents a series of formidable challenges due to the intricate nature of its composition. These plastics often incorporate a blend of diverse polymers like PE and PP along with the tie(adhesive) layers, resulting in a complex structure that hinders effective separation and recycling. The distinct melting points and chemical compositions of the various layers pose compatibility issues during the recycling process, making it difficult to achieve uniform reprocessing. Additionally, the presence of barrier coatings designed for specific properties, such as protection against moisture and oxygen, proves challenging to remove, impacting the quality of the recycled material. The absence of standardization in MLP, combined with the use of different layering techniques by manufacturers, further complicates the establishment of a universal recycling process. Collection and sorting difficulties arise from the prevalent use of these plastics in flexible packaging, like pouches and sachets, which are both lightweight and small, hindering efficient recycling facility operations. The recycling of MLPs can be costlier than producing new materials, and thus economic viability becomes a significant concern. Moreover, limited market demand and potential contamination with food residues or adhesives create additional obstacles. Technological advancements are crucial to developing effective methods for separation, cleaning, and recycling, while environmental considerations regarding energy consumption and emissions during the recycling process add another layer of complexity.
The Design for Recycling concept is one such aid to address some of these issues. The plastic packaging recycling system involves various standards for individual plastics and specific applications, such as flexible packaging. Let us look at the popular example of "PET Products Recyclability Design Guidance," where the focus is on achieving bottle-to-bottle recycling of PET. Key design elements impacting recyclability include base resin, barrier layer/coating/additives, labels/inks/adhesive, closures, color and dimensions, and attachments. Preferred designs include PET copolymer resins, bio-based PET resins, and recycled PET, while additives like PVDC may hinder recycling. Labels and inks play a crucial role, requiring thorough removal of adhesives for accurate PET bottle sorting. Density considerations guide the choice of materials for closures, and color choices influence cost-effectiveness and contamination risks. Attachments made of PET or easily separated materials are preferred, with caution against problematic materials like PVC and PLA. The overall goal is to optimize design for efficient and high-value PET recycling.
Designing recyclable plastic packaging involves addressing the core functions of packaging—protecting products, ensuring convenience, and promoting sales. This design process primarily encompasses material design, structural design, and decoration design. In material design, the challenge of recycling multilayer packaging is addressed through innovations such as Colgate's recyclable toothpaste tube, which replaced traditional LDPE-aluminum combinations with easily recyclable HDPE.
Additionally, bio-based and biodegradable materials like PLA and PHAs can be explored as substitutes for conventional plastics. Structural design innovations, crucial for recyclability, include the development of all-plastic pumps by Tianzhou Packaging and Coca-Cola's introduction of plastic bottles with attached caps which are recyclable. These advancements simplify disassembly and promote recycling enthusiasm. Decoration design focuses on balancing aesthetics with recyclability, urging brands to minimize excess inks, pigments, and oversized labels. Some brands opt for label reduction or removal, while others employ techniques like embossing, laser printing, and electronic tagging to convey essential information without hindering recyclability. The trend towards transparent and light-coloured bottles further supports recyclable packaging efforts.
Picture Credits: https://meyers.com/meyers-blog/sustainable-brand-packaging-statistics-why-eco-friendly-packaging-matters/
Another perspective on the issue of single-use plastics could be framed around the concept of "behavioral design for sustainability." This school of thought emphasizes the importance of understanding and influencing human behavior in order to address the environmental impact of single-use plastics. In this view, the argument is that, simply banning or restricting the use of single-use plastics may not be sufficient, as it fails to account for the complex and varied behaviours of individuals once the packaging leaves the point of purchase. Instead, proponents of this perspective advocate for a proactive approach that incorporates principles from behavioural psychology into the design of packaging. By understanding how people interact with and dispose of packaging, designers can create solutions that align with human behavior, making it more likely that individuals will choose sustainable options. For example, packaging could be designed to be easily recyclable, with clear and simple instructions on how to do so. Alternatively, it could incorporate incentives, such as deposit systems, to encourage proper disposal and recycling. This approach recognizes the inherent unpredictability of human behavior and seeks to leverage that understanding to foster environmentally conscious choices. Ultimately, the idea is that by aligning design with human behavior, we can create more effective and sustainable solutions to reduce the impact of single-use plastics on the environment.
The widespread use of MLPs in fast-moving consumer goods offers valuable benefits but presents formidable challenges to recycling systems. The intricate composition of MLPs, incorporating diverse polymers with distinct melting points and barrier coatings, hinders effective separation and recycling. Lack of standardization, collection difficulties, economic concerns, and technological limitations compound these challenges. The Design for Recycling concept, emphasizing material, structural, and decoration design, emerges as a crucial aid. Innovations such as Colgate's recyclable toothpaste tube demonstrates the potential of sustainable design. To address the multifaceted issues surrounding MLP recycling, a comprehensive approach, which incorporates the integration of technological advancements, sustainable design practices, and an understanding of human behavior, is imperative for fostering a more sustainable and circular approach to plastic packaging.
If you have any other questions or would like to suggest topics for us to write about, please feel free to contact us at prashant.gupta@polymerupdateacademy.com
Author
Dr. Prashant Gupta
Faculty, Polymerupdate Academy
