How can upcycled resins help advance the circular economy?

Sustainable materials are receiving greater attention from customers across all healthcare segments. This article, by Vandita Pai-Paranjape, staff scientist, SABIC’s Specialties business and Yuanqing (Emily) He, senior business manager, LNPTM Products, SABIC’s Specialties business, looks at initiatives that SABIC’s Specialties business is pursuing to address industry demand for environmentally responsible material solutions.

The plastic paradox

On one hand, plastics support innovation in healthcare and can help improve medical treatment and patient outcomes. On the other, these materials receive criticism due to their contribution to the growing issue of plastic waste, which is impacting the environment. According to the United Nations Environmental Programme report, “From Pollution to Solution,” the COVID-19 pandemic has exacerbated the plastic waste issue as personal protective equipment (PPE) and packaging are discarded into the environment.

Globally, approximately 400 million tons of plastic waste are produced each year, but plastic is being recycled at an even lower rate than previously estimated. In addition, production, processing and incineration of plastics generate carbon dioxide (CO2) that contributes to climate change. 

Chemical upcycling of plastic waste

To solve this paradox, polymer technology can be applied in two ways: capturing and creating value from plastic waste to reduce its environmental impact and continuing to drive innovation in the healthcare industry with new sustainable polymer solutions. 

One solution to these two imperatives is chemically upcycled polybutylene terephthalate (PBT) resin that is synthesised from discarded single-use polyethylene terephthalate (PET) bottles. Upcycling this post-consumer plastic waste into a material widely used in medical devices can reduce consumption of fossil-based feedstocks and lower CO2 emissions. Further, PBT can be used for more-durable applications than PET, such as medical device and equipment housings. In this way, upcycling can extend the useful life of PET beyond its original application in disposable bottles. 

Drawbacks of PBT reformulation

Polybutylene terephthalate, an engineering plastic offering excellent chemical resistance, strength, stiffness and dimensional stability, is widely used in healthcare applications. It is made from 1,4-butanediol and either terephthalic acid or dimethyl terephthalate building blocks. These monomers are derived from crude oil via several intermediate steps. Purification at each step results in a well-defined product. 

Efforts to replace the diol monomer and the diacid monomer with more-sustainable alternatives, such as bio-sourced components, typically lead to changes in processing and crystallisation behaviour and material performance. Even small structural changes to either monomer can have large effects. The resulting polymers typically cannot serve as drop-in replacements in existing applications. 

Performance changes can also occur when mechanically recycled plastics are mixed with new material. Variation in the composition of most mechanically recycled plastics from post-consumer sources, as well as traces of colourants, stabilisers and other additives, can affect biocompatibility.  

Upcycling PET to higher-value PBT

SABIC’s Specialties business is taking a different approach to enhancing the sustainability of PBT. Using its chemical upcycling technology, the company produces PBT from post-consumer PET bottles—thereby converting commodity plastic into higher-value engineering resin. 

Rather than incorporating molten, recycled PET, SABIC uses PET as a feedstock in a chemical process that deconstructs the material down to its basic building blocks. These building blocks are purified with similar rigour as chemicals coming from a fossil source before being fed into the polymerisation process to prepare PBT resin. SABIC’s process uses dissolved monomers and oligomers from PET and adds fossil-based 1,4-butanediol to produce LNP ELCRIN iQ resin (PBT). Approximately 88 PET bottles (0.5 litre) go into each kilogram of the PBT resin.  

Comparing PBT sustainability

SABIC recently completed a Life Cycle Assessment (LCA) comparing virgin PBT and LNP ELCRIN iQ resin, which underwent third-party critical review in accordance with ISO 14040/14044 standards. The results indicated LNP ELCRIN iQ resin lowered global warming impact by 29% and cut cumulative energy demand by 43% compared to virgin PBT (Fig. 1). 

Delivering key material properties to healthcare applications

Sustainability benefits present a strong argument for replacing fossil-based PBT with LNP ELCRIN iQ resin in healthcare applications. However, other properties of the upcycled PBT resin must be considered to meet application requirements.  

When considering replacement of conventional PBT with LNP ELCRIN iQ resin, customers can consult technical datasheets. As shown in Table 1, the properties of the upcycled PBT material are similar to those of a standard, unfilled PBT of comparable viscosity. Specifically, the table compares key properties of LNP ELCRIN W1000JiQ resin with those of SABIC’s VALOX HX260HPR resin, a fossil-based PBT grade. This comparison reveals strong similarities between the two materials. Even a parameter like mould shrinkage, which is sensitive to small material differences, was identical (1.2%) in a side-by-side comparison on a tensile part specimen. 

Resistance to harsh disinfectants used in healthcare settings is an important property for polymers intended for use in device and equipment housings. Chemical resistance is needed to prevent or mitigate environmental stress cracking (ESC) that can result from repeated exposure to disinfectants.  

To test for the ESC resistance of LNP ELCRIN W1000JiQ resin and its fossil-based counterpart, SABIC used PDI’s Sani-Cloth AF3 Germicidal Disposable Wipes, which incorporate one of the strongest chemicals used on medical devices. SABIC also used Banana Boats Sunscreen lotion (Edgewell Personal Care) to represent an aggressive substance from skin contact. The tests featured tensile bars in continuous contact with these chemicals under 1% strain at room temperature for seven days.  

Table 2 shows that both materials performed very well under exposure to Sani-Cloth AF3 wipes and Banana Boat sunscreen. A positive rating (+) in this table indicates over 90% retention of yield strength and 80% to 140% retention of elongation after exposure, indicating no significant change. 

The industry typically requires healthcare-grade materials to meet stringent criteria, such as biocompatibility pre-assessment; management of change; plant and formulation lock; long-term supply guarantee; and production according to good manufacturing practices (GMPs). Further, each end application has its own set of specific material requirements. 

Samples of LNP ELCRIN W1000JIQ resin from typical production lots have passed certain biocompatibility tests specified by the United States Pharmacopeia or described by ISO 10993, the standard for biological evaluation of medical devices. The tests were consistent with guidance provided by the U.S. Food and Drug Administration (FDA) regarding use of the ISO 10993 standard. 

Potential drop-in solution for traditional PBT

Multiple plastics in a given family, such as PBT, may appear the same. But upon deeper evaluation, variables may come to light. This study looked closely at subtle differences between SABIC’s upcycled PBT material and the fossil-based PBT product from various angles and concluded there were no significant differences between them. 

This analysis indicates that LNP ELCRIN W1000JiQ resin can be considered a drop-in replacement for traditional PBT, offering enhanced sustainability with similar properties and a candidate material for many healthcare applications. Compliant with FDA food contact regulations, including formulation lock, production according to GMPs and a stringent management of change process, SABIC’s product expands options for customers in meeting their goals related to sustainability.