By Tabitha McLeish
A couple of months ago I was blessed with the news that I am becoming a grandmother. My very first grandbaby! I am exploding with happiness and my heart is full. And although I'm over the moon, I must confess that I’m also very concerned about the consequences of the world’s two biggest environmental crises, climate change and plastic pollution, and how they may affect my grandchildren, their children, and the generations beyond them.
The world continues to experience dramatic and unpredictable effects related to climate change in the form of record high temperatures, more frequent extreme weather events, megadroughts, destructive wildfires, melting glaciers, and rising sea levels. Increasing plastic production is a leading factor in overflowing landfills, negative impacts on human health, and polluted oceans which negatively impact marine life. Environmental scientists project that the equivalent of 700 billion plastic water bottles end up in our oceans every year, and unless drastic action is immediately taken, the amount of plastic may outweigh fish by the year 2050. I cannot fathom what life might look like if significant progress isn’t made in reducing plastic pollution and slowing greenhouse gases to mitigate climate change.
There is no question that these two issues require real-time innovation and action to minimize the impact they will have on future generations. The coatings and materials industry has a crucial role to play in the development, delivery, and adoption of innovative sustainable solutions which provide a pathway to circularity and reduced carbon emissions.
Powder coatings, in comparison to traditional liquid coatings, have long been recognized as an environmentally friendly and sustainable coating option. These coatings contain no solvents, making them free of hazardous air pollutants (HAPs) and little to no volatile organic compounds (VOCs), are easy to apply, and provide high quality durable finishes. Powder coatings also have excellent transfer efficiency and overspray can easily be reclaimed for reuse or recycling. Historically, the term “environmentally friendly” indicated pollution reduction or prevention. However, over the years, the overall concept of sustainability within the coatings industry has evolved and broadened to account for every stage of a coating’s life cycle (raw material extraction and manufacturing, formulation, manufacturing, application, product use, end-of-life disposal) and its total effect on the environment, society, and economy.
The coating industry’s continued advancements in powder technology make it possible to expand the sustainability focus to include:
- Elimination of materials of concern for safer use.
- Production efficiency improvements (lower and/or faster cure times reducing the amount of energy consumed).
- Waste reduction (sending less material to landfill).
- Improved coating durability to lengthen the time of an asset’s in-use life (extended color/gloss retention, corrosion, scratch resistance, etc.).
- Reduction of carbon footprint.
- Increased use of sustainable feed stocks (bio based or recycled).
While all these attributes contribute to increased sustainability, there are three gaining significant momentum and driving toward a circular economy:
- Use of renewable materials.
- Powder waste reprocessing.
- Circular resins made from recycled plastic.
Bio-based Materials
Most raw materials in coatings on the market today are made from fossil-based feedstocks. In a more climate-friendly world those components would be derived from bio- renewable materials instead. The use of bio-based building blocks offers industry a path to increased sustainability in powder coatings, albeit the market for these coatings is currently estimated to be very small.
Some factors that are driving interest in bio-based coating development include greater price stability, reduction in greenhouse gas emissions, and finite reserves of petrochemical-derived raw materials.
Resins have the greatest potential for using “drop-in” bio-based materials which are chemically identical to their petrochemical counterparts. Historically, petroleum- based resins have long been favored for use due to their availability, wide range of performance properties, and cost competitiveness. So far, bio-based powder coatings aren’t largely popular. The costs of making bio-based raw materials are still higher than conventional raw materials, and matching mainstream powder technology performance remains a challenge. Commonly, the bio-renewal products have been inferior in color stability and UV durability. If not overcome, these shortcomings truly are show-stoppers.
Furthermore, it is important to understand that bio-based is not automatically synonymous with sustainable. How plant-based materials are produced undoubtedly influences environmental impact. Growing more crops to support demand for industrial products could adversely affect farming density, arable land use, and watershed runoff of fertilizers. Lastly, if the feedstock was also used for human or animal nutrition, the bio-based ingredients could be in competition with the food chain.
Despite the shortcomings, research and development in this area is becoming a major focus. Adoption of bio- based resins and coatings will only occur if those coatings demonstrate equivalent performance to existing technologies on the market, are scalable, affordable, and truly sustainable.
Concept of Mass Balance
Mass balancing is a faster way to integrate bio-based feed stocks into the value chain, without the need for large investments in upstream infrastructure and processes. It involves the mixing of fossil and recycled (or renewable) raw materials, while keeping track of their quantities and allocating them to specific end products. The actual carbon molecules in the product may not be recycled or renewable, but through a third-party certificate, the renewable content is verified. Because alternative raw materials can be flexibly adjusted, production and demand can grow together without fear of negatively impacting product quality and products contribute to a circular economy.
It can be difficult, however, for end users to grasp the allocation practice and “fuzzy” accounting. Industry standards will be needed to ensure that all product claims are verifiable and prevent green washing.
Recycling of Waste Powder
There has been a long pressing need in the industry for efficient recycling of waste powder coatings. At an increasing rate, coating manufacturers and applicators are establishing zero-landfill policies and are discovering that powder coating can be a very large-volume waste byproduct for which it is difficult to find an outlet. This means that the amount of waste powder coating ending up in landfills each year due to lack of recycling alternatives is astonishing and detracts from the environmental benefits of powder coating.
Examples of waste powder coating include reclaimed fines, spray to waste material, or manufactured product that is off-spec or past its expiration date. To add to the complexity, often the waste is a mixture of different chemistries, colors, surface profiles, glosses, and particle sizes because there aren’t collections systems in place to separate the waste.
A solution to landfill now exists in the form of companies that are dedicated to the recycling of waste powder coating. With specialized equipment and proprietary technology, companies can utilize the waste powder as a raw material and then reprocess it into a high quality custom color matched product per the client’s needs.
The benefits of recycling waste powder coatings are very clear. Recycling eliminates waste from the supply chain keeping it out of landfills, contributes to a circular economy, and helps manufacturers and applicators meet sustainability goals.
Coatings Containing Recycled Plastic
The third route gaining momentum toward a circular economy includes the incorporation of recycled plastic into powder coating resins. With this technology, plastic waste is converted into sustainable, high-performing powder coatings which meet and/or exceed the performance characteristics of existing systems while achieving a full range of color, gloss, or effect.
Using concepts of a circular economy helps reduce plastic pollution, while using somebody else’s waste and reusing it as one of the core raw materials. Also, life-cycle assessments show that these coatings have a substantially reduced environmental footprint, including CO2 emissions reduction, as compared to standard coatings.
PET, or polyethylene terephthalate, is a highly recyclable plastic resin and a form of polyester that is commonly used as a packaging material due to its strength, transparency, and thermostability. It is easily recycled because its polymer chain breaks down at low temperatures, so there is no degradation of the polymer during the recycling process.
Circular polyester resins can be synthesized using pre- consumer or post-consumer plastic waste. Pre-consumer refers to the plastic waste that was created during the process of manufacturing some sort of good prior to its delivery to a consumer. Post-consumer plastic waste is the empty PET packaging that is discarded by a consumer after use, such as water bottles.
Pre-consumer or post-consumer plastic materials are sorted from other recyclables at a material recovery center and sent to a PET recycling facility. The plastic waste is then ground into flakes, further separated based on purity, washed, rinsed, and dried. An extrusion process melts the material, which is then passed through a series of screens to form uniform-sized pellets. The rPET (recycled PET) pellets can be used in the synthesis of circular polyester resins.
A full range of powder coating platforms can be built from resins that incorporate recycled plastic into backbones and include polyester TGIC and TGIC-free, polyester epoxy hybrids, and polyester urethanes. Differing percentages of recycled plastic can be incorporated into the resins, with up to 30% being most common. The sustainability value proposition and the coating performance requirements must be optimally balanced. The recycled content and reduced carbon footprint can help contribute to LEED credits and support Scope 3 carbon reductions.
The key sustainability aspects can be translated into clear value propositions for end users to better visualize the positive impacts. The amount of recycled plastic in a pound of finished powder coating can be converted into the number of plastic bottles and the carbon emissions avoidance converted to a representative number of cars removed from the road.
Consistency and quality of incoming PET materials need to be tightly controlled, so as not to adversely impact coating performance or color, which adds a level of complexity to the value chain and increases cost. It will be important to keep an eye on availability in the marketplace since rPET is widely used across many different industries.
The Journey Ahead
Forces of change are creating sustainability's momentum, driven in part by the evidence of global warming and plastic pollution, and furthered by regulatory pressures, societal demand, and corporate ambitions for carbon neutrality. There have been some interesting raw material advances, powder coating developments, and partnerships improving coatings sustainability; however, the journey ahead is still long.
As a coatings industry, we must strive to collectively develop effective solutions that accelerate the reduction of carbon emissions and tackle plastic pollution, creating a more sustainable future for all. How we choose to respond in the coming years will have massive repercussions for generations to come.
Are you in? I know I am!
Tabitha McLeish is global marketing director-powder, general industrial coatings for The Sherwin-Williams Company.