Plastics. What comes to mind when you hear that word? Unfortunately for many people, it’s some version of this image. We’ve been haunted by images of overflowing landfills and polluted natural environments filled with containers, packaging, and inexpensive consumer goods that, by design, have extremely short lifetimes.
In most cases, that lifetime is single-use, after which they are discarded. But the public perception of environmental waste doesn’t reflect the reality of all plastics. When we talk about environmental impact, not all plastics are created equal.
While some types of plastic are undoubtedly part of the problem, others are actually part of the solution.
The vast majority of plastic waste is thermoplastic. Materials such as polyethylene terephthalate (PET), polyethylene, and polyamide (nylon) are among the most commonly used to produce single-use items, including packaging and beverage bottles.
These materials are lightweight, inexpensive, melt-processable, reprocessable, and easy to mold into a wide range of shapes. But this versatility is a double-edged sword. Because items such as blow-molded thermoplastic beverage bottles are inexpensive and easy to replace, they enter the waste stream after a single use.
While some thermoplastics are recyclable, only a small portion enters the recycling stream. Beginning in the 1980s, municipal recycling programs appeared to offer a means of simultaneously reducing the environmental impact of single-use thermoplastics and landfilling.
However, even the best municipal recycling programs have only a minimal impact on curtailing plastic waste. On average, only 9% of plastics collected through such programs are actually recycled. The rest ends up in landfills and incinerators. The recycling process is expensive and resource-intensive, and typically yields materials with inferior physical properties compared with their virgin counterparts.
Standing in contrast to thermoplastics are thermosets. Thermosetting plastics like unsaturated polyester, vinyl ester, and epoxy resins retain their strength and shape when heated. They also possess high strength, often comparable to that of less versatile materials such as metal or concrete, and can be fabricated into a wide variety of shapes and sizes.
Unlike thermoplastics, most items made from thermosets are not intended for a single-use. Their high chemical and weathering resistance, thermal stability, and mechanical properties make them well-suited for long-term use across a wide range of applications and environments.
A recent study ranked the potential environmental hazard associated with waste plastics. The largest contributor to global waste was polyethylene (PE), accounting for 97 million tons per year, with polypropylene (PP) second at 55 million tons and PET third at 32 million tons. PE, PP, and PET are thermoplastics that constitute the vast majority of single-use consumer goods.
Of the 36 materials most commonly entering the global waste stream, only 4 are thermosets. The combined total of all thermosets entering the global waste stream was 8.05 million tons. Compare that with 184 million tons of PE, PP, and PET thermoplastic waste generated each year. These numbers indicate that, because they are ideal for long-term use, thermoset plastics enter the global waste stream at a substantially lower rate than thermoplastics.
There’s also the question of what happens when these materials enter the environment. Due to the sheer volume of plastic waste, there is substantial leakage of plastics from the global waste stream into the environment. Perhaps the most familiar example of this is the Great Pacific Garbage Patch, a swirling vortex of marine debris in the North Pacific. The patch is made up primarily of tiny bits of plastic called microplastics.
The decomposition of plastic waste into microplastics in marine environments is directly dependent on density. The two most common thermoplastic waste materials, PE and PP, are less dense than water.
When waste plastics have a density lower than that of water (approximately 1.0 g/cm3), they float to the surface, where they are subject to biodegradation, UV degradation, and mechanical wear from waves, currents, and other forces. This creates microplastic particles that become floating marine debris, which eventually aggregates into formations such as the Great Pacific Garbage Patch.
Unlike PE and PP, most thermoset materials are denser than water. For example, unsaturated polyester typically has a density of around 1.12 g/cm3. Thermoset materials are often combined with fillers and other reinforcing agents, such as glass and carbon fibers. The presence of these reinforcing materials in products such as fiber-reinforced plastics (FRPs) further increases their density and reduces their susceptibility to degradation.
When thermoset products enter the environment, their higher density causes them to sink, thereby reducing the potential for human exposure. These denser materials settle on the seabed, where their surfaces are colonized by bacteria and algae. The coating of bacteria and algae shields their surfaces from UV degradation and mechanical wear, leading to a dramatic reduction in degradation.
This means that thermoset materials are far less likely to be transformed into plastic microparticles, and even when degradation does occur, their higher density causes them to settle to the seabed.
As we’ve already learned, a far smaller proportion of the global waste stream is generated from thermosets compared to thermoplastics. We also know that when thermosets enter the environment, their impact is much lower than that of less-dense thermoplastics such as PE and PP. What else can thermosets do to minimize environmental impact?
We’ve all heard the 3 R’s: Reduce, Reuse, Recycle. While thermoplastics can be recycled, only a small portion of these materials (approximately 9%) actually enter the recycling stream. We also know that because most thermoplastic products are intended for a single-use, they aren’t often reused.
Because they are single-use items, they don’t reduce the amount of waste generated and, in fact, have the opposite effect, encouraging increased production of disposable goods. So thermoplastics get a failing grade on all three Rs.
Thermosets are not typically considered recyclable materials, although this is rapidly changing. Thermosets like unsaturated polyester can be chemically recycled - converted back into raw materials or monomers - and used to manufacture new products.
Because of their outstanding physical properties and durability, thermoset and FRP products are designed for repeated use over an extended service life. Even in highly corrosive environments, such as hydrochloric acid storage tanks, FRPs have in-service lifetimes exceeding 20 years. This has the combined effect of encouraging repeated reuse and reducing the quantity of waste thermoset material entering the waste stream.
Even disposed thermoset products can be reused or repurposed. Fiberglass from thermoset FRP can be removed and converted into filler materials used in composites. FRP itself can be crushed or granulated and used as filler in applications such as building materials. Thermosets also help extend the service life of aging buildings and infrastructure by retrofitting with FRP to enhance structural stability.
Thermosets clearly receive a passing grade on at least two R’s - reduce and reuse - and efforts are currently underway to improve the recyclability of FRPs and other thermoset materials. It’s also apparent that the environmental impact of thermoset materials, such as fiber-reinforced plastics, is significantly lower than that of thermoplastics.
There’s much we can do to reduce the amount of plastic waste we generate and the environmental impact of that waste. Favoring more durable, multi-use materials like thermoset plastics over single-use thermoplastics can go a long way toward achieving those goals.
If you’re considering reinforced thermoset materials like FRP for your next project, contact our team. We would love to help you learn more about how Tencom’s line of products can help.