Material considerations for sustainable manufacturing
Izzy de la Guardia, Senior Design and Development Engineer, and Kathleen Bollito, Customer Application Engineer
The journey toward producing sustainable parts doesn’t stop with sustainable design or supply chain practices. Since some materials are more eco-friendly than others, making thoughtful material choices can go a long way toward making manufacturing more sustainable. In addition to reducing your company’s environmental impact, using sustainable materials can help build your reputation as a green business. Plus, consumers are more willing to support environmentally responsible companies.
While many metals can be recycled repeatedly without losing quality, the same can’t be said for plastics. 91% of plastic isn’t recycled, and much of it ends up in our landfills. There’s a lot of room for improvement, so in this first part of our sustainable manufacturing series, we’re going to focus on material considerations for sustainable manufacturing with plastics. There are opportunities to select materials with lower environmental costs associated with sourcing, use, and disposal.
Sustainable sourcing of materials
If you’re trying to make a part more sustainable, looking at where you source your material is a great place to start. First, you’ll need to choose between using a material sourced from a renewable or a non-renewable resource.
Renewable resources vs. non-renewable resources
Renewable resources are natural resources that can be replenished to replace the depleted amount. Sometimes, this replenishment is accomplished through natural production, but other times, we might need to put in a little effort. For example, trees are a natural, renewable resource. However, when we cut down trees in an area faster than they can regrow, we need to plant new seeds and saplings.
Non-renewable resources are finite — once they’re gone, they’re gone. Our supply of many non-renewable resources is dwindling, and many will run out shortly. For example, most estimates predict that we’ll deplete the world’s oil supply in 40 or 50 years if we continue our current rate of oil extraction.
To reduce the depletion of natural resources, use renewable resources as much as possible. In the world of plastics, this means using bioplastics over petroplastics. Petroplastics are produced from non-renewable crude oil, while bioplastics are partially or entirely derived from renewable biomass materials or natural byproducts and are more eco-friendly than their fossil fuel-based counterparts. Common materials in bioplastics include straw, sawdust, corn starch, woodchips, and vegetable oils and fats.
Although you might assume biobased plastics are biodegradable, that is not always the case. For example, “drop-in bioplastics” like bio-PET are chemically identical to the fossil fuel versions, just derived from biomass, so they are not biodegradable, only recyclable. Whether you opt for renewable or non-renewable resource-based plastic, you can further reduce the need for virgin material and make production more sustainable by using plastics with higher recycled content.
Manufacturing with recycled material extends the lifespan of that original material, so you don’t have to source as much virgin material. This can help you reduce your material costs and go a long way toward improving your product’s overall sustainability. After all, producing one ton of products using recycled plastics instead of virgin plastic prevents 1.6 tons of carbon dioxide emissions from entering the atmosphere and saves five barrels of oil.
While metals don’t degrade when recycled, many plastics are not easily recycled or can only be recycled a few times before their physical properties are significantly affected. In many cases, people use a blend of recycled and virgin plastic to maintain acceptable material properties. The most common plastics containing recycled content used in manufacturing include polyethylene terephthalate (PET) and high-density polyethylene (HDPE).
Understanding a product’s end of life
Beyond considering your material source, you’ll want to think about what will happen at the end of your product’s life. Materials can be biodegradable, compostable, recyclable, or some combination of the three (or none!), depending on their chemical composition, so it’s important to understand the differences when evaluating materials.
Biodegradable vs. compostable plastics
Although they are often used interchangeably, compostability and biodegradability aren’t the same. Every compostable plastic is biodegradable, but not every biodegradable plastic is compostable. Compostable plastics, such as thermoplastic starch-based plastic (TPS), polybutylene succinate (PBS), or polycaprolactone (PCL), can break down into organic elements and nutrients that enrich the soil. Biodegradable plastics will decay naturally without harming the environment, but they won’t necessarily break down into organic elements.
Biodegradable plastics fall into two groups — oxo-biodegradable (plastics that break down via oxidation) and hydro-biodegradable (plastics that break down via hydrolysis). Hydro-biodegradable plastics tend to break down faster than oxo-biodegradable plastics but must usually be industrially composted. Compared to hydro-biodegradable plastics, oxo-biodegradable plastics are less expensive, easier to process, and have better mechanical properties.
Not all compostable products are created equal either. Home compostable products will biodegrade in conditions and temperatures in typical homes or compost piles in the backyard. However, industrial compostable plastics usually require sustained temperatures, the presence of carbon- and nitrogen-rich materials, or more air to break down in a reasonable timeframe.
For example, polylactic acid (PLA) requires industrial composting because it will only degrade at temperatures above 136 degrees. However, polyhydroxyalkanoate (PHA) can break down at home. So, although PHA is more expensive and requires more energy to produce, there is a higher probability it composts, as it does not rely on end user disposal to end up at the correct composting facility. If you select a commercially compostable plastic, it’s important to consider how you can promote proper disposal. Consider clear labeling or take-back programs.
If you cannot source a biodegradable option, the next best thing is recyclable plastics. Generally, thermoplastics are much easier to recycle than thermosets, as they can be continually melted and reformed.
The most commonly recycled plastics have an assigned recycling number that tells consumers the plastic’s type and recyclability. Plastics with lower numbers are more easily recyclable than those with higher numbers. Commonly recycled plastics include:
- PET or PETE — Polyethylene terephthalate (PET) is a lightweight plastic that’s easy to recycle and often used in packaging, water bottles, clothing, fiberfill, and rope.
- HDPE — High-density polyethylene (HDPE) is a chemically resistant, easily recyclable plastic.
- PVC or V — Polyvinyl chloride (PVC) is a rigid thermoplastic that’s moderately recyclable.
- LDPE — Low-density polyethylene (LDPE) is moderately recyclable.
- PP — Polypropylene (PP) is tough, chemically resistant, and recyclable.
- PS — Polystyrene (PS) is moderately recyclable.
- Miscellaneous — #7 plastics are non-recyclable.
By labeling your products with the appropriate recycling number, you can help end users understand which plastics are recyclable and how they should dispose of their product. You’ll need to include the product’s recycling number on the product itself (e.g., CNC machining or laser engraving the text onto the product) or relay the information to your consumer in another way (e.g., on the tag or in an instruction manual). Most curbside recycling programs accept the lower numbers, but some cities might not take the higher numbers, so these plastics would need to be recycled through special programs.
In addition to clearly labeling your products, you can establish take-back programs to help extend your material life. Consider offering a mail-back recycling program, a trade-in program, or organizing free collection sites.
Sustainability in additive manufacturing
If you’re looking to incorporate more sustainable 3D printing materials, there are a few options to consider. While using fused deposition modeling (FDM) technology, you can explore filament made of recycled or biobased plastic (like oyster- and wheat-based Francofil filaments) or pellet-based extruders that can directly melt ground-up plastic chips.
Additionally, production systems like HP Multi Jet Fusion are working to minimize their footprint by enabling most excess powder from their builds to be reused in future projects when mixed with a percentage of virgin powder. They also recycle unreclaimed powder and scrap parts to create injection molding stock, as with these production Ford parts.
We still have a long way to go when it comes to sustainability in additive manufacturing, but many companies are taking steps to innovate and improve sustainability. New sustainable materials are also constantly in development, such as algae- and seaweed-based filament and soy-based FilaSoy. Forust uses waste sawdust and bio-based lignin to 3D print wood. It is worth researching what commercially available options may work for your applications and inquiring with your material providers to see what advancements they are making in sustainability.
Sustainability in injection molding and cast urethane
In injection molding and urethane casting, popular waste-saving options include using a material with recycled content or regrinding (feeding the scrap from the injection molding process back into itself). Additionally, it is worth researching if there’s a biobased alternative to your plastic of choice, such as bio-PET or PE made from sugarcane or bio-PC made from corn. You can also opt for sustainable filler materials, such as hemp, coconut shells, rice hulls, and algae, but take care to ensure that they don’t negatively affect the recyclability of your part.
The key challenges of using green materials
Green materials are better for the environment, but using them can be challenging. Take recycled plastics, for example. They often have weaker molecular structures than virgin plastics and will be more prone to breakage. They may also be less resistant to chemicals, impacts, and extreme temperatures, so consumers will need to purchase a replacement sooner than if they’d bought a product made from virgin plastic. In many cases, sustainable alternatives like the bio-based version of common plastics may be more expensive than their commonplace petro-based counterparts. Plus, there are generally fewer sustainable options commercially available, so it’s important to continue to push innovation in this field and put pressure on material providers to develop and offer less harmful materials.
Choosing sustainable materials with Fast Radius
There’s a lot to think about when choosing a material for your next project, especially when it comes to sustainability. These days, there are plenty of sustainable materials used in manufacturing, but it can be challenging to determine whether you need something biodegradable, compostable, recyclable, or altogether different. An experienced manufacturer can help.
When you partner with Fast Radius, our team of experts can guide you through the material selection, helping you make the best decision for your project. Contact us today to get started, and keep your eye out for more sustainability best practices from our Fast Radius team.
Visit our resource center to learn more about manufacturing with recycled materials, creating a sustainable future with cloud manufacturing, and more.