Some clients are conscious of their products’ impact on the environment. They might add a requirement to specify a material that is recyclable by municipal systems. This is a reference for engineers when considering recyclable plastics in products.

Plastics degrade very slowly or are non-biodegradable in nature. Plastic that has been discarded and may exist for thousands of years. Burning plastic releases harmful toxins into the air polluting the air. Also, the manufacturing of plastics often generates large quantities of chemical pollutants that are harmful(1).

The debate about environmental impact can be complicated at times. The intent of using recyclable plastics can often be one or both:

1. Selecting a material that is biodegradable or degrades while releasing less green house gasses as it breaks down.
2. Selecting a material that reduces the effect on the environment by using renewable/sustainable sources instead of those derived from fossil fuels.

There are also medical materials, like PLA (Polylactic Acid), which are bioresorbable.

Plastic identification codes

Plastic parts are often embossed or debossed with standardized icons to indicate their material. The purpose of this is to aid sorting at recycling facilities.

Recyclable Injection Moldable Plastics

Recyclable plastic selection from Worldchanging.com

Plastic Resins from Cal.gov

Biopolymers

• Bioplastics are made from renewable plant derivatives and not petroleum.
• Some are biodegradable, but not all.
• Although cost is reducing as economies scale, it is often still true that these materials are more expense than commodity plastics.

Polyolefins

• Polyethylene (PE),
• Polypropylene (PP), i.e. containers for food such as butter, yogurt, frozen meal trays, disposable cups.
• High density PE (HDPE), i.e. milk jugs, 5 gallon buckets.
• Probably the easiest selection
• Commodity, petroleum based polymer
• Recycling codes 2, 4 and 5
• Low Density PE (LDPE), i.e. cellphane wrap, diaper liners, grocery bags. Not commonly recycled

Polyester

• PET, most commonly recycled (i.e. 2 Liter soda and other plastic bottles)
• Releases more toxic chemicals than polyolefins
• Still recyclable, code #6

ABS and Polycarbonate

• ABS, PC, and ABS/PC blends, i.e. electronic housings, lenses, clear panels.
• Used in many consumer product applications
• Both are recyclable but not by municipal systems. Recycling code #7 “other”.

Polystyrene

• PS, i.e. “styrofoam”, coffee cups, take-out packaging, packing peanuts, egg cartons.
• Recyclable as code #6, recycled in some areas.

Polyvinyl Chloride

• PVC, i.e. rigid piping
• Uses plasticizers
• Recycling code #3, but often not recycled

Mixed Resins

Blends are not typically recycled

When selecting a material it is worth considering that the recycling process is labor intensive. Materials need to be identified and sorted. Not all materials can be mixed for reprocessing. As such, it is often more effective to select materials for your products that are made of a single material (or easily separable). It is also efficient to utilize materials for which there already exists an infrastructure to recycle, such as PP/PE.  This is the same principal behind selecting COTS (common off the shelf) fastener types and sizes.