Classroom
Open source education is a wonderful, accessible form of knowledge sharing; however, when approached without a structure it has the potential to feel disjointed and confusing. Below is some of the structure I created for myself to form the framework for DIY material education.
Throughout this site, I will often use the terms biomaterial and bioplastic interchangeably. Most of the recipes are bioplastics with a variety of bio-based fillers (for example, a gelatin-based bioplastic with the addition of coffee grounds for structure). However sometimes I used the word biomaterial if the end result isn’t what we normally associate with a ‘plastic’ material (for example, oyster shell “marble” or pine rosin).
That said, biomaterial is a vague term that can encompass a wide world of bio-based materials. Below is a helpful diagram adapted from the Biofabricate report Understanding ‘Bio’ Material Innovations to understand terminology.
For example, bioassembled materials are inherently biofabricated materials but not all biofabricated materials are bioassembled (some are made from biofabricated ingredients).
You’ll notice that bioplastic isn’t listed on that diagram at all, so…what is a bioplastic?
Bioplastics are polymers with similar physical properties as fossil fuel-based plastics but derived from renewable biomass sources. They rely on biopolymers rather than petroleum-based polymers.
Actually, the definition of a “plastic” is simply a compound produced by polymerization. Due to the ubiquitousness of fossil fuels, the term has become shorthand for petroleum-based polymers whereas biopolymers now have to be modified as bio-plastics.
Bioplastic: a polymer derived from renewable biomass sources, such as vegetable fats and oils, corn starch, cellulose, food waste, etc.
Biopolymer: a natural polymer produced by the cells of living organisms, such as gelatin, cellulose, starch, alginate, etc.
While bioplastics and biopolymers seem like the same thing, they cannot be used interchangeably. Consider this: DNA consists of pairs of biopolymers (polynucleotides) but you would never say DNA is made of pairs of bioplastics.
In general biopolymer refer to the macromolecule structures that form the backbone of most bioplastics while bioplastic refers to the processed material.
Since most of the recipes on this site are a variation of bioplastic, it is helpful to introduce the basics of what makes a bioplastic. A general recipe for making a bioplastic is to combine one or more biopolymers, plus plasticizer, plus any additives.
A Basic Recipe
Biopolymer(s) + Plasticizer(s) + Additive(s) = Bioplastic
Obviously the choice of biopolymer(s) will dramatically affect the mechanical properties of your bioplastic. Below are the five main types of bioplastics, which are generally sorted based on the biopolymer type.
5 Main Types of Bioplastics
Starch-Based: Most popular form of bioplastics and generally the cheapest. Often used for drug capsules and utensils.
Cellulose-Based: Utilizing the structural component of plant cell walls, cellulose-based bioplastics are usually more water resistant than starch-based.
Protein-Based: Bioplastics made from proteins such as wheat gluten, casein, and gelatin. Can often be sourced from either plant or animal origins.
Bio-Derived Polyethylene: PE produced from the fermentation of raw agricultural materials like sugarcane and corn rather than fossil fuels.
Aliphatic Polyesters: A group of synthetic biodegradable polymers made from lactic acid, glycolic acid, lactide, glycolide and ɛ-hydroxycaproic acid (PLA, PHB, etc.).
Beyond being grouped by biopolymer source, the world of bioplastics can be divided into thermosets and thermoplastics. Fossil fuel-derived plastics are also divided in this way as it has to do with the chemical bonds formed during the process of polymerization.
Thermoset: polymers that form permanent cross-links during the curing process. These have higher stress tolerance than thermoplastics and are immune to re-melting under high heat.
Thermoplastic: polymers that do not form permanent cross-links when curing or cooling. These can be remolded under the right conditions but have lower stress tolerance than thermosets.
Hopefully this gives you a fairly good start for understanding bioplastics and where they fit within the biomaterial landscape. For instance, I know that my Biolaminate recipe is a protein-based bioplastic which relies on the biopolymer gelatin. I know that it is thermoplastic, meaning it could be remelted and reformed if necessary. The base recipe is readily biodegradable and home compostable, although not vegan since the gelatin I use is sourced from fish.
Below are links to further resources, including an entire Resources page full of helpful references.