Updated: Jun 7, 2021
The question was: "If hemp can do everything plastics can do, can someone provide an example of the exception, what hemp can't do, or plastic does better?"
That is a great question!
Hi, my name is Dr. Ron Kander at Thomas Jefferson University and here is my quick answer.
Hemp has quite a few advantages as a highly sustainable source of biomass that can be used as a feedstock in making a wide range of industrial and consumer products. One potential use of hemp is as a raw material in making biodegradable polymers, or as a biodegradable reinforcing agent in polymers (either in traditional polymers or in biodegradable polymers). In fact, reinforcing hemp-derived polymers with hemp-derived fibers can produce a biodegradable composite material with attractive mechanical and physical properties. The sustainability and biodegradability of hemp-derived polymers and composites is balanced, however, by the fact that, currently at least, these materials tend to have higher costs and somewhat lower mechanical and physical properties as compared with traditional polymers.
Traditional polymers are made from hydrocarbons that are typically derived from natural gas, crude oil or some oil derivative (like tar sands). The key advantage of typical polymers and polymer-based composites (the ones we use in consumer goods) is their light weight, toughness and relatively low cost. (Although, there are some very expensive high-performance polymers in applications like aerospace and defense.) Traditional polymers are relatively easy to mold into complex shapes, have reasonably good mechanical properties (not as good as metals and ceramics, but good enough for a wide range of applications) and they have great durability in a wide range of environments.
It is this last property that is the Achilles heel of biodegradable polymers and composites (whether made from hemp or some other biomass like corn, wood or soybean). The simple fact that these materials are biodegradable (which is good) means they break down by bacterial decomposition over time. This means they will not be as durable as traditional polymers and composites in typical consumer environments (like water, UV light, heat, oxygen, etc.).
So, hemp-derived polymers have many advantages, but are outperformed by traditional polymers when it comes to cost, mechanical properties and long-term durability. Research and development efforts can reduce costs and improve mechanical properties, but it will be difficult to address the long-term durability problem if we want the material to remain biodegradable.
So, this is Dr. Ron Kander, and that was my quick answer to a very good question.