Monday, April 15, 2024

Kicking the plastic habit 2 - What about Silicone or Rubber?

 Kicking the plastic habit - What about Silicone or Rubber?

In my previous post, I neglected to mention two other materials that might replace some plastic use - silicone and rubber. Are they any better?

The short answer is yes, but with some important qualifications. Neither is made from fossil fuels, and so that is a plus.  Both are less toxic to us and our environment, and neither breaks down into fine particles like microplastics. 'll deal with silicone first.

Silicone is a rubber-like material that is actually made from plain old silicate sand (SO2), as is glass. There are many silicone products that could replace fossil fuel-based plastics, including multiple-use stretchable bowl covers that can replace plastic wrap for saving dinner leftovers. There are also silicone baby bottles, water bottles, mugs, etc. not to mention spatulas and other utensils that take advantage of silicone's high heat resistance. So, sounds like a pretty good deal, right?

Maybe. A significant factor in evaluating any technology is the degree of processing involved. A longer, multi-step manufacturing process is likely to require more energy and result in more pollution. Cutting a piece of bamboo culm to use as a drinking cup is far more environmentally friendly than extracting the cellulose from the bamboo and then using it to make socks (see the process for making viscose in my previous post. 

Glass is essentially sand that has been melted and re-shaped. It takes a little heat, but is a simple process that has been used for centuries. Silicone, however, is a much more radical transformation of sand. Like carbon, silicon atoms have four bonding sites, so have a similar ability to form long polymers with varied side chains.  Intense heat (around 1000 degrees Celsius) is required, however, to remove the oxygen from silica molecules, transforming it into pure silicon.  The silicon is further processed, with more heat, to make it form plastic-like polymers.  The heat required is generally derived from fossil fuels. 

The amount of energy required to make one kilogram of silicone is roughly11 kilowatt hours, the equivalent of 5 kg of coal, or nearly a gallon of petroleum. Roughly the same amount of fossil fuel is needed to make a kilogram of plastic. So the consumption of fossil fuels is about the same for silicone as it is for plastics. Making silicone puts carbon dioxide into the air, while making plastics solidifies it into the stuff that litters the oceans and our water supply. Both problems can be addressed, but the track record so far is not good. Once again, one must look for responsible producers when considering silicone products.

The starting ingredient for both glass and silicone is abundant, but the mining of sand, potentially defacing the landscape and disrupting local ecosystems, is a factor to be considered in the eco-friendly equation. Glass is a better use of sand, and can be recycled over and over. It appears that silicone is non-biodegradable, or at least takes a very long time to break down. So, like plastics, it must be safely buried at the end of its useful life. In the end, silicone has an edge over plastics in that it is less toxic and does not break down into microplastics. 

In the rubber tree, Hevea brasiliensis, latex
drips freely from cuts in the bark, a process
called tapping, which does not harm the tree. 
Photo by Vis M, CC BY-SA 4.0.
What about real rubber? Natural rubber has the potential to do a lot of what silicone and plastics do, but is plant-based and biodegradable. Rubber comes from the sticky latex formed by certain trees and herbaceous plants.
The function of latex for the plants themselves is generally said to be as defense against insect damage. 

The primary commercial source  of latex is the rubber tree, Hevea brasiliense, in the Euphorbiaceae (Spurge or Poinsettia family) but many  members of the Fig Family, (Moraceae), also produce latex, as do members of the Milkweed Family, and others. Dandelions (Asteraceae, or the Sunflower Family) were grown during World War II as an alternate source of latex, when America and its allies lost access to the commercial rubber plantations of Southeast Asia. The cultivation of dandelions for latex is being revived as a more environmentally-friendly alternative to rubber plantations.

Rubber from natural latex sources can replace plastics and silicone in many applications, and is biodegradable, though depending on how it has been processed it may take many years to decompose. Rubber that has been vulcanized to make it more durable, breaks down much more slowly than raw latex or minimally processed rubber.  There is experimentation with bacteria that can speed up the decomposition of rubber. Of course, synthetic rubber is a different story altogether, as it is made, like plastic, from fossil fuels. 

Processing latex in the field and conversion to rubber products in factories are, of course, potential sources of pollution. There are ways to minimize such problems, and consumers can choose products that have been responsibly manufactured.

The biggest potential problem with rubber is that the rubber trees are generally grown in massive plantations, resulting in the usual disease and pest problems associated with monocultures, along with   deforestation and the loss of biodiversity. Similar problems plague palm oil plantations, and indeed most modern agriculture. The cutting down of biodiverse rain forests for rubber or oil production, seems somehow more egregious than replacing grasslands with wheat or corn. 

A better way to grow rubber is through mixed plantings with other crops. It is compatible with growing other tree species for wood, cellulose, fruits or nuts, or for intermixing with low-growing shade-tolerant crops. Such farming can be as profitable as monoculture plantations. It is similar to how indigenous peoples originally harvested rubber directly from wild-growing trees in the forest. 

Bottom line, silicone, and even better, natural rubber, can be considered options for limiting our use of plastics derived from petrochemicals, if the energy and environmental impacts can be mitigated. Once again, with so many people on the planet, there is a cost to whatever technology we use. We can only choose the lesser of evils. 

Sunday, April 7, 2024

Kicking the plastic habit with a little help from plants

 I was recently on the expedition class Viking Octantis for a cruise along the Chilean coast. The ship staff included a team of scientists and naturalists who were actively investigating environmental changes in the oceans while engaging and educating the ships passengers.  One lecture dealt with the issue of plastics in the oceans, which now pollute even Antarctic waters and coastlines. That sobering lecture was the inspiration for this essay.

We live in a plastic world. Plastics are durable, inexpensive, and convenient. From plastic water bottles, packaging, and shopping bags to durable kitchen gadgets and automobile parts, plastic products derived from fossil fuels have made life more convenient and less expensive. HOWEVER, from start to finish - from the extraction of fossil fuels to the manufacture of plastic products to their eventual disposal -  the use of plastics poses serious risks to the environment, wildlife, and our own health. 

A sea turtle entangled in a fishing 
net. Photo by Doug Helton.
The primary problem with plastics is that they never go away. Plastic production accounts for about 6% of fossil fuel use, a small amount compared to what is consumed for automobile, aircraft, and industrial fuels, but because of their near indestructibility, the volume of plastics on our planet builds up year after year.  According to a recent study (Li et al., 2023) the amount of plastics produced annually (as of 2019) was a staggering  460 million tons, of which only 9% is recycled. 

The remains of an albatross with stomach full
of plastic debris. photo by Forest & Kim Starr (USGS)
Regrettably, much of this plastic ends up in the oceans, where it can persist for hundreds of years. In 2014 there was one pound of plastics for every five pounds of fish in the oceans worldwide. Plastic water bottles and conventional disposable diapers can last up to 450 years in the sea. Marine mammals, sea turtles and birds get tangled in the debris and drown, or starve to death when their guts get clogged with plastic debris. 
Microplastics are everywhere.

But that's only part of it. While chemically indestructible, much of the plastic debris eventually breaks down into finer and finer particles, what are referred to as microplastics. These fine particles can be taken up by filter-feeding plankton, shrimp, and krill, and then move up the food chain.  Ongoing research is showing that microplastics in our food and water can harm human health (Li et al., 2023).

The major synthetic fabrics used today, polyester, nylon, and acrylic, are highly valued for their smooth feel, resistance to wrinkling, and quick-drying properties,  In addition to their eventual arrival at a landfill, every time such fabrics are washed in your home washing machine, tiny bits of fiber break off and add to the microplastic load in our water supply. 

Cleaning up the mess that is already there, and proper disposal of future plastic waste represent a huge challenge.  There is a glimmer of hope with the discovery of bacteria that can digest plastic. They potentially could help with disposal and the cleanup effort, but so far have not been used on a practical scale. 

Silkworms feed on mulberry leaves and excrete silk
filaments to make a cocoon. This natural process is
analogous to making viscose, but without the harsh
Photo cc Fastily at English Wikipedia
To slow the accumulation of plastics, and maybe even stop it, however, we can turn to natural biodegradable alternatives. Animal products, like wool, leather, etc., can take up some of the slack, but plants can provide  an even more massive source of organic building blocks to replace fossil fuels. The unique plant compound  cellulose, which strengthens cell walls, fibers, and wood, can effectively replace fossil fuel feedstocks in almost any application. Plants have always long provided us  with natural fibers from cotton, linen, and silk (the latter with a little help from a  caterpillar!). If we can shift back more to these natural fabrics, we can make a big difference.

Other cellulose-based products that have been with us for over a century are plastic-like celluloid, cellophane, and rayon.  Celluloid was formerly used to make billiard balls and other solid objects, as well as movie film. Its use was discontinued due to its unfortunate tendency to explode or catch fire upon impact. Cellophane and  rayon, continue to be in use, but have their own associated hazards.     They are made by treating cellulose with harsh chemicals to make a mush that can be extruded through tiny pores to slender soft fibers, or through thin slits to make cellophane sheets. Fabric fibers made in this way are called viscose. The handling and disposal of the chemicals used in this process are bio-unfriendly, if not done carefully. Before purchasing such products, including those puzzlingly soft bamboo socks, one should check whether the manufacturer is environmentally responsible.  

Modern bioplastics have been devised to avoid these problems. One cleaner process converts the plant cellulose into lycocells, similar to viscose, but using less chemicals. Tencel is a product made in this way. There are now many commercial ventures starting to manufacture environmentally-friendly, plant-based bioplastics including styrofoam-like materials, other packaging materials, and even biodegradable disposable diapers. If these catch on, we can significantly shift away from plastics. 

Bamboos are the poster child for fast-growing 
sources of cellulose. New stems are continuously
produced from underground rhizomes, and can
grow up to 3 feet per day.
The cellulose for these processes can be extracted from a variety of sources,  Fast-growing trees, like EucalyptusCasuarinaPopulus, and Paulownia, along with bamboo and sugar cane stalks, can be grown like other agricultural crops, as a source of cellulose. 

Eucalyptus harvest in Cameroun. Eucalyptus  is
native to Australia, but has been widely planted in
warm parts of the world as a source of wood and cellulose.
It unfortunately often becomes invasive, displacing native 
vegetation. Photo by Jean-Louis Heckly, cc Wikipedia
Cellulose, of course comes in premade forms like wood and bamboo. Wood can be carved into almost any shape: spoons, spatulas, bowls cups, toys, toothbrushes, etc., for which cheaper plastics are often used today. In traditional and modern technology, bamboo culms can be cut and used directly for housing, flooring, scaffolding, water pipes, containers, paper, and hundreds of other structural materials. 

The drawback to wider use of cultivated bamboo and other cellulose sources is that it requires more land to be converted into agriculture, diminishing the biodiversity of natural plant communities, and creating disease and pest-prone, fertilizer and water consuming monocultures

With so many people on the planet, there is no technology that is without environmental cost, but overall, cultivating biodegradable cellulose sources, if done responsible, is far better than continuing to load our oceans and drinking water with plastics. 

The plastic problem seems overwhelming, and much of the solution will have to come from government legislation and reform of manufacturing processes, but individuals can take small steps that will make a difference.  Can you commit to one or more of the following?

1. Use less clothing made of synthetic fabrics and go back to cotton and other natural plant based fabrics. Use an iron if wrinkles offend you!

2. Support emerging bio-friendly technology, including environmentally-friendly diapers, whenever available to replace plastics. 

3. Trade in your plastic toothbrush for one made of wood and natural fibers.

4. Use glass, stainless steel, wood, or bamboo-based kitchen utensils, bowls, storage containers, etc. instead of plastic ones. 

5. Filter your own water and use glass or stainless steel containers for carrying it around.