Green Chemistry in Action: Choosing the Right Materials PDF

# Green Chemistry in Action: Choosing the Right Materials Green chemistry is a fairly new practice. By understanding the bonding and structure of compounds, chemists can predict their properties and determine their uses. In the past, chemists developed products without considering their effects on...

# Green Chemistry in Action: Choosing the Right Materials Green chemistry is a fairly new practice. By understanding the bonding and structure of compounds, chemists can predict their properties and determine their uses. In the past, chemists developed products without considering their effects on the environment. The practice of "green chemistry" involves the invention, design, and use of products and processes that have a minimal environmental impact. ## The Aims of Green Chemistry | Aim | Description | | -------- | ------------------------------------------------------------------------------------------------------------ | | Sustainability | Starting with renewable materials rather than non-renewable materials (such as fossil fuels or mined materials) | | Safety | Using and producing less toxic chemicals | | Process Efficiency | Using simpler reaction processes with fewer steps | | Energy Efficiency | Carrying out processes at lower temperatures or turning waste into usable energy | | End-of-life Degradation | Designing products that degrade into harmless substances after use | ## Sustainable Materials: Bioplastics To develop a green alternative, companies begin by considering what raw materials they need to produce their products. Research chemists attempt to choose renewable raw materials. They also aim to create a product that functions efficiently and presents no risk to human health or to the environment. Every stage of product development and production should be environmentally safe, including the handling of any by-products. The manufacturer should also consider what happens to the product at the end of its useful life. Most plastics are petrochemicals produced from fossil fuels. These plastics are non-biodegradable but many can be recycled at the end of their product life. Bioplastics, on the other hand, are plastics made from chemicals derived from plants such as corn, potatoes, and peas. The plastic cup in Figure 1 is manufactured under the name "Greenware." It is made primarily from Polylactate (PLA), which is synthesized from corn. The Greenware cup is marketed as "green" because it is compostable. This means that the cup will break down in a regulated industrial composting facility. Typically, at 55°C and 90% humidity, microorganisms first break the intermolecular bonds and then decompose the molecules themselves. Greenware products break down in approximately 50 days. This technology was awarded the Presidential Green Chemistry Challenge Award in the U.S.A. in 2002. Bioplastics manufacturers claim that their products significantly reduce greenhouse gas emissions by not using petrochemicals as a raw material. PLA production uses 20% to 50% less fossil fuels than the production of traditional plastics. However, fossil fuels supply the energy for the production processes and for industrial composting at the end of the product's life cycle. Taking this into account, the "greenness" of these products is open to debate. ### The Benefits of Bioplastics Other uses of bioplastics include cutlery, food containers, and other types of packaging. While there are many advantages to using bioplastics, there are also arguments against their use. The corn used to provide the raw material is being diverted from the food supply. This raises corn prices and puts pressure on the limited area of agricultural land. It may lead to food shortages in some parts of the world, where farmers can get a higher price for their crops from bioplastics producers than the local population can afford to pay. Some people claim that bioplastics contaminate already established recycling processes. As well, bioplastics are expensive because they are made by emerging technologies. The cost may however, come down as the technologies become established. ## Less Toxic Materials: Flame-Resistant Bioplastics We should all be concerned about the flammability and heat resistance of consumer products. For example, the plastic coating for electrical wires must be flame resistant to reduce the chance of electrical fires (Figure 2). As well, materials that are designed for use with hot objects must not melt, deform, or decompose. For example, a laptop computer case must be able to withstand high temperatures. The material must have relatively strong intermolecular forces. The flame-resistant materials that are typically used in these products are toxic. The electronics industry, for example, uses brominated flame retardants (BFRs) in its plastics. BFRs do not break down easily so they are persistent in the environment. They also enter the food chain (for example, by fish eating contaminated sediment) and bioaccumulate in the tissues of carnivores. Environmental scientists are concerned about the effects of these toxic chemicals on the environment and on human health. Scientists are trying to replace these toxic plastics with bioplastics. PLA alone, however, is quite flammable. What would be a suitable additive, to reduce the flammability? Instead of using BFRs, scientists have developed a "green" alternative. This flame-retardant bioplastic uses a metal hydroxide flame retardant to absorb thermal energy. The energy is then unavailable for breaking intermolecular bonds. Tests show that this significantly improves the bioplastic's ability to withstand heat. NEC scientists have also developed a bioplastic made from a combination of PLA and fibre from a plant called kenaf. This biodegradable "super plastic" is stronger, and has a greater ability to resist heat, than PLA alone. Such a material promises to be very useful in products where heat resistance is required, such as in electronic devices. ## Recycled Materials: Clothing from Pop Bottles How many pop bottles does it take to make a polar fleece jacket? For years, an outdoor goods and gear company called Patagonia has been using recycled PET bottles to make their fleece products. Torontonians alone use about 100 million to 125 million plastic bottles every year. Approximately 50% are recycled. The remaining bottles end up in landfill sites. It takes about 25 pop bottles to make a fleece product. The used bottles are first sorted and cleaned, then heated until they melt. Additional petrochemicals are added to give the material its desired consistency and properties. The liquid is turned into threads by squeezing it through tiny holes in a metal plate. After cooling, these threads go through further steps to turn them into a warm, soft, and durable fabric. ## Figure Descriptions **Figure 1:** A bioplastic cup produced primarily from corn **Figure 2:** The plastic coating on electrical wires must meet strict requirements for flame resistance. **Figure 3:** (a) Plastic bottles at a recycling facility (b) Fleece fibers are produced from molten PET-a type of polyester. (c) Fleece products are especially appropriate in Canada!