Green Chemistry in Action: Choosing the Right Materials PDF

## Green Chemistry in Action: Choosing the Right Materials Green chemistry is relatively new. Understanding the bonding and structure of a compound helps predict its properties and uses. In the past, chemists developed products without considering environmental effects. "Green chemistry" involves i...

## Green Chemistry in Action: Choosing the Right Materials Green chemistry is relatively new. Understanding the bonding and structure of a compound helps predict its properties and uses. In the past, chemists developed products without considering environmental effects. "Green chemistry" involves inventing, designing, and using products and processes that have minimal environmental impact. ### Table 1: Some Aims of Green Chemistry | Aim | Description | |---|---| | Sustainability | Starting with renewable materials rather than nonrenewable sources. | | 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 Companies can develop green alternatives starting with renewable materials. The goal is to create a product that functions efficiently and presents no risks to human health or the environment, including the handling of byproducts. Consider the lifecycle of the product: from manufacturing to disposal. Most plastics are petrochemicals produced from fossil fuels, which are non-biodegradable. Many plastics can be recycled at the end of their product life. Bioplastics are plastics made from chemicals derived from plants. The plastic cup in Figure 1 is manufactured under the name "Greenware." It is made from polylactate (PLA), which is synthesized from corn. Greenware is marketed as "green" because it is compostable. At 55 °C and 90% humidity, micro-organisms break the intermolecular bonds and decompose the molecules themselves. Greenware products breakdown in approximately 50 days. This technology was awarded the Presidential Green Chemistry Challenge Award in the US 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 traditional plastics. However, fossil fuels supply the energy for production processes and industrial composting. 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. Using corn for bioplastics production diverts corn from the food supply. It can 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. Bioplastics are expensive because they are made by emerging technologies. The cost may 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. 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 plastics. BFRs do not break down easily so they are persistent in the environment. They also enter the food chain and bioaccumulate in tissues of carnivores. Environmental scientists are concerned about the effects of these toxic chemicals on the environment and human health. Scientists are trying to replace these toxic plastics with bioplastics. PLA alone, however, is quite flammable. Scientists have developed a "green" alternative flame retardant bioplastic. They use a metal hydroxide flame retardant to absorb thermal energy instead of BFRs. 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 fiber from a plant called kenaf. This biodegradable "super plastic" is stronger and has a greater ability to resist heat than PLA alone. This 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? An outdoor goods and gear company called Patagonia has been using recycled PET bottles to make their fleece products (Figure 3). Approximately 50% of bottles 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.