Monday, April 25, 2011

Second life for plastics

All thanks to Discovery Science Channel, I learnt quite a lot these few days. One of them that I find it great is the second life of plastics as featured in the program called Eco-Life.

Plastic bottle making

As everyone knows, plastics is inevitable around us and in the material science that we studys every plastics are vulnerable to chemicals, temperature and toxicity. However, there are people still using plastic because ironically, industrial prefers plastic because of low energy cost, easy access to material and high productivity manufacturing as compared to other materials. It is although recyclable but in each lot, only 30% of recyclable plastics is allowed due to instability of the atomic strucure and properties.

In the show, it describes something that we have never noticed before in every plastic bottles. That is the SPI(Society of Plastic Industry) Resin Identification Code as specified in some labels or even on the body of the plastic bottle. This is denotes by three enclosing arrows with a number 1 or 2 in the center.

PET stands for Polyethylene Terephthalate. It is a thermoplastc polymer resin of the polyester family and is used in most plastic containers be it food, liquid and thermoforming applications.

There are 7 Resin Idenfication Code(RIC) and most commonly used are Code 1 and 2, which is commonly recycled because of its ease in forming and low heating requirement. however because of the low heaing properties, common drinking bottles are not recommended for hot water application especially to boiling water. Class 3 to class 7 are harder plastics and they can withstand higher heat.

According to Science Channel, one man who have concern on the plastic uses come out with an ingenious plan of mixing plastics. As fr as recycling is concern, plastics are best not to mix because of their different chemical structure. What he did is by engineering modification, he have managed to come up with a process that mix class 2 and class 5 plastics and bond them together with a special extrusion process that he has patented and the product becomes a construction material with strength high than steel itself. It can be used to construct bridges and these two class of plastic materials have their own advantages and disadvantages. For example class two has high ductility but low yield strength and low resistance to heat and chemical. whereas class 5 plastic has high yield strength, high resist to chemicals, heat and toughness but it is brittle. So in the special process it bond the two class of plastics together and create a new material suitable for construction in the form of I beam. So with the revolution of the plastics, metals expecially iron can be replaced wih plastics because of its high resistance to corrosion as what nature does.

Problem with plastics in drinking water bottle

In Engineering Material Science, every plastics has a temperature called glass temperature. This is the temperature where plastics is heated to a temperature to a point where it exist in both solid and liquified state. Suppose if a water it contains reached this temperature, polyester can leak into the water and create toxic if consumed. One of the commonly famous plastic toxic is Bisphenol commonly known as BPA. It is an important component of plastic water bottles, baby bottles, inner lining of food cans, microwave containers, and hundreds of common household and industrial products. The use of BPA-containing plastic in the packaging of food and beverages is alarming because there is a long list of health disorders attributed to the chemical.

If heated water is required for transportation, it is best to use bottles made of stainless steel even though studies have shown that the optimum container is glass bottles. Glass bottles can experience sudden explosion in the case of Vaccuum bottles. It breaks easily and non-recyclable. So if water container is required, use glass cup and be sure to hold the handle. If traveling around is required, use a double walled stainless steel bottle. Having no glass temperature as what plastic experiences, both glass and stainles steel melting point is at 1510 degree Celcius. This is 15 times more than boiling water temperature. Even if the water is superheated, it can reached to a maximum of 250 degree celcius which the stainless steel can holds. That is why stainless steel double walled insulated is best recommended for holding a hot water or cold water.

Although BPA is only lethal at very high doses, increasing scientific evidence suggests that it can disrupt key body functions at very low doses, and builds up in our bodies over time with each exposure. Despite the multiple scientific studies that clearly link BPA to developmental and other abnormalities in animals and humans, the US Food and Drug Administration (FDA) issued a statement on August 15, 2008 reaffirming the safety of products containing low levels of BPA. However, no mention is made of the effects of repeated exposure over many years, or of the effect of combinations of hormones and BPA.

There are billions of people around the world who drink water from plastic bottles every day. Unfortunately, bottled water is harmful to the environment, your wallet and your health. Ironically, people who buy bottled water in an effort to improve overall well-being are actually putting their health at risk. BPA and other toxic chemicals have been shown to leach out of both single-use and reusable plastic water bottles. Repeated use of plastic bottles has been shown to increase the rate of chemicals like BPA leaching out, especially bottles intended for single use.

Extract from


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