Families Of Plastics

There are two basic families of plastics: Thermoplastic materials and Thermoset materials.

Thermoplastics soften and melt upon the addition of heat. Upon removal

of heat they then again stiffen and harden into a new shape. The Thermoplastic family is what most people relate to when they think about plastics because of the many domestic products that are produced from them. What red blooded American male does not have first hand experience with this family of plastics when as a child built Revelle models of boats, cars or other objects and then lit them on fire only to end up with an amorphous blob?

The injection molding technique was developed to efficiently process this family of plastics into the many useful products we use everyday. Some of the commonly used thermoplastics are polyethylene, polypropylene, polystyrene, PVC, ABS and Nylon to name a few. There are countless other engineered plastic materials and compounds to suit broad varieties of applications. Southwest Plastics has extensive injection molding capabilities for thermoplastic materials.

Thermosets harden and cure in the molding process as the molecules actually crosslink in a chemical reaction and set into a final shape. No addition of heat will soften or melt the material. As a result, thermosets have their advantage in any high heat environment where softening or melting cannot be tolerated. Domestically products such as ash trays, cooking utensils and cookware handles are produced from thermosets. Industrially thermosets are used in electrical, electronic and military applications. Some examples of thermoset materials are phenolics, epoxys, melamines and diallylphthalates.

Thermosets can be molded using the compression, transfer or injection molding processes. Southwest Plastics has extensive capabilities in molding thermoset materials using all three of these processes.

Source : www.southwestplastics.com/learn-more/a-brief-history-of-plastic-injection-molding-process

Recycling Of Plastic

The Society of the Plastics Industry (SPI) established a classification system in 1988 to allow consumers and recyclers to identify different types of plastic. Manufacturers place an SPI code, or number, on each plastic product, usually moulded into the bottom. This guide provides a basic outline of the different plastic types associated with each code number.

Polyethylene Terephthalate sometimes absorbs odours and flavours from foods and drinks that are stored in them. Items made from this plastic are commonly recycled. PET(E) plastic is used to make many common household items like beverage bottles, medicine jars, rope, clothing and carpet fibre.

High-Density Polyethylene products are very safe and are not known to transmit any chemicals into foods or drinks. HDPE products are commonly recycled. Items made from this plastic include containers for milk, motor oil, shampoos and conditioners, soap bottles, detergents, and bleaches. It is NEVER safe to reuse an HDPE bottle as a food or drink container if it didn’t originally contain food or drink.

Polyvinyl Chloride is sometimes recycled. PVC is used for all kinds of pipes and tiles, but is most commonly found in plumbing pipes. This kind of plastic should not come in contact with food items as it can be harmful if ngested.

Low-Density Polyethylene is sometimes recycled. It is a very healthy plastic that tends to be both durable and flexible. Items such as cling-film, sandwich bags, squeezable bottles, and plastic grocery bags are made from LDPE.

Polypropylene is occasionally recycled. PP is strong and can usually withstand higher temperatures. It is used to make lunch boxes, margarine containers, yogurt pots, syrup bottles, prescription bottles. Plastic bottle caps are often made from PP. Polystyrene is commonly recycled, but is difficult to do. Items such as disposable coffee cups, plastic food boxes, plastic cutlery and packing foam are made from PS.

Code 7 is used to designate miscellaneous types of plastic not defined by the other six codes. Polycarbonate and Polylactide are included in this category. These types of plastics are difficult to recycle. Polycarbonate (PC) is used in baby bottles, compact discs, and medical storage containers.

Source : www.ryedale.gov.uk/pdf/Different_plastics.pdf