There are two main types of plastics
which are softened by heat and can be moulded. (Injection moulded, blow moulded or vacuum formed). Good examples are acrylic, polypropylene, polystyrene, polythene and PVC.
which are formed by ha heat process but are then set (like concrete) and cannot change shape by reheating. Good examples are melamine (kitchen worktops), Bakelite (black saucepan handles), polyester and epoxy resins.
Composites are made by mixing materials together to get enhanced properties. Polyester resin is mixed with glass fibre to make GRP used for boatbuilding and fishing rods. Epoxy resin plus carbon fibre is stronger than steel but lighter.
How to choose plastic resins?
When beginning the process of developing a plastic component through the injection molding process, one of the top priorities needs to be identifying the type or types of resin to be used on the product. While there is opportunity to customize the resins to fit the end use of the part, there are a wide variety of resins available, which opens up unlimited possibilities in design and function.
The first step in the process is to identify the key physical attributes that the end product requires. Below is a list of properties the need to be evaluated:
Chemical and environmental resistance
Temperature operating range
Next, you will need to choose from a wide variety types of resins. With these resin classes you have a variety of products that gives you flexibility to customize your needs. It also allows you to match the resin to the part design and mold ability of the part.
Engineering Grade Resins
||Tough, good thermal and chemical resistance, with a wide variety of grades available with broad scope of physical properties.
||Strong, high flex modulus, good temperature range, transparent.
||Good impact, superior surface quality, good color-ability, good rigidity, with electroplatable grades available.
||Good processability, good toughness at low temperature, good dimensional stability.
||“Soft” touch materials, rubber replacement materials, good tear strength, and good flexibility.
||High optical clarity, good lens materials
||Excellent wear resistance, excellent material for gears and high wear applications.
||Excellent material to be used in where metal replacement is applicable. Good weight-to-stiffness ratio.
||Versatile material, variety of grades in homopolymer and copolymer classes, good chemical resistance, good fatigue resistance, excellent chemical resistance, lower cost.
||Very versatile, low-cost material, variety of grades in LLDPE, LDPE, and HDPE, tough, weatherable, and easily processed.
||Available in general purpose PS and HIP polystyrene, lower cost, range of impact from low to high, good clarity in GPPS grades, good rigidity.
How many types of plastics there are?
There is no exact number. It’s sort of like asking how many types of bread there are. Plastics aren’t simply one material made the same way every time. Although plastics can be broken down into broad types or categories, there actually are thousands of different plastics, each with its own composition and characteristics. One plastic may block oxygen from reaching food. Another may be transparent like glass yet tough. Or stretch and bounce back in shape. Another may trap air inside itself. Or stop a bullet.
That’s why plastics are used in so many ways: they protect our food, cushion our fall, insulate our homes, improve our cars’ gas mileage, keep us dry when it’s raining… and many other things.
Plastics are a result of a mix of chemistry and engineering. As innovation marches on, scientists and engineers can create new plastics to do more and more things.
So even though the number of plastics is unclear, plastics makers tend to group plastics into two general classes: thermoplastics and thermosets.
Thermoplastics can be re-melted and essentially returned to their original state—sort of like the way an ice cube can be melted and then cooled again. Thermoplastics usually are produced first in a separate process to create small pellets; these pellets then are heated and formed to make all sorts of consumer and industrial products. Thermoplastics include plastics you’re likely familiar with: polyethylene, polypropylene, polyvinyl chloride, polystyrene, nylon, polycarbonate, and others.
Thermosets are usually produced and formed into products at the same time—and they cannot be returned to their original state. They generally are formed using heat (“thermo”) and become “set,” like a cooked egg. Thermosets include vulcanized synthetic rubber, acrylics, polyurethanes, melamine, silicone, epoxies, and others.
Plastic Classification system
Plastic is an essential component of numerous consumer products, including water bottles and product containers. However, not every kind of plastic is the same. In 1988, the Society of the Plastics Industry (SPI) established a classification system to help consumers and recyclers properly recycle and dispose of each different type based on its chemical makeup. Today, manufacturers follow a coding system and place a number, or SPI code, on each plastic product, usually molded into the bottom. Although you should always verify the plastic classification number of each product you use, especially if you plan on recycling it, this guide provides a basic outline of the different plastic types associated with each code number.
SPI Code 1 PETE/PET
Plastic marked with an SPI code of 1 is made with polyethylene terephthalate, which is also known as PETE or PET. PETE-based containers sometimes absorb odors and flavors from foods and drinks that are stored inside of them. Items made from this plastic are commonly recycled. PETE plastic is used to make many common household items like beverage bottles, medicine jars, peanut butter jars, combs, bean bags, and rope. Recycled PETE is used to make tote bags, carpet, fiberfill material in winter clothing, and more.
SPI Code 2 HDPE
The SPI code of 2 identifies plastic made with high-density polyethylene, or HDPE. HDPE products are very safe and are not known to leach any chemicals into foods or drinks. Plastic Milk Jugs (However, due to the risk of contamination from previously held substances, please note: it is NEVER safe to reuse an HDPE bottle as a food or drink container if it didn’t originally contain food or drink!) HDPE products are commonly recycled. Items made from this plastic include containers for milk, motor oil, shampoos and conditioners, soap bottles, detergents, and bleaches. Many personalized toys are made from this plastic as well. Recycled HDPE is used to make plastic crates, plastic lumber, fencing, and more.
SPI Code 3 PVC
Plastic labeled with an SPI code of 3 is made with polyvinyl chloride, or PVC. PVC is not often recycled and can be harmful if ingested. PVC is used for all kinds of pipes and tiles, but it’s most commonly found in plumbing pipes. This kind of plastic should not come in contact with food items. Recycled PVC is used to make flooring, mobile home skirting, and other industrial-grade items.
SPI Code 4 LDPE
Plastic marked with an SPI code of 4 is made with low-density polyethylene, or LDPE. LDPE is not commonly recycled, but it is recyclable in certain areas. It tends to be both durable and flexible. It also is not known to release harmful chemicals into objects in contact with it, making it a safe choice for food storage. Plastic cling wrap, sandwich bags, squeezable bottles, and plastic grocery bags all are made from LDPE. Recycled LDPE is used to make garbage cans, lumber, furniture, and many other products seen in and around the house.
SPI Code 5 PP
Consumers will find the SPI code of 5 on plastic items made with polypropylene, or PP. PP can be recycled but is not accepted for recycling as commonly as PETE or HDPE. Plastic Stadium Cups This type of plastic is strong and can usually withstand higher temperatures. Among many other products, it is used to make plastic diapers, Tupperware, margarine containers, yogurt boxes, syrup bottles, prescription bottles, and some stadium cups. Plastic bottle caps often are made from PP as well. Recycled PP is used to make ice scrapers, rakes, battery cables, and similar items that need to be durable.
SPI Code 6 PS
Plastic marked with an SPI code of 6 is made with polystyrene, also known as PS and most commonly known as Styrofoam. PS can be recycled, but not efficiently; recycling it takes a lot of energy, which means that few places accept it. Disposable coffee cups, plastic food boxes, plastic cutlery, packing foam, and packing peanuts are made from PS. Recycled PS is used to make many different kinds of products, including insulation, license plate frames, and rulers.
SPI Code 7 Other Plastic Material
The SPI code of 7 is used to designate miscellaneous types of plastic that are not defined by the other six codes. Polycarbonate and polylactide are included in this category. Plastic CDs and DVDs These types of plastics are difficult to recycle. Polycarbonate, or PC, is used in baby bottles, large water bottles (multiple-gallon capacity), compact discs, and medical storage containers. Recycled plastics in this category are used to make plastic lumber, among other products.