Development Polyethylene (Polythene) is one of the world’s most popular plastics. It is an enormously versatile polymer which is suited to a wide range of applications from heavy-duty damp proof membrane for new buildings to light, flexible bags and films. There are two major types of PE are in use in the films and flexible packaging sector, which are as follows:- HDPE ( High Density) - Used for most thin gauge carrier bags, fresh produce bags and some bottles and caps LDPE- (Low Density) -Used generally for trays and heavier duty film such as long-life bags and sacks, poly tunnels, protective sheeting, food bags etc
Low-density polyethylene Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerization. Its manufacture employs the same method today. The EPA estimates 5.7% of LDPE (recycling number 4) is recycled. Despite competition from more modern polymers, LDPE continues to be an important plastic grade. In 2013 the worldwide LDPE market reached a volume of about US$33 billion. Properties LDPE is defined by a density range of 0.910–0.940 g/cm3. It is not reactive at room temperatures, except by strong oxidizing agents, and some solvents cause swelling. It can withstand temperatures of 80 °C continuously and 95 °C for a short time. Made in translucent or opaque variations, it is quite flexible and tough. LDPE has more branching (on about 2% of the carbon atoms) than HDPE, so its intermolecular forces (instantaneous-dipole induced-dipole attraction) are weaker, its tensile strength is lower, and its resilience is higher. Also, because its molecules are less tightly packed and less crystalline due to the side branches, its density is lower.
CHEMICAL RESISTANCE Excellent resistance (no attack / no chemical reaction) to dilute and concentrated acids, alcohols, bases and esters Good resistance (minor attack / very low chemical reactivity) to aldehydes, ketones and vegetable oils Limited resistance (moderate attack / significant chemical reaction, suitable for short-term use only) to aliphatic and aromatic hydrocarbons, mineral oils, and oxidizing agents Poor resistance, and not recommended for use with halogenated hydrocarbons.
Applications A piece of packaging foam made from LDPE LDPE is widely used for manufacturing various containers, dispensing bottles, wash bottles, tubing, plastic bags for computer components, and various moldedlaboratory equipment. Its most common use is in plastic bags. Other products made from it include: Trays and general purpose containers Corrosion-resistant work surfaces Parts that need to be weldable and machinable Parts that require flexibility, for which it serves very well Very soft and pliable parts such as snap-on lids Six pack rings Juice and milk cartons are made of liquid packaging board, a laminate ofpaperboard and LDPE (as the waterproof inner and outer layer), and often with of a layer of aluminum foil (thus becoming aseptic packaging). Packaging for computer hardware, such as hard disk drives, screen cards, andoptical disc drives Playground slides Plastic wrapsPHYSICAL PROPERTIES
ADVANTAGES: Low cost Impact resistant from -40 C to 90 C Moisture resistance Good chemical resistance Food grades available Readily processed by all thermoplastic methods DISADVANTAGES AND LIMITATIONS: High thermal expansion Poor weathering resistance Subject to stress cracking Difficult to bond Flammable Poor temperature capability