What is the difference between HDPE, LDPE, LLDPE?

LDPE (Low density polyethylene) : LDPE is a thermoplastic obtained by the free radical polymerization of ethylene under high pressure. It is the earliest member of the polyethylene family and has been commercially produced as a wire wrapper since the early 1940s. Its properties include transparency, chemical inertness, good sealing ability and easy molding processing. Excellent cold resistance, low temperature resistance, not high temperature resistance. Due to its branch structure, it has excellent transparency, flexibility and easy extrusion properties.

LDPE applications include food packaging, fiber product packaging, daily chemical packaging and pharmaceutical packaging, etc., can also be used as a thermal sealing layer of composite flexible packaging materials. For example, pickle can be designed as BOPP/VMPET/LDPE structure, wherein LDPE is used as non-toxic and odorless heat sealing material.

HDPE (high-density polyethylene) : HDPE is a white powder or granular product, non-toxic, tasteless, crystallinity of 80% to 90%, softening point of 125 to 135 ° C, the use of temperature up to 100 ° C. Compared with LDPE, HDPE has better hardness, tensile strength and creep, wear resistance, electrical insulation, toughness and cold resistance. The extensibility of the film is small, and the tensile strength and impact resistance are large. Good heat resistance, and can also show better strength at low temperatures. It has good chemical stability, insoluble in any organic solvent, and resistant to acid, alkali and various salts. The film has little permeability to water vapor and air, and low water absorption.

It is mainly used for moisture-proof bags, convenient bags (vest bags) garbage bags, and its co-extruded film is also used to make dairy products and frozen food packaging. For example, the frozen food packaging material is HDPE/EVA, which takes advantage of non-toxic and tasteless, excellent high and low temperature resistance and low price.

LLDPE (Linear Low Density Polyethylene) : LLDPE has the molecular structure of a very short copolymer monomer branch chain. Its production starts with transition metal catalysts, especially of the Ziegler or Philips type. Compared with LDPE, LLDPE has a narrower molecular weight distribution and a smaller shear sensitivity. Has good tensile strength and impact strength, soft and toughness, oil resistance, chemical resistance is better than LDPE. The thermal adhesion is very good, and the thermal sealing strength has little relationship with the thermal sealing temperature, and the thermal sealing temperature range is wide and the strength is high.

Its processing properties are similar to LDPE and it has excellent rheology or melt fluidity.

LLDPE can be made into garbage bags, ice bags, grocery bags, heavy bags and winding bags, etc., can also be used for the inner sealing layer of composite flexible packaging materials, compared with LDPE to make bags reliable, the heat sealing strength at the seal is higher but the cost is higher than LDPE. For example, the packaging material structure of liquid cleaners :BOPA/LLDPE, LLDPE as an inner sealing material, good resistance to sealing pollution.