Meaning
Synthetic thermoplastic polymers synthesized through transition metal catalysis yield short side branches along a main hydrocarbon chain to provide tear strength and puncture resistance. Within flexible packaging production, linear low density polyethylene provides tensile flexibility without the long-chain branching typical of high-pressure resins. Material classification governs film gauge reduction and seal integrity across commercial converting lines.
Physical scope covers ethylene copolymers produced with alpha-olefin comonomers, ending where high-density rigid formulations begin.
Rheological Behavior
Polymer melt flow exhibits strong extensional viscosity while lacking the strain hardening characteristics of traditional branched polymers. During high-speed extrusion, linear low density polyethylene requires higher motor torque and elevated die pressures compared to low density resins of equivalent melt index. Laboratory capillary rheometer data showing narrow molecular weight distribution often understate melt fracture tendencies on production scale dies.
Melt fracture creates surface haze and reduces clarity, forcing extruders to incorporate fluoroelastomer processing aids or modify die land geometry.
Processing Limitation
Machine power constraints frequently limit the processing speed of unmodified polymer grades on older extrusion equipment. Blending linear low density polyethylene with low density resin improves melt strength during bubble formation.
Density Specification
Density measurements range strictly between zero point nine one five and zero point nine three zero grams per cubic centimetre. Values above this boundary alter crystal structure, shifting classification into medium density polymers.
