High-density polyethylene impact strength

The homopolymer finds a variety of uses, as an adhesive component, as a base for chewing gum, in caulking compounds, as a tackifier for greases, in tank linings, as a motor oil additive to provide suitable viscosity characteristics and to improve the environmental stress-cracking resistance of polyethylene. It has been incorporated in quantities of up to 30% in high-density polyethylene to improve the impact strength of heavy duty sacks. 

The radius of the notch is quite important, particularly for plastics. For example, polyvinyl chloride (PVC) is a notch-sensitive material. If the notch is blunt (2-mm radius), the impact strength is higher than that for ABS. If the notch is sharp (0.25-mm radius), the impact strength of PVC is lower than that for ABS. Other polymers that are notch brittle are high-density polyethylene (HDPE), polypropylene (PP), polyethylene teraphthalate (PET), dry polyamides (PAs), and acetals. 

Figure 2. Impact strength (high-density polyethylene. 08-in. injection-molded 0.3% LS 45° south...

Polyallomers combine the most desirable properties of both crystalline polypropylene and high-density polyethylene (HDPE) and can offer impact strengths three or four times that of polypropylene. Resistance to heat distortion is better than that of HDPE but not quite as good as that of polypropylene. Polyallomer has better abrasion resistance than polypropylene and comparable hingeforming characteristics. 

High-density polyethylene (HDPE)/ultra-high molecular weight polyethylene (UHMWPE) blends are possible by direct compounding, and use of UHMWPE could improve the impact strength or tensile strain of HDPE. The effect of the UHMWPE content on the mechanical properties of the HDPE/UHMWPE blends is improved by compounding due to homogenisation of the mixture [35-39]. 

High-density polyethylene, HDPE, was blended with 50 wt% polypropylene, PP, having matched melt flow index, to give good flowability, weld-line strength, surface quality, and low-temperature impact strength... 

Figure 18.37 Falling weight impact strength of high density polyethylene at 23 °C).

Figure 18.42 Effect of temperature on falling weight impact strength of 0.080 inch thick injection moulded specimens of various polymers moulded at 240 °C. KMT 61 and GMT 61 = polypropylene copolymers, 65-045 = high-density polyethylene, GM 61 and KM 61 = polypropylene homopolymer, ABS = acrylonitrile-butadiene-styrene terpolymer. Source Author s own files)...

Figure 18.46 Effect of melt index on falling weight impact strength of various high-density polyethylenes at 23 °C (1.5 mm compression moulded samples).

FIGURE 2.15 Influence of temperature on Izod impact strength of various polymers of low and high melt indexes. GMT 61 is a low-melt-index and low-notch-sensitivity polypropylene copolymer. KMT 61 is a high-melt-index and low-notch-sensitivity polypropylene polymer. HDPE 65045 is a high-melt-index and high-notch-sensitivity high-density polyethylene. 

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