Density grade classification

Physical and mechanical properties differ in density and molecular weight. The three main classifications of density are low, medium, and high. These specific gravity ranges are 0.91-0.925, 0.925-0.940, and 0.940-0.965. These grades are sometimes referred to as Type I, II, and III. 

A special grade meets the demand for halogen-free materials for pultruslon, resin transfer moulding, filament winding, and hand lay-up processes, giving highly retarded composites at a comparatively low addition rate. With this additive, at approximately 50 parts per hundred resin (phr), the Epiradiateur NF 92-501 test - one of the most stringent in Europe - can be passed with a classification of Ml, where 250 phr is required with aluminium hydroxide. With epoxy resins, the same low smoke density is produced as with polyester laminates, at addition levels of 20-50 phr. The aviation standard FAR 25.8 53 can be passed with an addition of 25-35 phr. A liquid-form additive is available where no powder additive can be used. 

No formal classification system is available. However, many different grades of ara-mid fibers are rated by their density (g/cm ), percent elongation, modulus (GPa), and tenacity (breaking strength/denier). 

Figure 2.1 Classification of PE grades. HDPE High-density PE, MDPE Medium-density PE, LDPE Low-density PE, LLDPE Linear low-density PE, ULDPE Ultra low-density PE, VLDPE Very low-density...

The density of PE depends on the polymerisation process used and on the thermal history of each sample (Figure 2.1 and Table 3.2). It markedly influences the properties and represents the main property used in the classification of PE grades (see previously). The density of a 100% crystalline sample is considered as 1 g/cm, while that of a 100% amorphous sample is 0.85 g/cm ... 

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