Polyolefins PE, PP and blends

1 Polyethylene (PE). Polymethylene, (CH2) , was originally discovered in 1898 (von Pechmann) as a white flocculant solid formed by decomposing diazomethane 

There are three main grades of PE—LDPE, high-density PE (HDPE) and linear low-density PE (LLDPE). 

LDPE is made at pressures of 1000-3000 atm and temperatures of 200-275 Under these conditions ethylene is a supercritical fluid. At the higher temperature ranges, the polymer is dissolved in the ethylene phase, whereas at lower temperatures, the PE separates as a liquid. 

The polymerization takes place via a free radical mechanism and is initiated by peroxides, e.g. benzoyl peroxide and/or O2. The steps are  

3 Properties of PE and PP. The principal feature which determines the properties of PE is the percentage crystallinity—this is the main difference between HDPE (75-85%) and LDPE (50-60%)—MW and MWD. 

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