Half-life HDPE

FIGURE 17.5 Half-life time (time to 50% retained elongation) of different HDPE plaques (2 mm thick) showing synergism of HALS (LMW-HALS-1) and UVA (UVA-BZT-1) (total amount UVA + HALS — 0.2 wt%) [124]. 

Gaylord et al. " reported that the in situ polymerization of MAH in the presence of molten PE, using conditions which initiated the heterogeneous or bulk polymerization of MAH, i.e. catalysts used at high concentrations and at temperatures where the half-life is short, e.g. t-butyl perbenzoate at 150 C, resulted in the grafting of poly-MAH on the PE. Graft copolymerization of MAH onto HDPE has been carried out in an extruder at 190-250 u in the presence of BPO and at 260 C in the presence of t-butyl hydroperoxide. ... 

The most common special feature of the mold is the quick change volume control insert. Rigid volume control is necessary for certain products, such as dairy containers. Here HDPE is used (for many excellent reasons), and the container slowly shrinks and changes in size for many hours after molding. Because of production volume control requirements, some dairies must fill containers molded half an hour before fill and then switch to filling containers molded several days previously. Volume-control inserts that displace the difference in volume between the two types are added to the mold, usually as a disc in the side wall, to ensure that the volume and fill levels are the same in both containers at the time of filling. The device works because HDPE shrinkage is reduced virtually to zero for the life of the container when filled with milk or juice and stored at cold temperatures. 

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