PP resins can be processed by a number of techniques such as PP Bottle(KEXON), which has been around for several decades; injection blow moulding (IBM), which is mainly suited for smaller size containers (normally used in the pharmaceutical and cosmetic industries); and injection stretch blow moulding (ISBM).

In the one-step ISBM process, the PET resin is converted into containers in one machine, whereas the two-step process includes first making a preform by injection moulding and then reheat-stretch-blow moulding it into containers on a second machine.

The ISBM process offers a number of advantages over EBM. The ISBM process provides excellent clarity and outstanding neck finish, as the neck of the container is injection-moulded. This is very important to protect the aroma and flavour of the product inside the package. The ISBM process also offers superior impact strength, as there is no pinch-off at the bottom of the container as in the EBM process.

Moreover, the ISBM process provides greater rigidity due to biaxial orientation of chain molecules. It is also a scrap-free process. ISBM containers have better gloss and surface finish than EBM containers.

The main reason for not using PP in the ISBM process is that the advantages of lower resin cost and lower density are offset by the higher conversion cost of PP compared to PET. This is because the thermal conductivity of PP is poorer, which contributes to lower throughput for PP in the ISBM process – as much as 20-30 per cent lower for standard PP compared to PET.

Moreover, the gas barrier properties of PP are about 30 times poorer than those of PET. A number of food packaging applications require the oxygen barrier in PP to be similar to that of PET. If the barrier materials manufacturers could develop a gas barrier material for PP, the opportunities are enormous.

This could be achieved using a number of different methods, such as multilayers, coatings, scavengers and nanocomposites. The key to success, however, is to develop a barrier technology that is cost-effective.

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