Extrusion stretch blow moulding

Fig. 4.25 Extrusion stretch blow moulding Injection Stretch Blow Moulding...

In extrusion stretch blow moulding the first stage is similar to the first stage of extrusion blown, but the parison formed is conditioned to a specific temperature prior to stretching initially by a descending rod and then by compressed air (Figure 7.9). 

Figure 7.9 Extrusion stretch blow moulding (1) extrusion (2) blowing and conditioning (3) stretching (4) blowing (5) ejection...

The main types of NatureWorks PLA that are available for packaging applications include general purpose film grades, extrusion coating, extrusion and thermoforming grades and injection stretch blow moulding. 

Alpha Packaging manufactures botdes and jars made from polyethylene terephthalate (PET) and high-density polyethylene (HDPE) for the pharmaceutical, nutritional and personal care markets. Technologies used include injection blow moulding, injection stretch blow moulding, and extrusion blow moulding. Alpha manufactures stock and custom containers in a variety of styles and colours. 

In an extrusion blow-moulded polyethylene container with a 1 mm wall, about 5 s elapse before crystallisation takes place at the inner surface (Eq. 5.2). During this time, the melt tensile stresses relax, so the microstructure will be spherulitic, even though the spherulites may be somewhat distorted. In contrast there is high orientation in the wall of a stretch blow-moulded PET bottle (Section 2.4.7) because crystallisation occurred while the preform was stretching. 

Blow moulding describes any shaping process in which air is used to stretch and form plastic materials and can be compared to inflating a balloon. A hot thermoplastic tube, usually made by extrusion, can be inflated with compressed gas while inside a cooled split mould. Hot thermoplastic tubes or parisons can also be blown into free shapes without the aid of a mould (Figure 3.33). Plastic bottles, drums, car fuel tanks and other containers are often made using blow moulding (Figure 3.34). 

Lateral stretching during blow moulding and film extrusion emphasises the presence of striations. 

---