Polypropylene blow moulding

As a blow moulding material polypropylene has never enjoyed the success of HDPE. This is in large measure because moulding of the former requires more attention to equipment design and operating conditions. Many successful mouldings have nevertheless been made commercially including chairs, horticultural sprayers and motor car parts. 

Substantial quantities of UPVC are also used for blow moulded containers for such diverse materials as consumable liquids such as fruit squashes, liquids for household use such as detergents and disinfectants, cosmetics and toiletries, and pharmaceuticals. For most of these applications UPVC is in competition with at least one other polymer, particularly poly(ethylene) terephthalate (Chapter 25), polyethylene (Chapter 10), polypropylene (Chapter 11) and, to a small extent, the nitrile resins (Chapter 15). The net result is that in recent years there has been some replacement of PPVC in these areas, in part because of problems of waste disposal. 

During the blow moulding of polypropylene bottles, the parison is extruded at a temperature of 230°C and the mould temperature is 50°C. If the wall thickness of the bottle is I mm and the bottles can be ejected at a temperature of I20°C estimate the cooling time in the mould. 

Among the plastics suitable for blow moulding are polyethylenes, polypropylenes, polyacrylonitrile, thermoplastic polyesters, polycarbonates... 

In the method of producing a hollow foamed plastic body from polyethylene or polypropylene by means of an extrusion blow-moulding process using a single-screw... 

Polypropylene (PP) bottles have the advantage that they are inherently hot-fillable (at 85°C) and retortable to 120°C. The bottles are normally extrusion blow-moulded, and can also be made with multi-layering to include barriers against oxygen permeability. This technology is commonly used for sauce bottles and juice products. Since most of the bottles are of an oval shape, product contraction resulting in volume reduction is countered by allowing die bottle to become more oval under the effects of vacuum. 

Thermoplastics consist of long chains of molecules, in the case of PE these are unbranched. Many of these chains together form a tangle which is more difficult to unravel the more branched the chains are. The branches are like hooks which cause the molecules to catch. Under the influence of relatively small external forces chains and parts of chains can slide across each other. PE is for instance used to make containers, chemical tubing and blow-moulded bottles. Some other thermoplastics are polypropylene (crates), polyvinyl chloride PVC (pipes) and polystyrene (foam). 

Bomatic, Inc. has been a producer of plastic bottles and containers since 1969. The company serves the personal care, automotive, pharmaceutical, medical, lawn and garden, food, household cleaners, and industrial chemicals markets. Production capabilities include extrusion blow moulding and injection moulding products made from HDPE, PVC, LDPE, PET, PETG, polycarbonate, polystyrene, polypropylene, and polyurethane. 

Biodegradable polymers are similar in terms of their chemical structure to conventional thermoplastics such as polyethylene, polypropylene and polystyrene. They can be processed using standard polymer processing methods such as film extrusion, injection moulding and blow moulding. 

Melt degradation is used commercially to narrow the molecular weight distribution, from a starting value of Mw/Mn = 5, to make it more suitable for fibre spinning and blow moulding. Random chain scission at tertiary C—H bonds eventually produces a most probable molecular weight distribution with M /Mn = 2. In practice, the distribution, produced by deliberately degrading the polypropylene with added peroxides, is broader, but... 

Whether an additive is used in concentrated masterbatch form or in its standard form will vary depending on the requirements of particular producers. Masterbatches are routinely used for blow moulding and film blowing in commodity plastics such as polypropylene (PP), LDPE and high-density polyethylene (HOPE). 

Excellent resistance to mechanical fatigue gives PP its unique hinge property. A service temperature of 120°C allows sterilisation. Polypropylene is available in granules or powder and as sheet in natural (off-white) translucent to opaque colours. It is processable by injection and blow moulding and the sheet can be formed by all techniques in use. PP is also produced in monofilaments and fibres. 

Blow moulding produces fairly good surface finish as for many items there is no further surface finishing necessary. Familiar products manufactured by blow moulding include drinks bottles, shampoo bottles, water dmms and plastic barrels. The plastics that are used in blow moulding include low density polyethylene (LDPE), high density polyethylene (HDPE) and polypropylene (PP). 

One unfortunate characteristic property of polypropylene is the dominating transition point which occurs at about 0°C with the result that the polymer becomes brittle as this temperature is approached. Even at room temperature the impact strength of some grades leaves something to be desired. Products of improved strength and lower brittle points may be obtained by block copolymerisation of propylene with small amounts (4-15%) of ethylene. Such materials are widely used (known variously as polyallomers or just as propylene copolymers) and are often preferred to the homopolymer in injection moulding and bottle blowing applications. 

Blow-fill technology is an aseptic process whereby the container is formed from thermoplastic granules, filled with sterile solution and sealed, all within one automatic operation. The bulk solution should have a low bioburden and is delivered to the machine through a filling system that has been previously sanitized and steam sterilized in situ. Concern has been expressed that the machine itself may generate particles. The plastic granules are composed usually of polyethylene, polypropylene or one of their copolymers and are heat extruded at 200°C into a tube. The two halves of a mould close around this tube and seal the base. The required quantity of sterile fluid is filled into the container, which is then sealed. Products packed in this way include intravenous solutions, and small volume parenteral, ophthalmic and nebulizer solutions. The... 

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