Blown extruded film

Confocal laser scarming mieroseopy has been used to study three-dimensional distribution of siliea partieles in blown extruded film. The results show that very few particles are present on the surface, and these few whieh are found on the surfaee eome from undispersed agglomerates. These results show that a microroughness mechanism should be reeonsidered. It should be assumed that materials whieh require antibloeking are thermoplastie and their matrix pol nner eannot be completely isolated on the surfaee by 2,000 ppm addition of filler that will prevent moleeules of polymer from two films in eontaet to penetrate eaeh other if they have sufficiently mobile eomponents. 

Since starch is biodegradable, it has found use as filler in polymers, such as extruded films applied to paperboard for use in packaging.295,296 The starch is incorporated in granular form,297 as an octenylsuccinate derivative298 and in other forms. Starch-based blown films are prepared from starch-poly(ethylene-co-acrylic acid) formulations.299... 

Thin cast, blown, or extruded films may require extremely small particle size pigments that will not cause tears in the film. 

Typically, the expansion ratio between die and blown tube of film would be 1.5 to 4 times the die diameter. The drawdown between the melt wall thickness and the cooled film thickness occurs in both radial and longitudinal directions and is easily controlled by changing the volume of air inside the bubble and by altering the haul off speed. This gives blown film a better balance of properties than traditional cast or extruded film, which is drawn down along the extrusion direction only. 

Most blown film operations extrude the resin in an upward direction. However, blown polypropylene film is generally extruded downwards and water or mandrel quenched. The extruded tube is then reheated, to a point still below its melt temperature, before it is blown. The collapsed bubble can be fed over a series of heated rollers to reheat it and relieve thermal stresses if a heat-stabilized film is wanted or it can be heated and reinflated in what is known as the double bubble process, which will be discussed in Section 7.3.7. In either case, the film is restrained until cooling is complete, to keep it from shrinking. 

Bu Informal abbreviation for bytyl. bubble 1. A void, or globule of gas or air, trapped in a plastic product, usually as a result of faulty processing. See air entrapment. 2. In extruded blown (tubular) film production, the tube extending from the die to the nip roll. See extruded blown film. 

This chapter covers many of the most important properties measured by producers of blown film. These include mechanical, thermal, optical, physical, electrical, and rheological. The first five in this list apply primarily to the extruded film and the last one applies to the molten polymer inside the extruder and die. By obtaining the measurement values for these properties, manufacturers gain assurance that their resin or film will perform adequately, whether during manufacture (extrusion or conversion) or in final product form as used by the customer. 

PLA is a semicrystaUine plastic that can be injection molded, extruded or blown into film, spun into fibers, blow molded, extruded, and expansion molded. The somewhat lower thermal stability and impact strength (Lim et al., 2008) as well as the moderate oxygen/water permeability (van Tuil et al., 2000) may limit its use in some applications despite its low cost (Lunt, 1998). Compostability of PLA is emphasized in marketing PLA products even though the product is compostable, it does not readily biodegrade under ambient conditions or under anaerobic conditions (Integrated Waste Management Board, 2007) (see also Chapter 6). 

A typical blown film extrusion device is shown in Figure 1.7. The molten polymer from the extruder enters the die and is forced around a mandrel and emerges from a ring shaped die. The extruded film tube is then expanded to a specific diameter by air pressure from the center of the mandrel. As the bubble expands, film thickness decreases. The "frost line" shown in Figure 1.7 is the line where solidification of the extrudate commences. 

A different aspect of the volatile emissions and odom problem arose recently in North America when processors asked Akcros America to develop barium-zinc stabilisers for use in PVC garment bags and reusable packaging made from calendered or extruded film. These are products where odour obviously has to be minimised. The outcome was the stabiliser Interstab 5216, now used to provide good film clarity and processing characteristics in extruded and blown packaging film, of the type used to wrap flowers. 

The variation in the optical properties of blown films is well expressed as a function of PI. Such findings show that the memory effects are strongly correlated to the end-use properties of LDPE and both the haze and gloss are controlled rather by an elastic response of the melt than by size of the crystallites and/or the crystallinity of the extruded film. One of the authors have pointed out in a previous paper that the overall haze of LDPE blown film might be controlled by the external haze which is attributed to surface roughness of the extruded film and is closely correlated to such viscoelastic properties as die swell and capillary end correction. The results obtained in this study further support our previous finding. 

In fact all of the biopolymers are injection-mouldable in practice and can even be blown into film quite successfully provided that care is taken to minimize melt temperatures and residence times. It is also possible to adopt inverted temperature profiles along extruders such that the polymer is first melted at a relatively high temperature and then conveyed to the die through much cooler zones. This further reduces thermal degradation. 

Dow Chemical claims a patent on a blend [11] with a decreased tendency toward delamination, which exhibits a desirable balance of properties, a high level of impact resistance, solvent resistance, and processability. The product can be blown into films, spun into fibers, extruded into sheets, formed into multilayer laminates, and molded into any desired shape and can be used in data storage apparatus, appliance and instrument housings, motor vehicle body panels, and other parts and components for use in electrical, automotive, and electronic industries. 

Ethylene vinyl acetate is processed by extrusion. The extruded film may be used to produce blown film, coated film, tubing, profiles, and extrusion blow moulded products. EVA should be kept under 230°C or it will begin to degrade. 

The properties of polypropylene made from sugarcane or corn are the same as conventional polyethylene. Polypropylene is a very versatile plastic and can be made into many different types of products that are injection molded, extruded into profile or sheet, blown into film or bottles, rotation molded into hollow parts, or compression molded into molded products. The properties of polypropylene are listed in Table 5.4 (MatWeb 2014). 

Figure 1 Scanning electron micrograph of the surface of extrusion-blown LDPE film containing 10% of maize starch. As the extruded tube is inflated and stretched, characteristic mounds are raised by the solid starch particles, average diameter 15gm. Magnification circa x350,...

The vibrational changes that occur on orientation and crystallization have been used to research the origin of the residual orientation frequently found in blown or extruded film. These materials frequently show quite well developed orientation, and hence are useful as shrink wrapping. As the flowing melts from which they are formed are optically dichroic, it seems reasonable to propose a model involving flow-orientation-crystallization and solidfication in an oriented manner. It has been shown, however, that the orientation of a flowing polyethylene melt (as measured by infrared, Raman diffraction and X-ray diffraction) is very small [38]. 

Burkholz JK, DeVries KL. NO and mechanical degradation of blown extruded nylon-6 film. J Blast. Film Sheeting 1998 14(l) 40-53. 

Blends of polymers (see Section 5.3) are also often used to form films, and such blown or extruded films can also benefit from examination by optical microscopy. One such study in which the blend is composed of LCP reinforced PE, a blown film used for balloon applications as different as weather balloons and angioplasty balloons, was examined by polarized optical... 

Because lyotropic liquid-crystalline polymers cannot be extruded, injection molded, or blown into films, other polymers that can be melt processed have been developed. These thermotropic liquid-crystalline polymers convert to a mesophase when the sohd polymer is heated to a temperature above the crystalline melting point. Thus, these polymers show three thermal transitions. In increasing order of temperature, these are glass transition temperature, erystalline melting... 

---