Polyolefin orientation

Hard baked goods such as cookies and crackers have a relatively low water and high fat content. Water can be absorbed, and the product loses its desirable texture and becomes subject to Hpid rancidity. Packagiag for cookies and crackers includes polyolefin-coextmsion film pouches within paperboard carton sheUs, and polystyrene trays overwrapped with polyethylene or oriented polypropylene film. Soft cookies are packaged in high water-vapor-barrier laminations containing aluminum foil. 

These models are usually overall plant or corporation oriented and are geared toward running the business. If utilities are included, they are probably keyed to production levels of operating units or, in the case of the polyolefin plant, a characteristic set of utilities is charged against each unit of each specialty product. Often, recycle streams within segments of the operation are not pertinent and not included. 

Wet processes involve mixing a hydrocarbon liquid or some other low-molecular -weight substance with a polyolefin resin, heating and melting the mixture, extruding the melt into a sheet, orientating the sheet either in the machine direction or biaxi-ally, and then extracting the liquid with a volatile solvent [6-8]. 

Dry processes involve melting a polyolefin resin, extruding it into a film, thermal annealing, orientation at a low temperature to form micropore initiators, and then orientation at a high temperature to form micropores [9, 10]. The dry process involves no solvent handling, and therefore is inherently simpler than the wet process. The dry process involves only virgin polyolefin resins and so presents little possibility of battery contamination. 

The operating pressures and shear rates in the extrusion process are considerably lower than they are in molding. As it exits the die, but not necessarily when it leaves the process, the material is in an essentially stress-free condition. Depending on the wall thickness of the material and the particular material, there is orientation of the plastic to a greater or lesser controllable degree. Thin walls produce higher orientation in materials such as PP, that is a highly crystalline polyolefin, and which orients much more than materials such as PVC. 

Chodak [257] has reviewed the properties (include mechanical, processing, orientation) of radiation (UV, y, EB) of polyolefin-based materials include PE, PP, and their blends based on... 

Stretched Polymers MF membranes may be made by stretching (Fig. 20-68). Semicrystalline polymers, if stretched perpendicular to the axis of crystallite orientation, may fracture in such a way as to make reproducible microchannels. Best known are Goretex produced from Teflon , and Celgard produced from polyolefin. Stretched polymers have unusually large fractions of open space, giving them very high fluxes in the microfiltration of gases, for example. Most such materials are very hydrophobic. 

Peroxidic groups in oxidized polyolefins have frequently been employed as sources of free radicals to allow grafting of vinyl monomers to polyolefins (2f[). Some of the products from the gas reactions also have interesting potential as reactive sites. For example, chloroformate groups are well known to react with alcohols, and amines 2J[). Thus chloroformate groups could be useful for example in coupling highly oriented polyolefin fibres to resins such as epoxy based systems. 

ARA Palmans, M Eglin, A Montali, C Weder, and P Smith, Tensile orientation behavior of alkoxy-substituted BA(phenylethynyl)benzene derivatives in polyolefin blend films, Chem. Mater., 12 472-480, 2000. 

The process for making lithium-ion battery separators can be broadly divided into dry - and weH processes. Both processes usually employ one or more orientation steps to impart porosity and/or increase tensile strength. The dry process involves melting a polyolefin resin, extruding it into a film, thermally... 

Polyolefin foams are easier to model than polyurethane (PU) foams, since the polymer mechanical properties does not change with foam density. An increase in water content decreases the density of PU foams, but increases the hard block content of the PU, hence increasing its Young s modulus. However, the microstructure of semi-crystalline PE and PP in foams is not spherulitic, as in bulk mouldings. Rodriguez-Perez and co-workers (20) showed that the cell faces in PE foams contain oriented crystals. Consequently, their properties are anisotropic. Mechanical data for PE or PP injection mouldings should not be used for modelling foam properties. Ideally the mechanical properties of the PE/PP in the cell faces should be measured. However, as such data is not available, it is possible to use data for blown PE film, since this is also biaxially stretched, and the texture of the crystalline orientation is known to be similar to that in foam faces. 

Cast film extrusion of polyolefins has been developed to obtain flexible films with a high level of transparency by freezing the amorphous polymer structure of the melt on a chill roll. Cast films are mono-oriented in extrusion direction. 

The existence of a second class of complex phases, the modulated and perforated layer structures, has largely been explored by Bates and co-workers (Forster et al. 1994 Hamley et al. 1993, 1994 Khandpur et al. 1995 Schulz et al. 1996), who used SANS and TEM to investigate shear oriented structures. The thermally-induced phase transition from the lam to the hex phase in polyolefin diblocks was studied in detail by Hamley et al. (1993, 1994) using SANS, TEM and rheology. Intermediate hexagonal modulated lamellar (HML) and hexagonal perforated layer (HPL) structures were observed on heating PEP-PEE, PE-PEP and PE-PEE diblocks, where PEP is poly(ethylene-propylene), PEE is... 

MC MDI MEKP MF MMA MPEG MPF NBR NDI NR OPET OPP OSA PA PAEK PAI PAN PB PBAN PBI PBN PBS PBT PC PCD PCT PCTFE PE PEC PEG PEI PEK PEN PES PET PF PFA PI PIBI PMDI PMMA PMP PO PP PPA PPC PPO PPS PPSU Methyl cellulose Methylene diphenylene diisocyanate Methyl ethyl ketone peroxide Melamine formaldehyde Methyl methacrylate Polyethylene glycol monomethyl ether Melamine-phenol-formaldehyde Nitrile butyl rubber Naphthalene diisocyanate Natural rubber Oriented polyethylene terephthalate Oriented polypropylene Olefin-modified styrene-acrylonitrile Polyamide Poly(aryl ether-ketone) Poly(amide-imide) Polyacrylonitrile Polybutylene Poly(butadiene-acrylonitrile) Polybenzimidazole Polybutylene naphthalate Poly(butadiene-styrene) Poly(butylene terephthalate) Polycarbonate Polycarbodiimide Poly(cyclohexylene-dimethylene terephthalate) Polychlorotrifluoroethylene Polyethylene Chlorinated polyethylene Poly(ethylene glycol) Poly(ether-imide) Poly(ether-ketone) Polyethylene naphthalate Polyether sulfone Polyethylene terephthalate Phenol-formaldehyde copolymer Perfluoroalkoxy resin Polyimide Poly(isobutylene), Butyl rubber Polymeric methylene diphenylene diisocyanate Poly(methyl methacrylate) Poly(methylpentene) Polyolefins Polypropylene Polyphthalamide Chlorinated polypropylene Poly(phenylene oxide) Poly(phenylene sulfide) Poly(phenylene sulfone)... 

The main requirements for good textile fiber are (a) a Tt below room temperature (to provide flexibility at normal temperatures), together with (b) microcrystallinity to provide strength, orientability, and (sometimes) ease of fabrication by melting. The classical organic polymers used for fibers (Nylons, polyesters, and polyolefins) generally have these characteristics. 

If the orientation process in semi-crystalline fibres is carried out well below the melting point (Tm), the thread does not become thinner gradually, but rather suddenly, over a short distance the neck. The so-called draw ratio (A) is the ratio of the length of the drawn to that of the undrawn filament it is about 4-5 for many polymers, but may be as high as 40 for linear polyolefins and as low as 2 in the case of regenerated cellulose. 

An important area for PVC is the water transportation market and there has been competition from polyolefins in this area. The PVC producers have responded by introducing foam core pipe, for improved cost effectiveness. In another development, orientation during processing gives improved impact resistance (195). More details follow in subsequent sections. 

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