Transparency of plastics

Many of the polymers used to make plastics have two unique characteristics They are transparent and can be melted repeatedly to form new things. The transparency of plastic is important in many products. Food wraps, beverage bottles, headlights, and contact lenses are all made of transparent plastics. The ability of plastics to be melted and shaped into new things makes them suitable for recycling. 

Chronologically the implications for enhanced shear ductility in Figure 4 prodded us to convert BPF polycarbonate—a transparent but brittle and useless polymer—into a transparent, tough, and potentially useful material. The results of the efforts on both families of resins indicate a general recipe for toughening that does not compromise the transparency of plastics. 

The chapter begins by introducing the concepts behind microwave heating and the properties that make plastics transparent to this kind of radiation. This is followed by a definition of microwave pyrolysis of plastics and the ways that microwave transparency of plastics can be overcome in order to use this microwave energy as a source of heat for pyrolysis. A number of microwave pyrolytic processes for materials other than plastics are also introduced. 

D 1003-61, BS 2782 (515A). Again expressed as a percentage See-through D1746-62T (Transparency of plastic sheeting). Clarity BS 4618 Section 5.3. 

ASTM D1746 Standard Test Method for Transparency of Plastic Sheeting. Used to determine the regular transmittance (Tr) of plastic sheeting. The primary use of D1746 is with nominally clear and colorless thin sheeting, but the method is generally applicable to any translucent or transparent material. 

Clarity-enhancing agents provide a site within the polymer resin where crystallization may occur. This allows smaller crystallites to form. The smaller crystallites allow light to travel through the polymer medium and avoid diffraction of the light (4). The transparency of plastics can be measured according to a standard test method (5). 

Plastic. A plastic bag usuaUy consists of a single heavy waU of plastic film, woven sheets of plastic tape, or laminates. Principal materials of constmction are polyethylene and polypropylene (see Fibers, olefin). Both transparent and opaque sheeting are used, and printabUity usuaUy is exceUent. Plastic bags can be fiUed and closed with conventional equipment beat-sealing is essential for open-mouthed bags to effect a moisture barrier. 

During this period, the ICI laboratories were also making their other great contribution to the range of plastics materials—the product which they marketed as Perspex, poly(methyl methacrylate). As a result of work by two of their chemists, R. Hill and J. W. C. Crawford, it was found that a rigid transparent thermoplastics material could be produced at a commercially feasible cost. The material became invaluable during World War II for aircraft glazing and to a lesser extent in the manufacture of dentures. Today poly(methyl methacrylate) is... 

It is an unfortunate fact that many students and indeed design engineers are reluctant to get involved with plastics because they have an image of complicated materials with structures described by complex chemical formulae. In fact it is not necessary to have a detailed knowledge of the structure of plastics in order to make good use of them. Perfectly acceptable designs are achieved provided one is familiar with their perfonnance characteristics in relation to the proposed service conditions. An awareness of the structure of plastics can assist in understanding why they exhibit a time-dependent response to an applied force, why acrylic is transparent and stiff whereas polyethylene is opaque and flexible, etc., but it is not necessary for one to be an expert... 

Optical Properties. The optical properties of a plastic which are important are refraction, transparency, gloss and light transfer. The reader is referred to BS 4618 1972 for precise details on these terms. Table 1.9 gives data on the optical properties of a selection of plastics. Some plastics may be optically clear (e.g. acrylic, cellulosics and ionomers) whereas others may be made transparent. These include epoxy, polycarbonate, polyethylene, polypropylene, polystyrene, polysulphone and PVC. 

Most of the above can be made into plastic films - primarily used for wrapping. Film properties vary widely from permeable for food to impermeable to preserve dryness. Paper, treated or untreated, has been used for many years as a covering film, but has low strength when wet and is difficult to make transparent. In the 1920s, the transparency of cellophane revolutionized wrap. It is regenerated cellulose, like viscose rayon, except it is extruded in sheet instead of fiber, unfortunately it is sensitive to water and humidity. 

Methylpentene polymer, a light plastic, has a crystalline melting point of 464 retention up to 392° F, transparency of 92%, and electrical properties similar to fluoroethylene. Its impact strength is greater than polystyrene and polymethyl methacr resistant to alkalies, weak acids, and non-chlorinated solvents. It may be injection m< implements for food packaging and preparation, medical care, and non-stick coating ... 

Acrylic is a generic name for derivatives of acrylic acid, of which methyl methacrylate is the most important. Polymerization is controlled to produce chain length of 800 to 3,000 monomer units. A small amount of plasticizer such as dibutyl phthalate may be added before bulk polymerization to assist in deep molding. The outstanding property of polymethyl metliacrylate is 0 transparency resistance to ultraviolet radiation from fluorescent lamps and ability to be... 

The application for plastics most widely known, based on the transparency and clarity of plastics, is their use as a window or... 

This photoelastic stress analysis is a technique for the nondestructive determination of stress and strain components at any point in a stressed product by viewing a transparent plastic product. If not transparent, a plastic coating is used such as certain epoxy, polycarbonate, or acrylic plastics. This test method measures residual strains using an automated electro-optical system. 

These qualities are considered in most applications for transparent plastics, forming a basis for directly comparing the transparency of various grades and types of plastic. The data are of value when a material is considered for optical purposes. Many transparent plastics do not have water clarity, and, for this reason, the data should indicate whether... 

Fogging of plastic films used for packaging or agriculture, spectacle lenses, crash helmets, etc., is caused by water droplets. This decreases the transparency and is aesthetically not desirable. 

Optical fibres composed of plastics are also transparent in the visible spectral region but optical losses reach 102 - 103 dB/km13. Their refractive index varies from 1.35 to 1.6 depending on the kind of polymer used (e.g. polymethymethacrylate PMMA -1.49). The chemical resistance is much worse than that of silica fibres and thermal stability is incomparable. On the other hand, low temperature processes of plastic fibre preparation allow us mix the starting polymer with organic dyes which enables the production of luminescent fibres suitable e.g. for fluorescence-based sensing13. 

Transparent flexible plastic substrates for organic light-emitting devices Y. Hong, Z. He, N.S. Lennhoff, D.A. Banach, J. Kanicki Journal of Electronic Materials, 33 312-320... 

In the modern world, we are accustomed to taking the chemical stability of glass very much for granted - we rely on the durability of glass for so many things, such as windows and (until the widespread availability of plastics) bottles, as well as its use in the chemical laboratory as an extremely inert and unreactive container. In addition to its apparent inertness, glass has a number of other beneficial properties, such as its transparency or the ability to take on virtually any colour as the result of the addition of a small amount of transition metals. 

Solvent dyes are also used for tinting transparent varnishes and lacquers in the furniture and leather industries, where the surface texture of the finished articles needs to be protected but not obscured. There is also a growing demand for coloured but transparent inks for printing on the ever-increasing amounts of plastic packaging of all kinds used for the food sold in supermarkets. 

The lightfastness of transparent systems matches step 7 to 8 on the Blue Scale, depending on the type of plastic and on the pigment content. In white reductions, at 1/3 to 1/100 SD, the pigment scores between step 8 and step 6. 

This type of degradation can also be referred to as photodegradation or ultraviolet (UV) degradation. It includes photo-oxidation. It produces some of the more familiar signs of degradation of plastics embrittlement, discoloration and loss of transparency. 

The market appeal of plastics is important for numerous applications such as packaging, automotive,appliances. .. Colour,transparency,gloss and odour contribute to make aplastic part attractive, unappealing or repulsive. 

Cellulosics are appreciated for their easy processability aesthetics transparency high gloss pleasant feel aptitude for colouring and decoration low electrostatic build up balance of fair mechanical properties and chemical resistance to oils, greases and aliphatic hydrocarbons possibilities of plasticization allowing very low moduli to be obtained fair electrical insulating properties fair performance/cost ratios food contact possibilities. 

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