Fabrication of Plastics

An important step in the manufacture of any plastic product is the fabrication or the shaping of the article. Most polymers used as plastics when manufactured are prepared in pellet form as they are expelled from the reactor. These are small pieces of material a couple of millimeters in size. This resin can then be heated and shaped by one of several methods. Thermoset materials are usually compression molded, cast, or laminated. Thermoplastic resins can be injection molded, extruded, or blow molded most commonly, with vacuum forming and calendering also used but to a lesser extent. 

Class of Plastic Modulus Yield Stress Ultimate Tensile Strength Elongation at Break Examples 

Hard and strong Sti ess f High High High Moderate Rigid PVC Impact polystyrene Styrene—acrylonitrile 

Torpedo to ensure bringing of polymer into good themuM contact with walls 

Compression molding (Fig. 16.7) is practically the oldest method of fabricating polymers and is still widely used. The polymer is placed in one half of a mold and the second half compresses it to a pressure of about 1 ton/in. The powder is simultaneously heated, which causes the resin to cross-link. 

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Injection Molding. Matched metal molds are used in the fabrication of plastic closures, specialty packages, and botde preforms. In conventional injection mol ding the plastic resin is melted in an extmder which forces a measured quantity or shot into a precision-machined chilled mold after which the nozzle of the extmder is withdrawn. 

Plastics Fabrication and Processing. The apphcation of microwave or r-f energy in various stages of fabrication of plastic products is widespread. Most apphcations operate at low frequency, ca 27 MHz. The estabhshed processes are weU known (180). 

The fill illustrated in Figures 9-1 lOA and B is typical of many cooling tower heat transfer evaporative cooling surfaces. The wooden splash type is the oldest in terms of length of usage, while the film types (some fabricated of plastic) have been in service about 40 years [148]. 

The mechanical behavior of plastics is dominated by such viscoelastic phenomena as tensile strength, elongation at breaks, stiffness, and rupture energy, which are often the controlling factors in a design. The viscous attributes of plastic melt flow are also important considerations in the fabrication of plastic products. (Chapter 8, INFLUENCE ON PERFORMANCE, Viscoelasticity). 

There are conditions during the fabrication of plastic products that ensure meeting product performance requirements. However there are also constraints as reviewed in Chapter 8. 

Optical properties of the material are less critical for microchips hyphenated with MS than for devices with on-chip optical detection where low background absorption or fluorescence is mandatory. Thus, completely opaque polymers like glassy carbon or polyimide " can be used as microfabrication substrates. Furthermore, polymer microchips are of great interest because their potentially low manufacturing costs may allow them to be disposable. Methods used for the fabrication of plastic chips include laser ablation and molding methods. 

SP1 Plastics Engineering Handbook, 1976,4lhcd., Van Nostrand Reinliold, New York. This book is concerned with the commercial production of plastic items. However, it contains some information which is useful for the fabrication of plastic items in the laboratory or shop. 

Clearly, MIPs are becoming increasingly useful as promising candidates both for inspiration and fabrication of plastic antibodies and enzymes. This outcome ultimately strengthens the importance of MIPs for various envisioned chemosensor and biosensor applications. 

FIGURE 2.23 Scheme for fabrication of plastic microdevices from silicon master using an intermediate soft mold, (a) Silicon structures are fabricated using conventional photolithography and reactive ion etching, (b) PDMS is cured in situ over the silicon master, (c) Polystyrene is hot embossed onto the PDMS mold or polymerized in situ from partially polymerized styrene, (d) Polystyrene replica is separated from the mold [85]. Reprinted with permission from Springer Science and Business Media. 

Sudarsan, A.P., Ugaz, V.M., Printed circuit technology for fabrication of plastic-based microfluidic devices. Anal. Chem. 2004, 76, 3229-3235. 

A third approach to be considered is the ecological and sustainable aspects of a material. For instance, the fossil resources used for the fabrication of plastics constitute an undesirable contribution of carbon dioxide to the atmosphere thus increasing global warming. Moreover, the long persistence of some plastic materials in the environment causes visual pollution and suffocation of animals, if their disposal in the post-use period is not adequate. The energy consumption in the fabrication of a material also falls under this consideration. 

Blow molding—A process used in the fabrication of plastic bottles and other hollow shapes a heated tube of plastic (a preform or parison) is forced against the sides of a mold by air pressure. 

L. Martynova, L.E. Locascio, M. Gaitan, G. Kramer, R.G. Christensen and W.A. MacGrehan, Fabrication of plastic microfluid channels by imprinting methods. Anal. Chem., 69 (1997) 4783-4789. 

Plastic material manufacturers, machinery builders, specialty item distributors, and fabricators of plastics supply information concerning the use of their products as well as other information pertaining to fabrication of plastics. Some of the publications are extensive essays on various phases of plastics fabrication, while others are little more than descriptions of the products. Nevertheless, these sources of information are extremely important because of the lack of more formal presentations in standard textbooks and references. 

The term plastics is used instead of polymer to indicate a specific category of high molecular weight materials that can be shaped using a combination of heat, pressure, and time. All plastics are polymers, but not all polymers are plastics. In this text, we will discuss the major plastics that are useful as packaging materials. To a limited extent, we will discuss cellophane, which is a wood-based material that is a polymer, but not a plastic. We will also discuss adhesives, which are polymers and may or may not be plastics, but which are very useful in the fabrication of plastic and other types of packaging. 

Brister, P. C. and Weston, K. D., Patterned solvent delivery and etching for the fabrication of plastic microfluidic devices. Analytical Chemistry 77, 7478-7482, 2005. 

These esters were first produced early in the 19th century and resulted in changes in both military and industrial technology. For example, gun cotton replaced black powder as a propellant and celluloid was an early synthetic thermoplastic which initiated the molding and fabrication of plastics. 

The products are recovered from the MS W stream via curbside collection, separated/ sorted at MRFs, and then cleaned and ground into chips at plastic reclaiming facilities to be remelted into recycled resin pellets. The recycled resin is used, mixed with virgin plastics, in the fabrication of plastic products. Mechanical recycling works best when applied to source-separated streams of waste plastics products. 

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