Polystyrene electrical properties

General-Purpose Polystyrene. Polystyrene is a high molecular weight M = 2 — 3 x 10 ), crystal-clear thermoplastic that is hard, rigid, and free of odor and taste. Its ease of heat fabrication, thermal stabiUty, low specific gravity, and low cost result in mol dings, extmsions, and films of very low unit cost. In addition, PS materials have excellent thermal and electrical properties that make them useful as low cost insulating materials (see Insulation, ELECTRIC Insulation, thermal). 

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 ... 

Siloxane containing interpenetrating networks (IPN) have also been synthesized and some properties were reported 59,354 356>. However, they have not received much attention. Preparation and characterization of IPNs based on PDMS-polystyrene 354), PDMS-poly(methyl methacrylate) 354), polysiloxane-epoxy systems 355) and PDMS-polyurethane 356) were described. These materials all displayed two-phase morphologies, but only minor improvements were obtained over the physical and mechanical properties of the parent materials. This may be due to the difficulties encountered in controlling the structure and morphology of these IPN systems. Siloxane modified polyamide, polyester, polyolefin and various polyurethane based IPN materials are commercially available 59). Incorporation of siloxanes into these systems was reported to increase the hydrolytic stability, surface release, electrical properties of the base polymers and also to reduce the surface wear and friction due to the lubricating action of PDMS chains 59). 

More expensive than commodities such as polyolefins, PVC and polystyrene brittle when dry, sensitive to water (swelling up to 10%, decrease in mechanical and electrical properties) opaque or translucent require UV and weathering protection significant shrinkage after moulding inherent flammability (but FR grades are marketed). 

In this context numerous changes were made. The chapter Properties of Polymers was revised and a new section Correlations of Structure and Morphology with the Properties of Polymers was added. The chapter Characterization of Macromolecules was revised and enlarged. 15 examples have been deleted as they did no longer represent the state of the art and/or were of minor educational value. Several new experiments (plus background text) were added, as, for example controlled radical polymerization - enzymatic polymerization - microemulsions - polyelectrolytes as superabsorbants - hyperbranched polymers - new blockcopolymers - high impact polystyrene - electrical conducting polymers. 

In general, polystyrene is used in applications where ease of fabrication and decorability arc required. Polystyrene has excellent electrical properties, good thermal and dimensional stability, lesistance to staining, and low cost. General purpose polystyrene is preferred where clarity is also of prime concern, Impact polystyrene is preferred where toughness is needed.)... 

The resultant cured product will have a density of approximately 112 kg/m (7 Ib/ft ), with a compressive strength of 0.69 MPa (100 psi). The polystyrene microspheres have about the same physical and electrical properties as those obtained with other organic syntactic foam fillers. 

Step 16. Calculate the key electrical properties. The dielectric constant at room temperature can be calculated from equations 9.11 and 9.12. For polystyrene, e(298K)=2.57 is predicted. The predicted e(298K) can be inserted into Equation 9.7, to predict the volume resistivity at room temperature. The prediction for polystyrene is 7.2 1017 ohnvcm. For polar polymers, these two properties can only be predicted at T=298K with the present correlations. 

Electrical Measurements. The electrical properties of polymers have much in common with mechanical properties. They can be divided into static properties equivalent to direct current properties and dynamic properties resulting from alternating current measurements. The most used parameter is the volume or bulk resistivity (ASTM-D257-75b) which is the resistance in ohms of a material 1 cm thick and 1 cm2 area. Bulk resistivity is one of only a few properties that vary nearly 1025 in typical use (materials with values above 10 ohm-cm for polystyrene to 10 5 ohm-cm for copper). 

The fabrication and electrical properties of carbon nanofiber-polystyrene composites and their potential applications for EMI shielding have been reported [42]. Being lightweight is a key technological requirement for the development of practical EMI shielding systems. Thus the fabrication of foam structures to further reduce the weight of carbon nonofiber-ploymer composites has been recently demonstrated and simple preparation routine has been reported [43] by which this novel foam structure can be prepared. 

The optical properties, clarity and gloss, are also improved and biaxially oriented polystyrene and polypropylene films are used for envelope windows and overwraps. Biaxially oriented polyvinylidene chloride film is also used for food packaging in view of its good mechanical and optical properties, but for economic reasons it is only used if its low permeability to gases, especially oxygen, is required. The electrical properties are improved by biaxial orientation and the applications of polyester, polycarbonate and polypropylene films in capacitors are expected to show a rapid growth. In these electrical applications crystalline films are always annealed in order to improve the dimensional heat stability. 

Around 8% bromine content in the final PBT compound is sufficient to achieve the V-0 test rating for all types of brominated flame retardants, but some affect the physical and mechanical properties of the resultant materials more than others. Polymeric brominated styrene additives would be preferred in glass-filled compounds. Brominated polystyrene, such as Saytex HP-7010 from Albemarle Corp. and poly(dibromostyrene) are such materials. They retain excellent properties after heat ageing. High impact strengfti and excellent electrical properties are especially noted for HP-7010 due to the additive s high purity and low aliphatic halogen content. 

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