Polyester creep

High strength Stiffness at elevated temperatures Mineral reinforced Most economical Low warpagc Polyester (glass reinforced) High stiffness Lowest creep Excellent electrical properties properties... 

Polyester, thermoplastic TP polyesters have different grades. Polybutylene tereph-thalate (PBT) a crystalline polymer and an excellent engineering material. It has marginal chemical resistance but resists moisture, creep, fire, fats, and oils. Molded items are hard, bright colored, and retain their impact strength at temperatures as low as — 40°F (-40°C). Uses include auto louvers, under-the-hood electricals, and mechanical parts. 

Water is a natural plasticizer for many polar polymers such as the nylons (23K). polyester resins (239), and cellulosic polymers (240). It strongly shifts in epoxies (241.242). Thus the creep and stress-relaxation behavior of such polymers can be strongly dependent on the relative humidity or the atmosphere. 

Thermally stimulated creep (TSCr) method, 21 742-743 Thermally stimulated current spectrometry (TSC), 21 743 Thermal mass meters, 20 681 Thermal mechanical analysis (TMA), of polyester fibers, 20 21 Thermal motion, in silicon-based semiconductors, 22 237-238 Thermal noise, silicon-based semiconductors and, 22 237 Thermal oxidation, 10 77-78, 79 in VOC control, 20 683-685 Thermal oxidation rates, silicon, 22 490 Thermal oxidizers... 

Time-temperature shifting is used widely in the prediction of creep and creep-rupture in polyester geosynthetics. Creep of oriented polyesters is expressed by a linear or quadratic increase of strain with log (lifetime). The lifetime under constant load is expressed by the semilogarithmic formula ... 

Figure 8.7 First stage of the stepped isothermal method (SIM) for oriented polyester fibres. Creep strain is measured under a single load while the temperature is increased...

Time to rupture can be predicted by using the accelerated times generated by the creep data, and the creep-rupture characteristic generated by performing twelve of these tests over a range of loads. Conventional long-term creep strain and creep-rupture tests have so far confirmed the validity of the predictions for polyester fibres. Comments on the method have been published by Greenwood and Voskamp [10]. 

Figure 9.1 Schematic prediction of creep modulus of polyester fibres from time-temperature shifted data (based on information from [5])...

Sheet molding compounds (SMCs) and bulk molding compounds (BMCs) are the dominant materials used in automotive applications. These composites of unsaturated polyester resin, fillers and fiberglass have advantages of high stiffness, heat resistance and low coefficient of expansion. Coupled with low creep resistance, which is a distinct advantage over thermoplastic competition, and low-profile additives, which can yield Class A surfaces, these materials are well suited for applications from exterior body panels to under the hood components. 

TPUs are handicapped by a lower elasticity than conventional rubbers, the more so the higher the hardness certain risks of creep, relaxation and permanent set, the more so the higher the temperature higher cost than TPOs risks of hydrolysis especially for the polyester types UV exposure yellowing incompatibility between certain polyester and polyether grades aromatic and chlorinated hydrocarbon behaviour limited thermal behaviour density inherent flammability, but FR grades are marketed risks of fume toxicity in the event of fire. 

Part of the polyolefin family are PBs. They are similar to PPs and HDPEs but exhibit a more crystalline structure. This crystallinity produces unusual high strength and extreme resistance to deformation over a temperature range of-10 to 190F. Its structure results in a rubberlike, elastomeric material with low molded-in stress. Tensile stress that does not plateau after reaching its yield point makes possible films that look like PE but act more like polyester (TP) films. Compared to other polyolefins, they have superior resistance to creep... 

The thermal and UV stabilising action of linear, low molec.wt. unsaturated polyesters and epoxy resins in PVC was investigated using short-term tensile and long-term tensile creep testing and calculations of isochronous creep... 

Unprocessed PTFE resin is a white solid with a waxy appearance and feel. It has only a moderate tensile strength, much less than the nylons and polyesters. It also has a tendency to creep (or sag) under compression, but this can be accommodated in bearing applications by proper engineering... 

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