Polypropylene thermal resistance

Polyolefins (Polyethylene, Polypropylene) Powder, pellets Tough and chemical resistant. Weak in creep and thermal resistance. Polyethylene maximum use temperature 210 F, polypropylene 260 F. May be injection and extrusion molded, vacuum formed. Low cost. Antistatic sheet and tiles, heat-shrinkable tubing, deicer boots. 

Gay is used as a filler in compounding paper and rubber. Talc, a naturally occurring fibrouslike hydrated magnesium silicate, is used to improve the thermal resistance of polypropylene (PP). Since talc-filled PP is much more resistant to heat than unfilled PP, it is used in automotive accessories subject to high temperatures. Over 40 million tons of talc are used annually as a filler. 

Flammability. Most polyolefins can be made fire retardant using a stabilizer, usually a bromine-containing organic compound, and a synergist such as antimony oxide. However, the required loadings are usually too high for fibers to be spun. Fire-retardant polypropylene fibers exhibit reduced light and thermal resistance. 

Isotactic polypropylene is a rather stiff and tough solid material with a melting point of 164°C. Closely packed, CHs-studded helices (Figure 17), rigidly interwoven in crystalline domains (Figure 18), account for the mechanical and thermal resistance of isotactic polymers. Syndiotactic polypropylene has a related crystalline structure, but atactic polymers are amorphous and form oily or waxy materials depending on chain lengths. 

All of these materials-brick, mortars and membranes-will be fully discussed in later chapters along with (1) Castables, grouts, and polymer concretes (2) Monolithics (troweled, sprayed and gunned linings) and (3) Expansion joint compounds, plus rigid plastic fabrications such as polyethylene, polypropylene and PVC. These components made from a whole host of materials are effectively used in a wide variety of industrial applications requiring superior chemical and thermal resistance. 

The introduction of oxygen into the hydrocarbon chain of polymers rednces their thermal stability. This trend is illustrated by the examples of polyformaldehyde (T g = 170 "C), polyethylene oxide (PEO Tjg= 345 °C), isotactic polypropylene oxide (iPPO Tjg = 195 °C) and atactic polypropylene oxide (T = 295 "C) here thermal resistances are lower than those in the corresponding hydrocarbon polymers, namely polyethylene (T g = 406 "C) and polypropylene (T g = 390 °C). 

In the early 1960s, an industry started to develop around the modification of polymers. This industry originally started as a way to simply modify polymer for improvements of impact resistance, color, or thermal stability. It initially used many tools of the rubber industry to modify polymers for specific end-use applications. Polypropylene with its useful balance of properties has found interesting utility in the automotive industry. This market penetration of PP was primarily due to its good thermal resistance for under-the-hood applications, its ease of colorability for applications on the interior of the car, and its low raw material cost. Today, the modification of PP is a large industry, often associated with the PP production or in some cases completely independent of the polymerization steps itself. 

Polypropylene (PP) has wide acceptance for use in many application areas. However, low thermal resistance complicates its general practice. The new approach in thermal stabilization of PP is based on the synthesis of PP nanocomposites. This paper discusses new advances in the study of the thermo-oxidative degradation of PP nanocomposite. The observed results are interpreted by a proposed kinetic model, and the predominant role of the one-dimensional diffusion type reaction. According to the kinetic analysis, PP nanocomposites had superior thermal and fireproof behavior compared with neat PP. Evidently, the mechanism of nanocomposite flame retardancy is based on shielding role of high-performance carbonaceous-silicate char which insulates the underlying polymeric material and slows down the mass loss rate of decomposition products. 

Both chemical and physical characteristics of polypropylene resemble high density polyethylene, but polypropylene is clearer, harder, has a lower density and a better thermal resistance (polypropylene can be steam sterilised). Polypropylene is less resistant to low temperatures than high density polyethylene. The chemical resistance of polypropylene is good (see Table 24.2). To protect polypropylene from oxidation, antioxidants are always added. Resistance to gamma sterilisation is relatively poor, but can be enhanced by additives. 

The thermal resistance of the nickel-cadmium batteries is also very good. These batteries can withstand temperatures up to 70°C or more without mechanical damage. Cells in polypropylene or steel containers are the best in this respect. Saline or corrosive environments present no problems for cells in plastic containers. 

The thermal resistance of non-stabilized polypropylene is lower than that of polyethylene. Polypropylene also emits more volatile components at lower temperatures in the form of saturated and unsaturated aliphatic hydrocarbons. Actual activation energy for strictly thermal degradation is lower than expected the available data vary between 124 and 260 kj/mol. Activation energy for oxidative degradation ranges from 65 to 85 kJ/mol [755], [756]. 

As can be seen, the hardness, the tensile and flexure properties and the thermal resistance (HDT, Vicat) generally increase with higher fiber loading, with however a large scatter that likely reflects the various grades of polypropylene used, as well as (unknown) differences in compounding processes. E-glass fibers are the most common type but the actual fiber dimensions are... 

This polymer is typical of the aliphatic polyolefins in its good electrical insulation and chemical resistance. It has a melting point and stiffness intermediate between high-density and low-density polyethylene and a thermal stability intermediate between polyethylene and polypropylene. 

The preceding structural characteristics dictate the state of polymer (rubbery vs. glassy vs. semicrystalline) which will strongly affect mechanical strength, thermal stability, chemical resistance and transport properties [6]. In most polymeric membranes, the polymer is in an amorphous state. However, some polymers, especially those with flexible chains of regular chemical structure (e.g., polyethylene/PE/, polypropylene/PP/or poly(vinylidene fluoride)/PVDF/), tend to form crystalline... 

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