Melting point softening

Sheet forming processes, such as vacuum forming, do have effects on the product. The designer should be aware that these will affect the performance of one s product and one should learn how to modify the design to minimize any deleterious effects. Probably the most serious problem encountered in formed film or sheet products results from the fact that the materials are made from film or sheet at temperatures well below the melt softening point of the plastic, usually near the heat distortion temperature for the material. Forming under these condition when the draw down ratio is exceeded for a specific plastic can result in over stretched orientation of the material, the production of frozen-in stresses, poor product reproducibil-... 

As mentioned above, P3ATs are also melt-processable. The melting/softening point of P3ATs depends on the chain length of the alkyl group [44] (table 4.)... 

Thermoforming. Thermoforming is the most common method of fabricating sheet into three-dimensional packaging. In conventional thermoforming, the sheet is heated to its softening point or just below the melting temperature. The softened plastic is forced by differential air pressure into an open-top mold to assume the shape of the female mold. The mold is chilled and the plastic sheet solidifies and is then removed from the mold. 

Most hydrocarbon resins are composed of a mixture of monomers and are rather difficult to hiUy characterize on a molecular level. The characteristics of resins are typically defined by physical properties such as softening point, color, molecular weight, melt viscosity, and solubiHty parameter. These properties predict performance characteristics and are essential in designing resins for specific appHcations. Actual characterization techniques used to define the broad molecular properties of hydrocarbon resins are Fourier transform infrared spectroscopy (ftir), nuclear magnetic resonance spectroscopy (nmr), and differential scanning calorimetry (dsc). 

In order to increase the solubiUty parameter of CPD-based resins, vinyl aromatic compounds, as well as other polar monomers, have been copolymerized with CPD. Indene and styrene are two common aromatic streams used to modify cyclodiene-based resins. They may be used as pure monomers or contained in aromatic steam cracked petroleum fractions. Addition of indene at the expense of DCPD in a thermal polymerization has been found to lower the yield and softening point of the resin (55). CompatibiUty of a resin with ethylene—vinyl acetate (EVA) copolymers, which are used in hot melt adhesive appHcations, may be improved by the copolymerization of aromatic monomers with CPD. As with other thermally polymerized CPD-based resins, aromatic modified thermal resins may be hydrogenated. 

An important property recommending the use of LLDPE in many packaging appHcations is thek sealabHity. CompositionaHy uniform resins are especiaHy attractive for such use because thek melting and softening points are 15—20°C lower than those of commodity LLDPE resins (Fig. 1). 

Pontia.na.k. This resin is a copal and is similar to the alcohol-soluble Manilas. It is partially fossilized, so it melts at a higher temperature. Softening points range from 99—135°C, and acid numbers from about 112—120. Pontianak [9000-14-0] is used in specialty coatings and adhesives. 

Built-up roofing constitutes several pHes of a saturated roofing felt (low melt, flexible asphalt saturant) with each ply mopped in place and the stmcture covered by air-blown asphalts of from 60° to 105°C softening point, with the hardness selected depending primarily on roof slope. These roofs are usually surfaced with mineral aggregates. 

Carbon electrodes are the normal choice for the link in the connection chain to deflver power to the arc tip. Graphite may be used in special apphcations, but the higher cost of graphite favors the use of carbon electrodes. Carbon possesses properties ideal to its appHcation as an electrode. These properties include no softening point, no melting point, electrical conductivity, strength increases with increasing temperature, resistivity drops as temperature increases, available in the size and purity desired, and cost effectiveness. 

Blends with styrenic block copolymers improve the flexibiUty of bitumens and asphalts. The block copolymer content of these blends is usually less than 20% even as Httie as 3% can make significant differences to the properties of asphalt (qv). The block copolymers make the products more flexible, especially at low temperatures, and increase their softening point. They generally decrease the penetration and reduce the tendency to flow at high service temperatures and they also increase the stiffness, tensile strength, ductility, and elastic recovery of the final products. Melt viscosities at processing temperatures remain relatively low so the materials are still easy to apply. As the polymer concentration is increased to about 5%, an interconnected polymer network is formed. At this point the nature of the mixture changes from an asphalt modified by a polymer to a polymer extended with an asphalt. 

In the case of crystalline polymers such as types E and F the situation is somewhat more complicated. There is some change in modulus around the which decreases with increasing crystallinity and a catastrophic change around the. Furthermore there are many polymers that soften progressively between the Tg and the due to the wide melting range of the crystalline structures, and the value determined for the softening point can depend very considerably on the test method used. 

Figure II.5. Variation of Vicat softening point (5 kg load) with isotactic index and melt flow index.

Compared with atactic polypropylene it has a lower softening point (less than 100°C compared with 154°C when assessed by ball and ring methods), has better resistance to subzero temperatures and is completely soluble in aliphatic hydrocarbons. The molecular mass of atactic polybut-l-ene is about twice that of an atactic polypropylene of similar melt viscosity. 

Polymers of a-methylstyrene have been marketed for various purposes but have not become of importance for mouldings and extrusions. On the other hand copolymers containing a-methylstyrene are currently marketed. Styrene-a -methylstyrene polymers are transparent, water-white materials with BS softening points of 104-106°C (c.f. 100°C for normal polystyrenes). These materials have melt viscosities slightly higher than that of heat-resistant polystyrene homopolymer. 

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