Plasticizer shape, effect

Fourth, molded-in metal should be avoided whenever alternate methods will accomplish the desired objective. If it is essential to incorporate such inserts, they should be shaped so that they will present no sharp inside comers to the plastic. The effect of the sharp edges of a metal insert would be the same as explained in the first point above, namely, brittleness and stress concentration can occur. The cross-section that surrounds a metal insert should be heavy enough that it will not crack upon cooling. A method of minimizing cracking around the insert is to heat the... 

Effect of Plasticizer Shape. Extended plasticizer molecules such as aliphatic chains with a high degree of flexibility, usually lower Tg or Tc much more than bulky plasticizer molecules, such as those containing ring structures. However, Table XIII shows that the comparison between aliphatic and aromatic ester plasticizers is also determined by the length of the alcohol residues and by separation between the ester groups. 

Mechanical Properties and Structural Performance. As a result of the manufacturing process, some cellular plastics have an elongated cell shape and thus exhibit anisotropy in mechanical, thermal, and expansion properties (35,36). Efforts are underway to develop manufacturing techniques that reduce such anisotropy and its effects. In general, higher strengths occur for the paraHel-to-rise direction than in the perpendicular-to-rise orientation. Properties of these materials show variabiUty due to specimen form and position in the bulk material and to uncertainty in the axes with respect to direction of foam rise. Expanded and molded bead products exhibit Httie anisotropy. 

The effective interfacial area depends on a number of factors, as discussed in a review by Charpentier [C/j m. Eng.J., 11, 161 (1976)]. Among these factors are (1) the shape and size of packing, (2) the packing material (for example, plastic generally gives smaller interfacial areas than either metal or ceramic), (3) the liquid mass velocity, and (4), for smaU-diameter towers, the column diameter. 

Other factors such as the use of additives also have an effect on the shape of the flow curves. Flame retardants, if used, tend to decrease viscosity whereas pigments tend to increase viscosity. Fig. 5.17 shows flow curves for a range of plastics. 

The selection of the evaluation method(s) depends on the specific type of plastic, the environment of the evaluation, the effectiveness of the evaluation method, the size of the structure, the fabricating process to be used, and the economic consequences of structural failure. Conventional evaluation methods are often adequate for baseline and acceptance inspections. However, there are increasing demands for more accurate characterization of the size and shape of defects that may... 

Internal plastic thread The strength of plastic threads is limited, and when molded in a product involving either an unscrewing device or a rounded shape of thread similar to bottle-cap threads, they can be stripped from the core. Screw threads, when needed, should be of the coarse type and have the outside of the thread rounded so as not to present a sharp V to the plastic that can produce a notch effect. 

Molded-in insert If metal inserts are to be molded into a plastic product consideration should be given to wall thickness around the insert (Table 3-18) and their shape. The shape should present no sharp edges to the plastic, since the effect of the edges would be similar to that of a notch. A knurled insert... 

Distortion Another problem with extrusions is caused by distortion of the section by the effect of heat and other environmental conditions such as exposure to water or chemical agents that tend to soften the plastic. These distortions are generally reversals of the profile back to the shape that it had exiting in the die. This action indicates that the post die forming operations were done at a lower than desirable temperature which results in a molded-in stress. When the stress is relieved the product distorts. In some instances these stresses cannot be eliminated by process changes so that the product is inherently deficient in performance. 

The moisture content of a plastic affects such conditions as electrical insulation resistance, dielectric losses, mechanical properties, dimensions, and appearances. The effect on the properties due to moisture content depends largely on the type of exposure (by immersion in water or by exposure to high humidity), the shape of the product, and the inherent behavior properties of the plastic material. The ultimate proof for tolerance of moisture in a product has to be a product test under extreme conditions of usage in which critical dimensions and needed properties are verified. Plastics with very low water-moisture absorption rates tend to have better dimensional stability. 

This subject effects designers since many products have the requirement by regulations or otherwise to use recycled plastics. Different methods are used to recycle materials to provide plastics with a continuing life. Method used is influenced by factors such as costs, quantity involved, weight involved, size and shape, complexity of mixed types of plastics, extended of contamination such as metallic particles, continued availability of material, etc. (Recognize that they can also be used as energy sources through incineration that can be combined with production of electricity and/or hot water for example). 

Efforts to improve IUDs have led to the use of medicated devices. Two types of agents are generally used—contraceptive metals and steroid hormones. The metal device is exemplified by the CU-7, a polypropylene plastic device in the shape of the number 7. Copper is released by a combination of ionization and chelation from a copper wire wrapped around the vertical limb. This system is effective for up to 40 months. 

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