Plastics, appearance tests

The above-mentioned codes contain requirements for accelerated durabiUty tests. In addition, interlayer manufacturers and laminators expose test samples for several years under extreme weather conditions, eg, the Florida coast and Arizona desert. The laminated products weather extremely well, with no change in the plastic interlayer. Occasionally, clouding is noted around the edges when exposed to high humidity for long periods, but this is reversible. Colored areas of PVB laminates may fade while subjected to extensive uv/solar irradiation, which could cause an appearance issue. This has not, however, been shown to alter the laminate s other performance properties. 

Occasionally, materials are tested in tension by applying the loads in increments. If this method is used for plastics then special caution is needed because during the delay between applying the load and recording the strain, the material creeps. Therefore if the delay is not uniform there may appear to be excessive scatter or non-linearity in the material. In addition, the way in which the loads are applied constitutes a loading history which can affect the performance of the material. A test in which the increments are large would quite probably give results which are different from those obtained from a test in which the increments were small or variable. 

TTie strain readings of a creep test can be more accessible to a designer if they are presented as a creep modulus. In a viscoelastic material, namely plastic, the strain continues to increase with time while the stress level remains constant. Since the creep modulus equals stress divided by strain, we thus have the appearance of a changing modulus. 

Most of over six million dentures produced annually in the USA are made of acrylics (PMMAs) that includes full dentures, partial dentures, teeth, denture reliners, fillings and miscellaneous uses. Plastics have been edging into the dental market for over a half century. Even before the introduction of acrylics to the dental profession in 1937, nitrocellulose, phenol-formaldehyde and vinyl plastics were used as denture base materials. Results, however, were not wholly satisfactory because these plastics did not have the proper requisites of dental plastics. Since then, PMMAs have kept their lead as the most useful dental plastics, although many new plastics have appeared and are still being tested. Predominance of PMMAs is not surprising, for they are reasonably strong, have exceptional optical properties, low water absorption and solubility, and excellent dimensional stability. Most denture base materials, therefore, contain PMMA as the main ingredient. 

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. 

Mixed plastics waste appears to be well suited for use in energy recovery, either as a co-eombustion fuel in a power plant designed for solid fuels, or as the sole fuel in speeially designed plants. This paper reports test results on the co-combustion of mixed household plasties with eoal. The tests were performed in a bubbling fluidised bed low-pressure steam boiler. The results show that both inorganic and organic total specific emissions were lower for mixed household plasties than for coal. Tabulated data are presented. 3 refs. 

Since the hardness test involves a substantial component of plastic deformation, hardness values are linked with tensile strength and not with yield strength when correlation between hardness and tensile properties are carried out. This appears to be a relationship between the hardness and tensile properties are carried out. There appears to be a relationship between he hardness of a metal and its tensile strength, but no general application has been found to exist. However, the following empirical relationship appears to hold fairly well for most steels, other than heavily cold worked steels or austenitic steels. 

To test the assumption whether additives indeed do not contribute to any significant amount to life cycle impacts of plastics, Van Oers and Van der Voet [1] conducted a case study on PVC flooring, appearing in this volume as well. They conclude that additives can indeed contribute to life cycle impacts, and therefore more attention should be paid to additives. Closing the data gaps therefore seems to be a very important issue. 

---