Plastics test conditions

The radiation and temperature dependent mechanical properties of viscoelastic materials (modulus and loss) are of great interest throughout the plastics, polymer, and rubber from initial design to routine production. There are a number of laboratory research instruments are available to determine these properties. All these hardness tests conducted on polymeric materials involve the penetration of the sample under consideration by loaded spheres or other geometric shapes [1]. Most of these tests are to some extent arbitrary because the penetration of an indenter into viscoelastic material increases with time. For example, standard durometer test (the "Shore A") is widely used to measure the static "hardness" or resistance to indentation. However, it does not measure basic material properties, and its results depend on the specimen geometry (it is difficult to make available the identity of the initial position of the devices on cylinder or spherical surfaces while measuring) and test conditions, and some arbitrary time must be selected to compare different materials. 

Toxicity. The products of combustioa have beea studied for a number of plastic foams (257). As with other organics the primary products of combustion are most often carbon monoxide and carbon dioxide with smaller amounts of many other species depending on product composition and test conditions. 

Fig. 2. Schematic of energy dissipation in a commonly used peel test. The energy dissipation can occur in the adhesive and/or the adherends. The extent of energy dissipation depends on the elasto-plastic properties of the adhesive and the adherends under the test conditions as well as the local stresses and strains near the crack tip.

Flammability. The fire hazard associated with plastics has always been difficult to assess and numerous tests have been devised which attempt to grade materials as regards flammability by standard small scale methods under controlled but necessarily artificial conditions. Descriptions of plastics as selfextinguishing, slow burning, fire retardant etc. have been employed to describe their behaviour under such standard test conditions, but could never be regarded as predictions of the performance of the material in real fire situations, the nature and scale of which can vary so much. 

Fig. 2.80 is typical of the effects which may be observed with several common plastics materials. C ite apart from the changes in impact strength with temperature an important lesson which should be learned from this diagram is that the ranking of the materials is once again influenced by the test conditions. For example, at 20°C polypropylene is superior to acetal whereas at — 20°C it... 

It is important for the designer to become familiar with all the information that is available for each plastic, especially that which is pertinent to the product design requirements. Designers, who are knowledgeable of the data derived from metal tests, could have a tendency to apply the plastic data sheet information in a manner similar to that used for metals. This could be understood because there is no warning that some of the data supplied by the manufacturer are applicable only when use and test conditions are nearly the same. 

Creep modeling A stress-strain diagram is a significant source of data for a material. In metals, for example, most of the needed data for mechanical property considerations are obtained from a stress-strain diagram. In plastic, however, the viscoelasticity causes an initial deformation at a specific load and temperature and is followed by a continuous increase in strain under identical test conditions until the product is either dimensionally out of tolerance or fails in rupture as a result of excessive deformation. This type of an occurrence can be explained with the aid of the Maxwell model shown in Fig. 2-24. 

The reaction of plastics under test conditions to their behaviors is explained in other Chapters, particularly Chapters 2,5 to 7. Until this phase of the information is properly understood, it is best not to apply the numbers from the data sheet, for they can be a source of misinterpreted information. A con-... 

The difference in thermal expansion between the usual commodity plastics and steel is very large. It is to be noted that some plastic material changes in length rather abruptly at some temperatures, beyond the limits of the test condition. In such cases, a special investigation should be instigated, and the coefficient of expansion established under temperatures of usage. However there are plastics that can be compounded to match or even have less thermal expansion than steel, etc. 

This article outlines the food contact legislation in the UK that applies to plastic articles and materials that come into contact with food. Key requirements are that materials must not transfer chemicals to food in quantities that cause a hazard to human health, or cause the food to become tainted with a strange taste or odour. The regulations also set out testing conditions that enable compliance with the requirements to be demonstrated. 

The mechanism and hence the rate of wear can change, sometimes quite suddenly, with conditions such as contact pressure, speed and temperature. In any practical circumstance the mechanisms may be complex and critically dependent on the conditions. Consequently, the critical factor as regards testing is that the test conditions must essentially reproduce the service conditions if a good correlation is to be obtained. Even a comparison between two plastics may be invalid if the dominant mechanism is different in test and service. 

It follows that there cannot be a universal standard abrasion test method for plastics and the test method and test conditions have to be chosen to suit the end application. Also, great care has to be taken if the test is intended to provide a significant degree of acceleration. 

ISO 527-4, Plastics - Determination of tensile properties - Part 4 Test conditions for isotropic and orthotropic fibre-reinforced plastic composites, 1997. 

For details of the test methods used to measure physical properties reference is made to Handbook of Plastics Test Methods or the more recent Handbook of Polymer Testing [2, 3]. Standard tests have their limitations most were intended for quality control rather than prediction of service performance and produce arbitrary rather than fundamental measures of the properties. They do have the advantages of making data compatible with others and often have known reproducibility. In many standard methods the user is encouraged to opt for standard or preferred conditions which may not have relevance to the service conditions of the product. It is then sensible to base the testing on standard methods but to use more relevant conditions of, for example, time, temperature or stress. 

ISO 527-4 1997 Plastics - Determination of tensile properties - Part 4 Test conditions for isotropic and orthotropic fibre-reinforced plastic composites ISO 527-5 1997 Plastics - Determination of tensile properties - Part 5 Test conditions for unidirectional fibre-reinforced plastic composites ISO 1798 1997 Flexible cellular polymeric materials - Determination of tensile strength and elongation at break... 

ISO 4433-4 1997 Thermoplastics pipes - Resistance to liquid chemicals - Classification -Part 4 Poly(vinylidene fluoride) (PVDF) pipes ISO 9393-2 1997 Thermoplastics valves - Pressure test methods and requirements - Part 2 Test conditions and basic requirements for PE, PP, PVC-U and PVDF valves ISO 10931-1 1997 Plastics piping systems for industrial applications - Poly(vinylidene fluoride) (PVDF) - Part 1 General... 

Zeolite/polymer mixed-matrix membranes prepared from crosslinked polymers and surface-modified zeolite particles offered both outstanding separation properties and swelling resistance for some gas and vapor separations such as purification of natural gas. Hillock and coworkers reported that crosslinked mixed-matrix membranes prepared from modified SSZ-13 zeolite and 1,3-propane diol crosslinked polyimide (6FDA-DAM-DABA) synthesized from 2,2 -feis-(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, p-dimethylaminobenzylamine-and 3,5-diaminobenzoic acid displayed high CO2/CH4 selectivities of up to 47 Barrer and CO2 permeabilities of up to 89 Barrer under mixed gas testing conditions [71]. Additionally, these crosslinked mixed-matrix membranes were resistant to CO2 plasticization up to 450 psia (3100kPa). 

It is always very useful to be able to predict at what level of external stress and in which directions the macroscopic yielding will occur under different loading geometry. Mathematically, the aim is to find functions of all stress components which reach their critical values equal to some material properties for all different test geometries. This is mathematically equivalent to derivation of some plastic instability conditions commonly termed as the yield criterion. Historically, the yield criteria derived for metals were appHed to polymers and, later, these criteria have been modified as the knowledge of the differences in deformation behavior of polymers compared to metals has been acquired [20,25,114,115]. 

In a few cases, a guide to testing for a particular property already exists, for example the international standard for dynamic properties3. The logic here was that there are many different forms of apparatus in use, and no general consensus on a single set of test conditions, so that the alternative would be a whole series of different standards (a route taken by the plastics industry). 

As it was recognized that the number of variations included in many test method standards was not helpful in respect of obtaining input for databases, there was an initiative in the plastics industry that produced international standards for acquisition and presentation of single and multipoint data. These specify the particular test methods and test conditions to produce strictly comparable data. Very recently, this approach has been taken up in ISO TC 45 and drafts circulated based on British standards4, 5. These standards are not explicit about including thermoplastic elastomers and, as discussed in Chapter 2, Section 9, an acquisition standard for these materials has been proposed in ISO TC 61, Plastics. An example of the problems resulting from lack of consensus on test methods was evident for EPDM polymers and the results of collaboration to rectify this have been published6. 

It is clear that to get an accurate idea of how a rubber behaves in the nip of a mill or the die of an extruder is a difficult problem which has not been solved by the traditional plasticity tests. Hence, these tests have mostly been used as a check on the uniformity of repeat batches. As Figure 6.1 shows, even this may not be satisfactory as no difference in behaviour under the test conditions does not mean that there is not a difference under processing conditions. Fortunately, in practice repeat batches of basically very similar materials do not yield intersecting flow curves. It becomes clear that to obtain improved correlation with processing behaviour in service it is necessary to use tests which involve increased shear rates and/or consideration of the elastic as well as the plastic component of stress. 

In a separate experiment, two regions of rat brain tissue sections that contained different levels of clozapine based on the MALDI-IMS results were isolated. The isolated tissue sections were transferred into plastic test tubes and mixed with 300 p,L of 95 5 methanol-water solution for protein precipitation. After centrifugation, a 10-p.L aliquot of the supernatant from each sample was injected for HPLC-MS/MS analysis. The HPLC was operated under a fast gradient condition using a cyano... 

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