The excess energy approach to the impact testing of plastics

This paper evaluates the excess energy approach to impact testing of plastic samples. This approach assumes that providing the impact energy is excessive, the rate of strain during a test may be assumed to be constant. This allows a direct transformation of time to displacement during a test and consequently to a simplification of the integration procedure. The force-time and force-displacement responses of samples to impact have been measured simultaneously using an instrumented falling weight impact machine. It is concluded that the excess energy approach is acceptable providing the available impact energy exceeds the impact strength of the sample by a factor of ten.     

Microhardness testing of plastics

Microhardness measurements have been carried out on polymethyl methacrylate, unplasticised polyvinyl chloride, polypropylene and acetal coplymer using two different test methods. In one case the depth of penetration of a Vickers indenter is measured during application of the load and in the other case the size of the Vickers indent has been measured after removal of the load. It has been found that the microhardness value for a plastic is dependent on the indenter load and the time for which the load is applied. After load removal there is time-dependent recovery of the size of the indent although the vast majority of this occurs in the depth of the indent rather than the diagonals. From the results in these tests it has been possible to obtain an equation which predicts the microhardness value in each material for any combination of loading time and applied load.     

Multiaxial mechanical testing of plastics

This paper outlines the many problems associated with the testing of plastics and suggests a method of minimising these problems by the use of multiaxial testing techniques. It extends the multiaxial approach into the determination of the fatigue loading characteristics of a plastic. General design criteria of such machines, as well as details of a family of machines that have been developed for that purpose, are given.     

Requirements for physical testing of rubbers and plastics

This introductory paper reviews in a general way the requirements for physical testing of rubbers and plastics. The perennial questions of why and how we test are raised and considered with reference to product examples. A grouping of physical tests is suggested based on the use and value of the information they provide and related to the reasons for testing. Particular attention is given to the role of standards and to the sometimes conflicting requirements of quality control and design.     

Standardized methods of testing flammability of plastics

The paper is giving a survey of the most important standardized methods for testing flammability and relative parameters of plastics. The items described are dealing with the determination of flash point, heat resistance, burning behaviour. Some new drafts and projects of international standards are also mentioned.     

Impact testing of plastics: Present knowledge

This work takes a look at the present knowledge of the impact resistance of plastics. Two approaches are discussed and examined: the first is instrumented impact testing, and the second is that proposed by Williams and coworkers at Imperial College, London. The advantages of both are discussed and examined with particular reference to fracture mechanics analysis of impact data. It is shown that fracture mechanics gives a satisfactory theoretical assessment of the whole problem and many of the most important parameters of the material can now be determined by impact testing.     

Microhardness testing of plastics: Literature review

A review is presented of microhardness tests applicable to plastics. The methods are outlined and the effect of test variables considered. Published literature describing applications of microhardness measurements to plastics including structure and environmental resistance are reviewed.     

Compatibilization and impact modification of mixed recycled plastics

In order to solve the problems related to the reuse and recycling of polymer materials, approaches must be developed to address the incompatibility of most plastics. In many cases, the complete separation of dissimilar plastics may not be economically feasible or technologically possible, so commingled plastics recycling may be the only option. Our work has concentrated on upgrading the performance of a blend of two incompatible polymers. For this, we have used a model composition of two plastics commonly found in business machine housings. Our approach concentrates on compatibilization of the blend with a tailored copolymer, in addition to impact modification of the different phases. Improvements in mechanical performance of the blends are elucidated through the use of transmission electron microscopy.     

Microhardness testing of plastics using ball and conical indenters

A series of micro-indentation hardness tests have been carried out using both ball and conical indenters on polypropylene, unplasticised polyvinyl chloride and polymethyl methacrylate. It has been found that for the ball indenters the hardness number for each of the plastics increases as the applied load increases or as the ball diameter decreases. A simple empirical relationship has been developed which permits the hardness number of the plastics to be predicted for any combination of ball size and applied load.For the conical indenter it was found that the hardness number of each of the plastics decreases in a simple manner as the applied load increases but the overall relationship between hardness number and cone angle is complex.     

Brittle-tough transition temperatures in impact tests on rubber-toughened plastics

— In notched impact tests, rubber-toughened plastics show abrupt transitions in toughness with increasing temperature. Typically, there are two such transitions, one just above the T_g of the rubber phase, and the second some tens of degrees higher. The factors affecting the positions of these transitions are discussed. The relaxation behaviour of the rubber phase is a key factor, but rubber content and particle size are also important. Examples of impact transitions in high-impact polystyrene (HIPS) and toughened nylon are discussed.     

Interlaboratory comparison of melt flow rate testing of moisture sensitive plastics

The current standard for melt flow rate testing, ISO 1133, does not adequately cover the measurement of materials that degrade or further polymerise at the melt flow rate test conditions. Materials such as PET, PBT and PA tend to degrade, sometimes rapidly, at melt temperatures if they contain absorbed water. This results in poor repeatability and reproducibility of melt flow rate results. The ISO Plastics Melt Rheology Working Group (TC61/SC5/WG9) is currently developing a modified melt flow rate test method for reliable measurement of moisture sensitive materials, thereby providing an alternative to intrinsic viscosity measurements. The modified method controls more tightly the time–temperature history experienced by the material during testing and, thus, the resultant variability in measured properties due to degradation.The results of an intercomparison of testing of moisture sensitive polymers using the melt volume flow rate (MVR) and melt mass flow rate (MFR) methods are reported. A polypropylene (PP), used as a benchmark material, and five moisture sensitive materials were tested by a number of laboratories measuring either MVR or MFR, or both. For standard testing of the PP material, the repeatability and reproducibility of measurements of MVR were up to 5% and 11%, respectively, and for MFR were 7% and 21%, respectively (95% confidence level, outliers excluded). For the moisture sensitive materials the repeatability and reproducibility of measurements varied significantly, with repeatability values up to 26% and reproducibility values up to 114% being obtained. By imposing moisture and temperature control criteria in accordance with the proposed testing standard, the repeatability and reproducibility limits were significantly reduced to approximately 10% and 60%, respectively. The results suggest that both the moisture and temperature criteria were important for improving the repeatability of MVR measurements. However, the moisture content criterion was more important for improving the reproducibility of MVR measurements.The need to tightly control the sample preparation, in particular the drying and subsequent sample handing procedures, and the time–temperature history of the sample throughout the test is considered critical to further improve the precision of measurements of such materials.     

Instrumentation for neutron spectroscopy

The basic principles of operation of most types of neutron spectrometers used by chemists are reviewed. The merits and constraints of each type is explained in terms of energy range, resolution, data rate and momentum transfer range so that the reader can understand why particular experiments are, or are not, done.     

Instrumentation for capillary electrochromatography

One of the reasons for the immense interest in capillary electrochromatography (CEC) is its feature to combine chromatographic selectivity with the high efficiency and the miniaturization potential of capillary electrophoresis (CE). The capability of commercial CE instruments to run CEC has enforced the readiness of users and researchers to work on this separation technique. Nevertheless, to fully exploit the potential of CEC, a routine CE device can certainly not fulfill all requirements. Two different approaches have been made to overcome this problem. The first was to modify commercial CE instruments for various demands. Pressurization of the packed capillary to prevent "air" bubble formation, gradient elution capabilities and thermostating devices allowing a greater flexibility in column designs have been implemented in CE instruments of several manufacturers. A completely different approach is the development of modular laboratory-made instrumentation dedicated to special CEC requirements. In order to increase mobile phase velocity and thus the speed of analysis the availability of voltages higher than 30 kV was accomplished in some of these devices. Gradient elution was achieved by either coupling of gradient LC systems or an electroosmotic generation of the changing eluent composition. When a pressure gradient is applied between both column ends in addition to the voltage gradient, a hybrid between capillary HPLC and CEC results. This chromatographic mode is named pressure-assisted electrochromatography (PEC). Either CE instruments equipped with additional HPLC pumps or modular laboratory-made devices are suitable for PEC. In CEC, sensitivity for UV detection is rather poor due to the short optical path length for on-column detection in capillary separation techniques. A special cell design with enhanced light path is presented and further principles like, e.g., fluorescence detection and coupling to mass spectrometry are discussed.     

Instrumentation for capillary isotachophoresis

Modular instrumentation for capillary isotachophoresis provides an easy way to assemble a desirable configuration of the separation unit with respect to detection limits, load capacity, time and economy of analysis. New developments in the field may thus be quickly accepted.     

Instrumentation for luminescence methods of analysis

Reactions which produce light (bioluminescence and chemiluminescence) can be used to measure as little as a picogram (10^?12 g) of analyte, such as ATP, NADH and many organic and inorganic compounds. The light levels produced are extremely low and instruments with special features are required for their measurement.     

High-temperature glass-fiber-reinforced plastics for aeronautical products

The main types of both widely used and promising glass-fiber-reinforced plastics based on temperature- resistant binders that are efficient in a temperature range of 160–400°C are considered. Basic mechanical and dielectric properties of the developed glass-fiber-reinforced plastics are presented.