J. M. De Bruijn

Role of oxygen diffusion in polymer ageing: kinetic and mechanical aspects

For an ageing process involving the consumption of a small molecule (typically O2 or H2O) by reaction with the polymer, there are critical conditions of reaction rate and/or thickness above which the process becomes kinetically controlled by the diffusion of the small molecule in the polymer. Suitable lifetime prediction models must then involve the thickness distribution of reaction products. This latter can be predicted from Ficks law, modified by a term relative to the rate of consumption of the diffusing species by the chemical reaction. Some problems related to the use of this approach are examined here. It appears that, in the most frequent case, the thickness of the degraded layer is of the order of magnitude of D/k, where D is the diffusion coefficient and k the pseudo-first-order rate constant for reactant consumption. Some examples of application related to photochemical, radiochemical and thermochemical ageing are examined. It can, for instance, be shown that in photochemical or radiochemical ageing, the thickness of the oxidized layer (TOL) is proportional to the reciprocal of lβ, where l is the radiation intensity and Β an exponent depending essentially on the radical chain mechanism. It is generally expected that in the case of thermal ageing, the TOL is a decreasing function of the temperature. Some consequences of diffusion control on accelerated and natural ageing methods are briefly examined. The consequences of the ageing-induced “skin-core” structure due to the diffusion control are examined. The main features of the observed polymer embrittlement can be explained in terms of fracture mechanics.

Integrated smart two-dimensional thermal flow sensor with Seebeck-voltage-to-frequency conversion

Abstract A smart sensor has been developed for the measurements of both flow direction and velocity. The sensor uses a thermal principle, which allows complete integration together with electronic circuitry on one chip. A groove is etched to create thermal isolation between the sensor and the chip edge to obtain an essential variable (the flow temperature). On the edge a voltage-to-frequency (V/f) converter is placed as a first step towards a digital output. The V/f converter is able to convert voltages in the range of 1 μV to 1 mV. The frequency output signal is a direct measure for the wind velocity. The presence of a multiplexer enables direction measurement and calibration of the sensor.

Alkaline Degradation of Monosaccharides VI1: The Fhucto-Fobmose Reaction of Mixtures of D-Fructose and Formaldehyde

Abstract The final product compositions of the alkaline (calcium hydroxide) degradation of D-fructose in the presence of formaldehyde at several D-fructose/formaldehyde ratios, and of the formose reaction were determined by HPLC and GC analysis. At decreasing D-fructose/formaldehyde ratio a gradual change of the composition was observed except for lactic acid and the oligomeric acidic products, which show a minimum and a maximum, respectively. A mechanistic explanation is given by the aldolization of formaldehyde both with saccharides and with their subsequent α-dicarbonyl intermediates, which favours the formation of oligomeric products at the cost of lactic acid. It is established both experimentally and theoretically that there is no essential mechanistic difference between the formose reaction and the alkaline degradation of monosaccharides.

The design and application of a microfoil tensile test apparatus for monitoring the degree of ultraviolet degradation of polymers

A microfoil tensile test apparatus has been developed to determine the tensile strength of thin slices cut from the surface of uv‐degraded plastic products. It will be shown that it is possible to obtain data on the degree and depth of ultraviolet degradation in polypropylene copolymer and high‐density polyethylene with the microfoil tensile test apparatus and to relate this to the impact resistance. The results are in agreement with the results determined by infrared spectroscopy but are obtained in less time and more accurately. The influences of sample preparation and geometry, elapsed time after microtoming, and method of processing on the tensile strength, will be discussed.

Integrated sensor for non-invasive monitoring of flow in pipes

A silicon chip fabricated with standard IC technology has been used to monitor air flow in a pipe in a non-invasive way through the pipe wall. Flow detection is based on the measurement of a temperature difference on the chip, which is heated with respect to the flow. The device is direction sensitive and has a zero output in the absence of flow. In the experiment the detection threshold for air flow is approximately 0.1 m/s.