Short-Term Temperature Influence

Behavior under short-term temperature influence is usually characterized by determining the mechanical properties as functions of temperature. In order to evaluate behavior at higher temperatures, tensile strength and Young s modulus are often used, whereas impact and Charpy impact strength are often utilized for low-temperature behavior. 

Behavior under short-term temperature exposure is generally characterized hy mechanical properties as a function of temperature (heat distortion temperature, see Section 2.4.1). Long-term temperature influence is seen in chemical aging processes leading to crosslinking, cyclization, thermal-oxidative degradation, and others. 

Regarding the operational use of thermoplastics, we generally have to distinguish between short-term and long-term temperature influence, respectively. 

Rearrangements of halohydrin salts usually require prolonged treatment of ether solutions at ambient temperature or heating in a less polar solvent, but there are some interesting exceptions. The standard conditions consist of formation of the magnesiohalide salt in ether, followed by solvent replacement by benzene and short term reflux. House found that residual ether can significantly influence the course of a reaction, and since this variable appears not to have been carefully controlled in most experiments, comparisons may have limited significance. 

The purpose of this study was to evaluate laboratory formaldehyde release test methods for predicting real-life formaldehyde air concentrations human exposure levels, and health risk. Three test methods were investigated the European perforator test, the gas analysis method at 60 C and 3% RH, and the gas analysis method at 23 C and 55% RH. Different types of particleboard bonded with urea-formaldehyde and urea-melamine-formaldehyde resins were tested. The results were used to rank boards as a function of test method, conditioning, short-term humidity, and temperature variations during storage. Additional experiments were conducted in small experimental houses at a Dutch research institute. Our conclusions are that relative ranking of products is influenced by the test method and by change in relative humidity. The relationship between test method and release in real-life situations is not clear. In fact, it seems impossible to use laboratory measurements to predict real-life product performance of board if the board is not fully in equilibrium with the atmosphere. 

Application of fire-resistant coatings is one of the basic methods of protecting wood and other flammable materials from the influence of a fire and increased temperature. It is desirable to impart both short-term protection, to allow evacuation from a building, and long-term protection, to protect the surfaces from heat and fire damage and to prevent combustion. In recognition of the foregoing, various compositions have been developed that can add fire-retardant (-resistant) performance to substrates. 

Since vitamin D predominates over prevltamln D (8) In the equilibrium (ratio at 20°C v< 90/10) and has a considerable extinction coefficient (emax 19,500), Its presence decisively Influences the photochemistry occurring In the system at temperatures between 0 and 100°C. The photoreactions of vitamin D will be discussed In detail in Section V. Here we like to mention the curious fact that under the usual conditions the 5E-Isomer ("trans-vltamln D") (9, 10) Is not found in the Irradiation mixtures (11a). It Is formed from primary Irradiation products through a thermal Isomerization (cf. ref. 11a and Section V). Mermet-Bouvler reports the occurrence of trans-vltamln D In mixtures obtained after short-term Irradiation of vitamin D2 solution (12). 

The torsional vibration test according to DIN 53445 is used to investigate temperature-dependent viscoelastic material behavior. This is a short-term test. The time-to-mpture test according to DIN 53444 registers the influence of stress duration, stress type, and temperature. The torsional vibration test provides additional information on the damping behavior of the plastics tested (mechanical loss or damping factor d). Fig. 13 [9]. 

Table 4.40 Influence of temperature on short term flexural strength retention of FRP laminates, fabricated from several types of polyester resin (typical).

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