Phenolics Thermomechanical analysis

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

Thermomechanical analysis (TMA) is the measurement of the deformation of the phenolic material imder a constant strain as a function of temperature or time. TM A invesfigalion of crosslinked, modified phenolics gives the linear expansion coefficient and the glass tiansifion temperature of this material [33]. The linear expansion coefficient ( ) is measured by thermal expansion in one dimension. It is defined by equation 62 where dL/dT is the slope of the jdot of the longest sample dimension versus sample temperature and L is the original length of the crosslinked phenolic sample. 

The heat distortion temperature at 1.80 Mpa is the temperature that causes a beam loaded to 1.80 to deflect by 0.3 mm. If the heat distortion temperature is lower than the ambient temperature, -20 C is given. Polymers such as low-density polyethylene, styrene ethylene-butene terpolymer, ethylene-vinyl acetate copolymer, polyurethane, and plasticized polyvinyl chloride distort at temperatures below <50°C, whereas others, such as epoxies, polyether ether ketone, polydiallylphthalate, polydiallyl isophthalate, polycarbonate, alkyd resins, phenol formaldehyde, polymide 6,10 polyimide, poly-etherimides, polyphenylene sulfide, polyethersulfone, polysulfonates, and silicones, have remaikably high distortion temperatures in the range of 150°C to >300 C. Thermomechanical analysis has been used to determine the deflection temperature of polymers and sample loading forces (i.e., plots of temperature vs. flexure). 

Thermomechanical analysis (TMA) was used to investigate the curing behavior of resorcinol-formaldehyde (RF) and phenol-resorcinol-formaldheyde (PRF) adhesive resins used for structural glued laminated timber and veneer lumber, Samples were heated from room temperature... 

High temperature thermomechanical behavior of carbon-phenolic and carbon-carbon composites, I. Analysis. J. Compos. Mater., 26 (2), 206-229. 

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