The coefficient of dynamic friction is often the controlling factor for solids conveying, pressure generation, and thermal decomposition of a resin in the feed section of a single‐screw plasticating extruder. The coefficients of friction are, however, very poorly understood, and the interpretation of the measurements are complicated by the dissipation of frictional energy at the sliding interface. A new instrument was recently built to help understand dynamic friction, and a numerical technique was developed to estimate the interface temperature. The coefficients of dynamic friction for a low‐density polyethylene resin are presented in this paper as a function of the surface temperature, pressure, and velocity.
Differential scanning calorimetry is used to analyze the phase transitions of various heat‐treated poly(p‐xylylene)s, polymerized from 78 to 296 K. The data were extrapolated, as needed, to completely amorphous or completely crystalline polymer. The glass transition was found to be at 286 K; the increase in heat capacity at the glass transition is 37,6 J · K−1 · mol−1. The crystals of the α polymorph change at 504 K to the β1 polymorph (enthalpy of transition of 5,0 kJ · mol−1), then, at 560 K to the β2 polymorph (enthalpy of transition of 1,5 kJ · mol−1), and finally at 700 K to the isotropic melt (heat of transition of 10,0 kJ · mol−1). Both the β1 and β2 polymorphs are assumed to be conformationally disordered (condis crystals). The reversibility of the transitions, annealing peaks, crystallization on heating, abnormally high heat capacities of β1 crystals, and abnormally low heat capacities of α crystals are discussed.
New epoxy‐based thermoplastics for barrier packaging are discussed here (see Figure). The polymers, poly (hydroxyaminoethers), are typically generated through reactions of various dinucleophiles with epoxy monomers. The effects of functionalization, branching, and copolymerization on the mechanical, adhesive, and barrier properties of these resins are reviewed.
SynopsisThe constant-pressure heat capacity C, of poly(p-xylylene) (PPX) has been measured from 220 to 625 K by differential scanning calorimetry. The constant-volume heat capacities C, of both, PPX and its isomer polystyrene (PS) have been interpret4 in the light of literature data on full normal-mode calculations for PS and estimates from low-molecular-weight analogs for PPX for the 39 group vibrations. Nine skeletal vibrations were used in this discussion with characteristic temperatures 0, and 0, of 534.5 and 43.1 K for PS. It was also possible to calculate a heat capacity contribution of a phenylene group within a polymer chain. Single 48-vibration 0, temperatures of 3230 K for PS and 2960 K for PPX are sufficient to describe C , above 220 K. Below 140 K, PS heat capacity shows deviations from the Tarasov treatment.'Present affiliation: The Dow Chemical Company, Midland, MI 48640.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.