Anionic copolymers of octanelactam with laurolactam (nylon 8/12 copolymers)—v. Effect of annealing on thermal properties and crystalline structure

The effects of different annealing time/temperature regimes on the thermal and crystalline behaviour of a series of statistical copolyamides (nylon 8/nylon 12), prepared by activated anionic polymerization of octanelactam/laurolactam (OL/LL), were determined by DSC, X-ray (WAXS), density and viscosity measurements. The melting temperature and the heat of melting increased with annealing time and temperature. The results were correlated with the molar composition of the copolyamides and showed a gradual increase in percentage crystallinity with time.     

Anionic copolymers of octanelactam with laurolactam (nylon-8/12)—IV. Dynamic thermomechanical and mechanical properties

The thermomechanical and the mechanical properties of a recent series of copolyamides of octanelactam (OL) and laurolactam (LL) (nylon-8/nylon-12) were studied. The glass transition temperature (T_g) and melting point (T_m) were determined with dynamic mechanical thermal analyser, and compared to those obtained with differential scanning calorimetry and the activation energy for glass transition was calculated. The copolyamides showed a minimum for tensile strength, yield stress, stress at 100% and modulus and a maximum for elongation at break at the composition 60/40 (OL/LL) which has the lowest crystallinity. Young's modulus against % elongation showed the classification of copolyamides in two groups (rich in OL or LL, respectively).     

Diffusion and permeation of gases in undrawn and radially drawn films of native and commercial gutta-percha (trans-Polyisoprene)

The permeability of native and commercial grades of gutta-percha (trans-polyisoprene), was determined and related to diffusion rate both below and above the glass transition temperature (T_g) and the melting point (T_m). Both radially drawn and undrawn membranes were evaluated. Five gases (O₂, N₂, CO₂, H₂ and He) were used as permeants and the measurements were taken both above and below the polymers' crystalline T_m. The diffusivity of the gases was found to have an increased rate above the T_m. The reduction of solubility, diffusivity and permeability with increasing draw ratio was attributed to an increase in crystallinity.