Pressure-volume-temperature relations of a poly-epsilon-caprolactam and its nanocomposite

The equation of state of a poly-E-caprolactam melt, PA-6, of molar mass M-n = 22kg/mol was investigated in a Gnomix apparatus (Gnomix Inc., Boulder, C olorado) between 300 and 560 K, and pressures up to 150 MPa. Cot-responding measurements were performed with addition of 1.6 wt% of montmorillonite ex foliated particles. Reductions in specific volume of about 1.0 and 1.4%, re spectively, at 10 and 150 MPa, are observed. For the melt, excellent agreem ent between experiment and the results from lattice-hole theory is found fo r both systems. Addition of the nanoparticles reduced the hole (free volume ) fraction by 14%. Evidently, the hole fraction is a sensitive indicator of structural changes. It is noteworthy that such a small quantity of added n anoparticles increases the tensile strength by about 14% and modulus by 26% , at a cost of reduction in the elongation at break by about 25%. For a treatment of the PNC, and as an approximation, our earlier model of a particulate composite was adopted. To calculate the binary interaction par ameters it was assumed that: (1) the clay particles are in form of flat dis ks, 100 nm diameter and 1 nm thick; (2) the hard core segments of polymer a nd of solid occupy the same lattice volume, i.e. v(11)(*) = v(22)(*); (3) t he energetic interactions of polymer with solid are given by the geometric average between the two self-interactions. These assumptions lead to the fo llowing results ('11' represents polymer-polymer, '22' represents clay-clay and '12' represents polymer-clay interactions): epsilon (*)(11) = 32.09; epsilon (*)(12) = 313.54 and epsilon (*)(22) = 306 3 (kJ/mol) upsilon (*)(17) = 24.89; upsilon (*)(12) = 33.53 and upsilon (*)(22) = 24.8 9 (ml/mol).