Stress relaxation of paper plastic composites
Fractional stress relaxation ( S(t)/S(0.04 ) ) was used to compare time-dependent properties of papers, plastics and paper plastic composites ( PPC ). No similar observations appear in the literature. Laboratory handsheets were prepared from commercial western hemlock ( Tsuga heterophylla (Raf.) Sarg. ) unbrightened and brightened groundwoods, as well as unbleached and bleached kraft pulps. Adjustments were made to provide equivalent basis weights ( 150 ± 30 g/m² ) for materials of the study.
... als of the study. Handsheets were impregnated with methyl methacrylate ( MMA ) and tetraethylene glycol dimethacrylate ( TEGDMA ) (co)monomer systems. Saturated handsheets and plastic films were cured by ⁶⁰Co gamma irradiation ( 1.4 ± 0.9 Mrad ). It was found that the standard log-time equation, S(t)/S(0.04) = a + b ln t, applied to data collected between 0.04 and 35 min following completion of simulated step-loading ( r ² mostly 0.97 or higher ). A second quantity, energy dissipation ( ΔS), ΔS = 1 - S(35)/S(0.04), was used to compare between treatments. Some plastics gave the highest ΔS values, while groundwoods gave lowest values and kraft papers were intermediate. Pulp delignification level appeared to relate directly to ΔS. Within limits of the study it seems that PPC stress relaxation curves were influenced by both polymer ( matrix ) and fibre ( substrate ) employed. The former contributed in minor ways, while the latter operated in major ways.