Dynamic mechanical properties of a TiO₂‐filled crosslinked epoxy resin from 20–90°C.

Abstract

synopsisDynamic mechanical measurements were made with a torsional pendulum of a TiOr filled epoxy polymer (crosslinked with hexamethylene diamine) over a temperature range from 2&90°C., at filler concentrations of 0-40 wt.-%. The second-order transition temperature (To) was raised as the filler content increased. The behavior of Ti02 filler results in a long-range i m m o b~a t i o n of the highly crosslinked system with resultant increases in shear modulus (higher G') as well as decreased capacity for energy dissipation (lower damping factor). The out-of-phase modulus (G") increased with filler content as well. The magnitudes of the slope parameters H, (representing GI data above To) and H, (representing G ' data below T,) decreased with greater filler content. The possibility is set forth that the Ti02 filler causes a different distribution of mobility around the nitrogen junction as well as a change in the effective number of CHS units between crosslinks. IntroductionA number of investigations have been made on the effect of filler on the physical properties of polymers. Increases were observed in the glass transition temperature (T,) of polyurethane and polyisobutylene which were fdled with glass beads.' Glass powder filled poly(methy1 methacrylate) and polystyrene also showed increases in T,.2 The ultimate tensile properties of these filled polymers can be represented by master curves with a WLF equation which is near universal function of the glass temperature.The increase in T, apparently depends on volume fraction of filler and could be due to the immobilization of polymer segments near the filler surface.a The change in T , when Ti02 was added to poly(viny1 chloride-acetate) copolymer was also indicated by the changes in temperature coefficients of gas diffusion through the polymer at Tn.4 Correspondingly, carbon blackfilled polyisobutylene, acrylonitrile rubber, and cis-polyb~tadiene~ did not exhibit changes in the glass transition temperature. ExperimentalDispersion of titanium dioxide (Rutile 610, DuPont Corp., average size 0.2 p ) in 4,4'-bisglycidylphenyl 2-2'-propane (EPON-828 from Shell Chemical Co.) was achieved with a three roll mill. Both TiOz-filled and un-1475 1476 GALPERIN filled and 4,4'-bisglycidylphenyl 2-2'-propane and 1,Ghexanediamine (m.p. 3941"C., Matheson, Coleman and Bell Co.) were mixed in stoichiometric amounts at the melting point of the diamine. The mixture was heated in molds at 60°C. for 24 hr. to prepare torsional pendulum specimens. After this, the samples were placed in a dessicator for at least 24 hr. before use. Ti02 filler levels used ranged from 0 4 0 wt.-%.Dynamic mechanical measurements were made with a torsional pendulum (Plas-Tech. Corp.) employing a linear differential transformer coupled to a high-speed recorder (Sanborn No. 296). Sample size ranged from 25 to 35 mil thickness. Temperatures employed were from 20 to 90" C. Results and DiscussionThis is shown in Figure 1 where A is plotted against the amount of Ti02 filler present for different temperatures from 20...

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