Investigation of dielectric properties of bacterial cellulose -thermoset resin nanobiocomposite

Cellulose is the most abundant polymer on earth and has enormous industrial importance.one of the common applications for native cellulose is using as electrical insulator. The main hurdle of cellulose as application in electrical insulators is porosity and hygroscopicity of paper. Thus to remove humidiy from pores, paper is impregnated by oil or resins. The aim of this research is using of bacteria to produce cellulose and preparation insulator composite and paper from bacterial cellulose. The other purpose is comparison physical properties them with composite and paper produced from kraft pulp.
Material and The organism used was Gluconacetobacter xylinus (BPR 2004) which was purchased from IROST, Iran. Kraft pulp was prepared from factory of Mazandaran wood and paper. G.xylinus was incubated in a static Hestrin-Schramm culture at 28°c For 30 days. The obtained BC pellicles had 10mm thick.Then, BC pellicles purified and washed by deionized water .The pellicles were cut into small pieces and disintegrated by blender and standard pulp-disintegrator in lab. Aqueous suspension of kraft pulp was prepared. The content of bacterial cellulose that was added to suspension, was as follows: %5, 10 % and 15%. To prepare hand sheets of kraft pulp and kraft pulp- BC was used from hand sheet maker. BC sheets prepared from disintegrated BC by vacuum method. The handsheets were dried in oven then conditioned. Basis weight of hand sheets was considered 60g/m2. Dried handsheets were immersed in phenolic resin (PF). To obtain composites, 5 immersed handsheets from every treatment lay up and hot pressed at 150 °c and 100Mpa for 10min. Then obtained samples conditioned.
Findings:To investigate of physical properties of samples was used from Dp, XRD ,FTIR,FE-SEM tests and also insulation tests composed of Loss tangent,capacitance,dielectric constant and break down voltage was used.The result showed degree of polymerization (Dp) bacterial cellulose was upper than kraft pulp.The result of X-ray diffraction indicated, crystallinity and crystalline size of bacterial cellulose was upper that kraft pulp. Air penetration test in hand sheets demonstrate with increasing bacterial cellulose decrease porosity and the air couldn’t penetrate in handsheet. Kraft paper showed most air penetration and also most porosity. FE-SEM images showed morphology and structure of samples. Findings of FTIR demonstrate interaction between reinforcement and matrix in composites. Dielectric properties was measured as loss tangent, capacitance, dielectric constant and breakdown voltage. The results showed BC and kraft paper had minimum and maximum loss tangent in order and this is conversely in its composite. With increasing of bacterial cellulose from 5-15%, loss tangent increased in hand sheets and its composites. Capacitance and dielectric constant showed similar trend to loss tangent. The breakdown voltage of hand sheets and composites increased with enhancement of bacterial cellulose.
The results showed ,crystallinity, crystal size and degree of polymerization of bacterial cellulose was upper than kraft pulp. Also hand sheets of bacterial cellulose had lower dielectric loss factor, dielectric constant, capacitance.But dielectric break down voltage ofbacterial cellulose handsheets was upper.