C. K. S. Pillai

Melt/solution processable conducting polyaniline with novel sulfonic acid dopants and its thermoplastic blends

Abstract The effects of three sulfonic acid dopants, sulfonic acid of 3-pentadecylphenol (SPDP), sulfonic acid of 3-pentadecylanisole (SPDA) and sulfonic acid of 3-pentadecylphenoxy acetic acid (SPDPAA) (synthesized from an inexpensive naturally existing biomonomer, cardanol) on the electrical conductivity and other properties of polyaniline (PANI) were studied. All the three dopants were found to act as very good plasticizing cum protonating agents for PANI. Doping was carried out either by the in situ doping emulsion polymerization route or by mechanical mixing of emeraldine base and the dopant. The protonated complexes obtained by the emulsion polymerisation route exhibited exceptionally high degree of crystalline order and orientation. Highly conducting free-standing films of protonated PANI could be prepared both by the solution casting and by the melt processing techniques. On thermal processing, free-standing flexible films with conductivities as high as 65 S cm −1 could be prepared. PANI protonated with the dopants, SPDA and SPDPAA were blended with poly(vinyl chloride) (PVC) and thin films were prepared by melt processing techniques and the properties of the blends were studied. Percolation threshold is occurring at very low weight percentage of PANI and a maximum coductivity value of 2.5 S cm −1 was obtained for 25 wt.% of PANI for PANI–SPDA–PVC system.

Melt/solution processable conducting polyaniline: doping studies with a novel phosphoric acid ester

Abstract Polyaniline (PANI) was doped with a novel dopant, 3-pentadecylphenylphosphoric acid (PDPPA), having a long hydrophobic hydrocarbon side chain, either by mechanical mixing of emeraldine base and PDPPA or by the emulsion polymerization route using xylene or chloroform as the solvent. The resulting PANI–PDPPA complexes obtained were characterised by FTIR, UV–Vis, conductivity measurements, XRD, SEM, DSC, TGA and polarised light microscopy. The formation of the complex induces solubility of PANI in commonly used weakly polar or non-polar organic solvents such as xylene, THF, chloroform, etc. Protonation gives a plasticized PANI–PDPPA complex which can be processed by both thermal and solution techniques. On thermal processing, a free-standing flexible film with conductivities of the order 1.8 S cm −1 was obtained.

Thermal degradation characteristics of natural rubber vulcanizates modified with phosphorylated cashew nut shell liquid

Abstract The thermal and thermo-oxidative decomposition characteristics of Natural Rubber (NR) vulcanizates modified with Phosphorylated Cashew Nut Shell Liquid (PCNSL) have been studied by Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Differential Thermal Analysis (DTA). The PCNSL modified NR vulcanizate showed improved thermal stability in air, compared to that in nitrogen, which is presumed to be due to the formation of intermediate thermally stable structures in the former. The kinetic parameters for the initial stage of degradation in air and in nitrogen have been evaluated by the Freeman-Carroll method. The higher value for activation energy for thermo-oxidative degradation of PCNSL modified NR (15.10kCal/mol) and Integral Procedural Decomposition Temperature, IPDT (366 °C). as against that for unmodified NR (13.04 kCal/mol and 347 °C, respectively) indicate the improved thermal stability of the rubber.

Vulcanization of natural rubber modified with cashew nut shell liquid and its phosphorylated derivative: a comparative study

Abstract The vulcanization characteristics of unfilled natural rubber (NR) compounds was studied in presence and absence of cashew nut shell liquid (CNSL) and its phosphorylated derivative (PCNSL) by using an oscillating disc rheometer at various temperatures. The case of crosslinking in the presence of PCNSL and the active role of PCNSL in the crosslinking reaction was shown by the comparatively higher values of the cure rate index and lower values of the activation energy of vulcanization.

Synthesis of novel liquid crystalline polymers with cross-linked network structures

Abstract Liquid crystalline (LC) polymers with cross-linked network structures containing azobenzene mesogens were synthesised from cardanol, the unsaturated C15 hydrocarbon side chain of which is utilised for cross-linking reactions. The azobenzene group was introduced by the diazo coupling reaction between cardanol and 4-aminobenzoic acid. The resulting monomer, 4-[(4-cardanyl)azo]benzoic acid (I) was polymerised by self-polycondensation using thionyl chloride and pyridine to get poly[4-[(4-cardanyl)azo]benzoic acid] (III). (I) was also converted to poly[4-[(4-acryloyloxycardanyl)azo]benzoic acid](IV) through acryloylation of (I) followed by free radical polymerisation. Cationic polymerisation of (I) gave poly {4-[(4-cardanyl)azo]benzoic acid} (V). The monomers and polymers were characterised using elemental analysis, IR, 1H and 13C NMR and UV–visible spectroscopy. Polymer (III) was neither soluble in any solvent nor fusible. Polymer (IV) was also insoluble, but swelling was observed with many solvents and polymer (V) was soluble in polar solvents. On slow heating, polymers IV and V also got converted to totally insoluble products. IR spectra indicated involvement of side chain unsaturation in bond formation leading to cross-linking. Threaded nematic textures were obtained when polymer (III) was heated to below 200°C and rapidly quenched to room temperatures and observed under PLM. Otherwise, on heating polymer (III) started decomposing near 200°C as observed by an exotherm in DSC and confirmed by TGA. Polymers (IV) and (V) exhibited schlieren nematic textures under PLM. Polymer (V) gave cross-linked transparent film when cast from a solvent and cured by slow heating.

Processability characteristics and physico-mechanical properties of natural rubber modified with cashewnut shell liquid and cashewnut shell liquid–formaldehyde resin

Abstract Natural rubber (NR) has been modified with 5–15 phr each of cashewnut shell liquid (CNSL) and cashewnut shell liquid–formaldehyde (CNSLF) resin with a view to studying the processability characteristics of the mixes and physicomechanical properties of their vulcanizates. The plasticizing effect of these additives in NR was shown by the reduction in melt viscosity and power consumption during mixing in a Brabender Plasticorder compared to that of unmodified NR. Despite the reduction in chemical crosslink density, the vulcanizates containing 15 phr of CNSL and 5–10 phr of CNSLF showed higher tensile and tear strengths and elongation at break. The higher values of activation energy for thermal decomposition of the vulcanizates containing 15 phr each of CNSL (301 kJ/mol) and CNSLF (372 kJ/mol) than that of the unmodified NR vulcanizate (177 kJ/mol) indicate improvement in thermal stability of NR vulcanizates in presence of the modifiers.

Processability characteristics and physico‐mechanical properties of natural rubber modified with rubber seed oil and epoxidized rubber seed oil

The processability characteristics and physico-mechanical properties of natural rubber (NR) modified with raw rubber seed oil and epoxidized rubber seed oil have been studied. The modified mixes showed higher scorch time and lower cure rate, crosslink density, and ultimate state of cure compared to an unmodified mix. The thermal stability of the vulcanizates was practically unaffected by the modification.

Lyotropic behaviour of liquid crystalline poly(ester amide) containing diamide links

Abstract The lyotropic behaviour of a poly(ester amide) (PEA), poly[bis (terephthalate butyramide) hexane] (PBTBH) containing aliphatic diamide links prepared through the amido diol route was studied by isothermal viscosity measurements at different shear rates and cross polarized light microscopic measurements in m-cresol, N-methyl pyrollidone (NMP) and concentrated sulphuric acid. The effects of polarity of solvent, shear rate and polydispersity on the threshold concentration were investigated. The viscosity values of the liquid crystalline (l.c.) PEA were found to increase with increase in concentration, reach a maximum and then decrease sharply. The critical concentration at which the viscosity–concentration curve shows a maximum and the threshold concentration where maximum anisotropy was observed did not coincide. The threshold concentrations in the viscosity-concentration curve obtained for the PEA are 56, 54 and 50 wt%, respectively, in m-cresol, NMP and concentrated sulphuric acid. The present experiments show that the threshold concentration depends on the polarity of the solvent, shear rate and polydispersity of the polymer. A narrow molecular weight distribution gives a sharper peak with a lower threshold concentration. PBTBH exhibited the typical shear thinning region under low shear rate peculiar to l.c. polymer solutions. The Newtonian plateau and the second shear thinning region under higher shear rate were also observed. Region I behaviour was confirmed by a number of observations, namely (a) the lack of scaling of transient viscosities during startup with strain and (b) the strong dependence of D0 on concentration. In Region I, the viscosity showed a mild dependence on shear rate. This corresponds to a decrease of texture size with shear rate approximately as D−1/2, as in the Wissbrun model. The formation of the l.c. phase was confirmed by polarized light microscopy. Appearance of anisotropic inclusions in an isotropic phase started appearing prior to the occurrence of the critical concentration. As the concentration of anisotropic phase increased, the well known ‘phase inversion’ took place and isotropic inclusions in anisotropic phase started appearing as the system approached the threshold concentration. A fully anisotropic phase above the threshold concentration gave the typical nematic threaded texture under the polarized light microscope. A polydomain microstructure was observed in the shear thinning region under low shear rate, which tumbled down to a monodomain structure on application of higher stress.

Cure characteristics and physicomechanical properties of natural rubber modified with phosphorylated cashew nut shell liquid prepolymer—A comparison with aromatic oil

Natural rubber (NR) has been modified with 10 phr each of phosphorylated cashew nut shell liquid (PCNSL) prepolymer and an aromatic oil (spindle oil) in a typical semi-efficient vulcanization (SEV) system. Despite the lower chemical crosslink density, the PCNSL modified NR vulcanizate showed higher tensile strength, elongation at break, thermal stability, and resistances to fatigue failure and thermo-oxidative decomposition, as compared to the vulcanizate containing the same dosage of spindle oil.

A comparative evaluation of a novel flame retardant, 3-(tetrabromopentadecyl)-2,4,6-tribromophenol (TBPTP) with decabromodiphenyloxide (DBDPO) for applications in LDPE- and EVA-based cable materials

Flame retardation of polymeric materials for cables is becoming a statutory requirement due to governmental regulations to protect life and property from damages caused by fire. This and other factors such as the ever-increasing cost of existing flame retardants (FRs) have given rise to the search for better FRs. In this article, the suitability of an FR, 3-(pentadecyltetrabromo)-2,4,6-tribromophenol (TBPTP) developed from cardanol was evaluated for use in cable insulating and jacketing materials based on low-density polyethylene (LDPE) and ethylene vinyl acetate (EVA). The processability, mechanical properties, compatibility and miscibility, thermal behavior, flammability behavior, smoke generation, acid emission, aging characteristics etc., of the blends of the FR with LDPE and EVA were studied in comparison to those of decabromodiphenyl oxide (DBDPO), which is a standard FR used by the cable industry. Although TBPTP is found to be less thermally stable than is DBDPO, it exhibited better flame retardancy and has comparable thermal stability when blended with LDPE and EVA. Both LDPE-TBPTP and EVA-TBPTP blends produced less smoke than did the corresponding blends of DBDPO. In the case of the EVA-TBPTP blend, the percentage emission of smoke was almost negligible, placing EVA-TBPTP under the low smoke grade. Formulations containing a synergistic agent, promoter, and filler with the corresponding FR and polymer polymer along with an antioxidant were extruded out into wire and tested for cable properties. At 20% loading, the LOI values of the blends were 34.6 and 32.5, respectively, for the TBPTP-EVA and DBDPO-EVA blends. Vertical burning tests carried out with EVA-TBPTP cable showed that it is self-extinguishable. The processability of the compositions containing TBPTP were better than those of DBDPO. The improved processability was found to be due to the plasticising effect of TBPTP. SEM pictures of the blend showed excellent distribution of TBPTP in the polymer, indicating good compatibility and miscibility. Comparatively, DBDPO did not exhibit uniform distribution. The mechanical properties of the blends were within specifications of standard cable materials except that the % elongation of the DBDPO-LDPE blend was far too low. Aging studies also gave better properties for the TBPTP system than for those of the DBDPO system. The overall results show that the properties of EVA-TBPTP cable fall within specifications for the FARLS grade, whereas the EVA-DBDPO cable did not. In the case of LDPE, both TBPTP and DBDPO did not satisfy specifications for the FRLS grade, but the data indicate that they can be used as FRs. The superiority in properties of the TBPTP system over DBDPO is explained in terms of the structure of TBPTP characterized by the distribution of the flame-retardant element, bromine, almost evenly between the aliphatic and aromatic moieties of the molecule, which can, in contrast to the fully aromatic DBDPO, provide halogen over a wide range of temperatures to the combustion zone of the decomposing polymer. Moreover, the presence of the aliphatic segment assures improved processability and compatibility.