A. R. R. Menon

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.

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.

Influence of Body Position on Severity of Obstructive Sleep Apnea: A Systematic Review

Aim. The aim of this review is to determine the relationship between sleeping body posture and severity of obstructive sleep apnea. This relationship has been investigated in the past. However, the conclusions derived from some of these studies are conflicting with each other. This paper intends to summarize the reported relationships between sleep posture and various sleep indices in patients diagnosed with sleep apnea. Methods and Materials. A systematic review of the published English literature during a 25-year period from 1983 to 2008 was performed. Results. Published data concerning the sleep apnea severity and posture in adults are limited. Supine sleep posture is consistently associated with more severe obstructive sleep apnea indices in adults. However, relationship between sleep apnea severity indices and prone posture is inconsistent.

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.

Stress-relaxation characteristics of natural rubber modified with phosphorylated cashew nut shell liquid prepolymer

The tensile stress-relaxation characteristics at room temperature of gum NR vulcanizates containing 10-20 phr of phosphorylated cashew nut shell liquid (PCNSL) prepolymer were studied at various strain rates and strain levels, in comparison with that containing the same dosage of 2-ethyl hexyl diphenyl phosphate and the unmodified sample. Modification of NR with 10-15 phr of PCNSL resulted in improvements in tensile properties along with a lower degree of stress relaxation at the higher strain rates and strain levels.

Studies on blends of melt-processable liquid crystalline polymers and thermoplastics. I. Blend of polyesteramide with polyethylene

The processability characteristics, physicomechanical properties, and thermal decomposition characteristics of blends of low-density polyethylene (LDPE) and polyesteramide (PEA), a thermotropic liquid crystalline polymer, were studied using various analytical techniques. Studies on a Brabender Plasticorder at temperatures ranging from 170 to 230°C showed good melt processability for the blends. The melt rheology of the blends containing 0–15% of PEA at 170°C was studied using a capillary rheometer (Goettfert) fitted with a circular die (L/D = 30/1) at apparent shear rates ranging from 12 to 2300 s−1. The samples containing PEA showed a comparatively lower die swell at high shear rates. X-ray diffraction measurements showed a reduction in crystallinity of LDPE in the presence of 2–4% of PEA. Scanning electron microscopic evaluation of the morphology of the fractured surface of the blend showed some degree of orientation, but not to the level typical of LCPs. However, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicated significant improvement in the resistance to thermooxidative decomposition of LDPE modified with PEA.