D. Joseph Francis

Rheological characterization of blends of low density with linear low density polyethylene using a torque rheometer

Abstract Selected grades of LDPE and LLDPE have been melt-mixed over the complete range of compositions. The shear flow behaviour in the melt and the stress-strain behaviour in the solid phase of the blends show smooth variations with composition and are intermediate between those of the parent polymers. While LLDPE improves the mechanical strength of the blends, LDPE makes easier the processing of the blends, requiring low energy input.

Effect of controlled crosslinking on the mechanical and rheological properties of hdpe/lldpe blends

Abstract High density polyethylene and linear low density polyethylene have been melt-mixed over the complete range of compositions and the mechanical and rheological properties of the blends have been evaluated. A low degree of crosslinking has been introduced in the matrix by adding one percent dicumyl peroxide. The crosslinking is found to improve the mechanical properties without adversely affecting the processing characteristics.

Structure Property Processing Relationships in Chemically Modified LDPE and LDPE/LLDPE Blend

The properties of low-density polyethylene (LDPE) and its blend with linear low-density polyethylene LDPE : LLDPE (75 : 25) modified with varying concentrations of dicumyl peroxide (DCP) were compared. Chemical modification was carried out in a Brabender plasticorder under set conditions of temperature, rotor speed, and time. The results are reported in terms of the type of polyethylene used, concentration of DCP, mixing torque, temperature and time on the processing, and mechanical and physical properties of the modified samples. Interpretation of the results is given in terms of gel contents which relate to the three-dimensional network structure of polyethylene. The modified blend forms a denser network structure and, hence, better product properties relative to that of modified LDPE, indicating the influence of LLDPE in increasing the rate and extent of crosslinking on blending with LDPE.

Effect of fillers in the binary systems containing TMTD–amidinothiourea and MBTS–amidinothiourea in NR vulcanization

In earlier studies,1,2 we have shown that in MBTS–amidinothiourea and TMTD–amidinothiourea binary system of rubber vulcanization, amidinothiourea functions effectively as a secondary accelerator and improves the accelerator activity of these systems. These secondary accelerators enhance the physical properties of the vulcanizates and show better cure characteristics of the mixes compared to the reference systems studied. In this paper, we present the results of our study on the effect of various fillers in the sulfur vulcanization of natural rubber using amidinothiourea as the secondary accelerator. We have taken MBTS–amidinothiourea and TMTD–amidinothiourea binary accelerator systems and vulcanizates were prepared with carbon black, precipitated silica, and china clay as fillers. Different compositions of amidinothiourea were used in various mixes using standard recipes. Reference mixes were also studied. Curing characteristics of the mixes and various physical properties of the vulcanizates were evaluated. Optimum dosage of amidinothiourea required has also been derived. Among the different secondary accelerators tried including amidinothiourea, it may be stated generally that the more nucleophilic the secondary accelerator, the less the optimum cure times. This fact points to a nucleophilic reaction mechanism in the systems under review. In the evaluation of tensile and other physical properties of the vulcanizates, some of the systems containing amidinothiourea show better properties while others give comparable values with the reference mixes. Estimation of crosslink density also supports the above conclusion.

Studies on the Cure Characteristics and Vulcanizate Properties of 50/50 NR/BR Blend

Abstract A carbon black filled 50/50 Natural Rubber (NR)/Polybutadiene Rubber (BR) blend is vulcanized using several conventional systems designed by varying the amounts of sulphur and accelerator. The cure characteristics and the vulcanizate properties are compared. The quality and quantity of crosslinks in each case are deciphered by chemical probes to correlate them with the vulcanizate properties.

Scanning Electron Microscopic Studies of PP/EPDM/NR Ternary Blends

The morphological properties of PP/EPDM/NR blends were investigated. A double layered morphological structure was observed for the compression moulded PP/EPDM/NR blends. Blends with low levels of elastomer content show a particulate distribution in the elastomer phase. For the 80/10/10 blend an interpenetrating co-continuous network is observed. The same blend shows the highest impact strength.

Treatment of natural rubber latex concentration wastewaters by stabilisation pond

The feasibility of treating wastewater from a natural rubber latex concentration unit alone and in admixture with domestic sewage in a waste stabilisation pond was studied. The results clearly indicate that the waste stabilisation pond method is quite effective in treating the natural rubber latex concentration waste water in admixture with sewage. The percentage BOD and COD reduction ranged from 69 to 93 and 65 to 90, respectively. The algal counts in wastewater‐sewage mixture varied from 30 × 104 to 167 × 104/ml. While many species of algae grew well in the wastewater‐sewage mixture, Microcystis aeruginosa, Chlorella vulgaris, Euglena acus and Scenedesmus quadricauda predominated.

Radiation Crosslinking of HDPE/LLDPE Blends in the Presence of Dicumyl Peroxide

Blends of HDPE and LLDPE have been modified by gamma radia tion in the presence of dicumyl peroxide. The modification is found to introduce a low level of crosslinking in the matrix without seriously affecting the crystal linity. Properties, such as yield stress, tensile strength, and abrasion resistance improve with the irradiation.

Scanning Electron Microscopy Examination of the Fracture Surface of NR/SBR and NR/BR Blends

Abstract Blending of two or more rubbers is carried out for three main reasons,1 (1) improvement in technical properties (2) better processing (3) lower compound cost. Many products in the rubber industry are based on blends in all or part of their construction. Tyres are typical examples of products in large-scale volume production. Natural rubber (NR)/styrene-butadiene rubber (SBR) and natural rubber/polybutadiene rubber (BR) blends are extensively used in the manufacture of tyres.2 Scanning electron microscopy (SEM) is now widely employed to observe the microstructure of fracture surfaces and hence to study the fracture mechanism3-5. Fracture may be caused due to faults in the material or operating conditions. The fracture surfaces of polymeric materials show many characteristic features which enable the destructive influence to be recognized. Since the mechanical behaviour of blended rubbers is very sensitive to the filler distribution and level,6-8 curing aspects,9-11 compatibility of the rubber12-14...

Modification of Polychloroprene with Polyvinylchloride

Abstract Polychloroprene (neoprene) has been blended with polyvinylchloride (PVC) in different proportions using a new stabiliser system (magnesium oxide and zinc oxide with stearic acid) for PVC. The physical properties of the blends show that they can advantageously replace neoprene in many applications.