Browse Articles

The ways leading to the increase of the flowrate of an extruder of a given geometry are examined, while considering the real situation: screw is rotating and the barrel is stationary; the granules slide onto the surface of the screw; in the granules’ relatively thick layers, relative motion takes place, equivalent to a velocity gradient. Reference was made to the granular material in the feeding zone, to the parameters specific to the feeding zone and their influence on the flowrate, through the values of the friction coefficients onto the barrel and screw (flowrate is proportional with the term , hence an increase in this term in a given case will lead to an increase in the flowrate value). The influence of both the grooves in the feeding zone and of the angle between the direction of movement of the granules and the position of grooves onto the interior surface of the barrel was analysed. There was also considered the posibility of increasing the flowrate through the increase in the bulk density of the granules in the feeding zone, while considering the influence of pressure as well as the ratio between the depth of the screw channel in the feeding zone (adjustable using grooves) and the granules’ diameter. Keywords: extruder floerate, friction coefficient, bulk density, pressure

This paper investigates the rheological properties of some o-sec-butyl-phenoxyacetic esters as a function of temperature, shear rate, and type of the polyol used to prepare the ester. The curves viscosity-temperature and viscosity-shear rate in loop tests at 20, 40, 60, 80oC were obtained and interpreted, and the activation energies of viscous flow and the creep curves were determined. Also, physical and phase changes were analyzed using differential scanning calorimetry (DSC) and correlations between the rheological and thermal behavior were established. Keywords: ester, rheology, DSC

The effect of an organophosphoric insecticide on the thermooxidative degradation of the diglycidil ether-bisphenol A epoxy resin was investigated, using infrared spectroscopy, thermogravimetric and thermodifferential analysis, pyrolysis-gas chromatography and elemental analysis. The results indicated that studied organophosphoric insecticide exercises an influence upon the degradative process of uncured resin by catalysing its decomposition in the lower temperature region. At the same time, the tested insecticide promotes the formation of a phosphorus containing thermostable solid residue. Keyword: epoxy resin, organophosphoric additive, thermooxidative degradation

An experimental study of local heat transfer at the melting of single spherical particles into a flowing liquid is presented in this paper. Local heat transfer coefficient at the particle surface, and local Nusselt number were determined using the photographical technique. Ice-spherical particles having 0,045 m in diameter, and distillated water were used in experiments. The investigations were carried out at the temperature of 303 K at 1 atm pressure, and at several values of water flow velocity ranging from 0,0971 to 0,2279 m/s. The results outline the influence of Reynolds number and proces duration on local Nusselt number. Keywords: heat transfer, local heat transfer coefficient, liquid – solid heat transfer

A series of polydimethylsiloxane-polyethyleneoxide graft copolymers, obtained by hydrosilylation reactions of unsaturated polyethyleneoxides with polysiloxane copolymers containing Si-H groups have been analyzed and characterized from their tensioactive properties point of view and by determination of HLB values. The ratio between the values of siloxane and alkyleneoxide component influences the values of superficial tension (20-37 mN/mm) and of HLB (3-18). HLB values indicate different type of applications of the polymers in various fields. Keywords: silicone surfactants, HLB (Hydrophilic Lipophilic Balance), hydrosilylation, graft copolymers

This paper presents two different procedures for the configuration optimization of a glass fibre reinforced laminate in order to enlarge the load capacity of different structures where these materials could be embedded. By some experimental tests, the authors have established the optimal forming pressure of laminate belonging to a glass fibre fabric reinforced composite. A second experimental aspect taken into account was the determination of the optimal number of laminate, in both situations being attended the obtainment of the highest values for ultimate strengths. The Finite Element Method gives the possibility of a constructive optimization of the composite, the parameters taken into consideration depending on the followed purpose. Keywords: epoxy resin, lamina, finite element method, forming pressure, interlaminar strength

The paper investigates the effect of organic phase on yield and inherent viscosity in liquid-vapor interfacial polycondensation and the effect of reaction temperature and reagents molar-ratio on yield, inherent viscosity and molecular weight in liquid-liquid interfacial polycondensation of cyclohexylphosphonic dichloride (CPD) with bisphenol A (BA). A comparative study between liquid-liquid and vapor-liquid interfacial polycondensation of CPD with BA was performed. Keywords: polyphosphonate, interfacial polycondensation, bisphenol A, cyclohexylphosphonic dichloride

Waxes are critical to hot melt adhesives performance in terms of thermal stability and mechanical properties. The thermal behavior of EVA with microcrystalline and polyethylene waxes have been investigated by infrared spectroscopy and physical-mechanical testing. Infrared spectroscopy was used to follow the ratio evolution of band intensities E730/E720 with type and content of EVA –wax blends. The tensile properties have been measured at two EVA/wax ratios: initially and after exposure at 175 and 200oC. A significant correlation was found among tensile strength at break / elongation and type and ratio of EVA / wax ratio. Semiquantitative spectral information and evolution of physical – mechanical properties have been used to improve the behavior of EVA hot melt adhesives at work temperature. Keywords: wax, elastomers EVA, thermodegradation, cristallinity

Powders of poly (vinyl alcohol) with different degrees of polymerisation and hydrolysis have been reacted with phosphorous acid in homogeneous conditions. The influence of experimental conditions on the substitution degree has been investigated. Analytical, spectral, viscosimetric and thermogravimetric methods were used to analyse the influence of tacticity, crystallinity and degree of polymerisation and hydrolysis of parent poly (vinyl alcohol) on the properties of the phosphorilated products. Keywords: phosphorilated poly (vinyl alcohol), degree of hydrolysis, degree of polymerisation, tacticity

Epoxy resins with mezogenic groups were prepared from diglycidyl ether of 4,4`-bisphenol (DGEBP), as rigid block, and 4,4’-diaminodiphenyl sulphone (DDS), as curing agent. A nematic-like structure was developed in time, in the temperature range of the curing process between 151 and 2530C. The mesophase formation was proved using optical microscopy (OM) and wide-angle-X-ray scattering (WAXS) techniques. Keywords: epoxy, mesophase, liquid crystal, curing, network