The paper presents the methodology of determining the plasticity of some composites specimen through bending test. The equipment is presented both for room temperature testing and under cryogenic conditions. Particularities of the measurements under cryogenic conditions are specified. The influence of talc concentration in the composite material is presented. Key words: composite materials, deflection, cryogenics.
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The study presents rheological behaviour of some solution mixtures from poly(vinyl alcohol) (PVA) and starch in water, with addition of glycerol as plasticizer and urea (nitrogen source for microorganisms). These solutions were used to obtained biodegradable films. The effect of temperature and concentration on the rheological behaviour of poly(vinyl alcohol) and starch solutions in water, was studied in the temperature range of 20-60 0C and concentration 10-20 % at different gravimetrical ratio PVA/starch (3.00, 1.66, 1.00, 0.60, 0.33). The rheological behaviour was studied to gradient of shear rate which varied between 3 and 1310 s-1. From experimental data it was established that concentrated solutions of PVA/starch blends exhibit a non-newtonian rheological behaviour of pseudoplastic type. The flow activation energies versus temperature are situated in range of 11.86-49.92 kJ/mol, while against the concentration between 1.61-4.54 kJ/mol. The consistency index increased with decrease of temperature and recording great values in the concentrated solutions case. The solutions with PVA/starch subunitar gravimetrical ratio have great values of consistency index, to compare those with supraunitar ratio. This fact shows that the starch is the polymer which confers solutions a great viscosity, but low temperatures determines even their jellification. Keywords: biodegradable materials, rheological behaviour, poly(vinyl alcohol), starch
Cross-linked polyurethane/filler composites based on polyester, diphenylmethane diisocyante, glycols, and glycerin were synthesized and characterized. The mechanical and thermal properties of PU/filler composites were investigated through tensile, thermogravimetry experiments. Therefore, to understand the behaviour of fillers, such as graphite, talc, CaCO3, and polyamide fiber added to cross-linked polyurethane resins, several thermal and mechanical tests were conducted on samples, using these new materials. It is shown that cross-linked polyurethane composites have decreased tensile strength, improved hardness and thermal stability, relative to bulk polyurethane. The results show that the polyurethane component ratios in cross-linked polymers, the types of filler, and the amount of powder added all affect the damping behaviours and degree of phase separation of unfilled and filled cross-linked polyurethanes. The addition of filler into polyurethane composites yields an increase in the Young´s modulus and a decrease in the elongation at break. Keywords: composite, cross-linked polyurethane, mechanical properties, filler
A series of phosphorous-containing copolyesters was prepared by polycondensation of 2-(6-oxido-6H-dibenzo[c,e][1,2]oxaphosphorin-6-yl)1,4-benzenediol, 1, or of an equimolecular amount of 1 and different aliphatic diols 2, such as: ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol and 1,12-dodecanediol with an aromatic diacid chloride containing two preformed ester groups 3, namely terephthaloyl-bis-(4-oxybenzoyl-chloride). The copolyesters exhibited good thermal stability having the decomposition temperature above 360°C and char yield at 700°C in the range of 8.4-41%. The glass transition temperature was in the range of 83-160°C. The polymers exhibited thermotropic liquid crystalline behaviour. Keywords: polyesters, phosphorus-containing polymers, solution polycondensation, thermal properties
Some methods for the preparation of cellulose microfibrils and polymer composites with such microfibrils are presented in this paper. Morphological aspects of microfibrils and their dispersion in the polymer matrix are characterized using SEM and optical microscopy. Cellulose microfibrils show a clear reinforcing effect of the polymer matrix as pointed out by mechanical characterization. Keywords: polymer composites, cellulose microfibrils, mechanical properties
The paper presents the kinetic characteristics in non-isothermal conditions obtained by degradation in argon of some aromatics copolyethers with semi rigid and flexible spacer and by comparing the results obtained for the homopolyethers corresponding to the bisphenols and spacer used. Copolyethers were synthesised by phase transfer catalysis method in liquid/liquid system. Oxetanic, diethyl etheric or hexamethilenic spacers have been used. 4,4’-dihidroxy azobenzene and 4,4’ dihidroxy biphenyl were used as bisphenol. Thermogravimetric analysis and derivative thermogravimetric analysis were applied. The kinetic characteristics suggest the complexity of the thermal degradation mechanism up to 1000°C. The degradation rate is depending on the chemical structure of the main chain. Compensation equations are proposed. Keywords: kinetic characteristics, aromatic copolyethers, thermal degradation
The topochemistry of the process of suspension alkoholysis of vinyl polyacetate has been studied. It was thus demonstrated that the alkoholysis occurs in three stages: the first takes place in the homogeneous phase, the second in the gel phase, and in the third sineresis takes place a process that leads to forming a numerous pores within the polyvinyl alkohol pearls fact demonstrated by SEM. This study made possible to propose a mechanism, through which the pores are formed as well as the dependence of pearl porosity on the concentration of initial vinyl polyacetate solutions subjected to alkoholysis. Keywords: alkoholysis, polyvinylacetate, polyvinylalcohol
In this paper, a comparative study was conducted on the behaviour of three types of thermoplastic materials during the injection molding of a complex part using the Moldflow software. The numerical simulation is based on the Hele-Shaw flow model for the inelastic non-Newtonian fluids under non-isothermal conditions. Based on the numerical results accurate prediction of weld lines and air traps were carried out. Keywords: injection molding, plastic materials, air trap, weld line
The radial, branched, styrene-butadiene block-copolymers with different polybutadiene block microstructures have been synthesized via anionic two stages sequential polymerization of monomers in solution, followed by the coupling reaction with SiCl4. This synthesis route involves the polymerization of styrene first, and after that polystyril-lithium was modified with variable amounts of tetrahydrofurane before introducing the butadiene, in order to obtain the middle polybutadiene block with different microstructure. The paper shows the effect of the polybutadiene block microstructure on the HDPE blending modification. The HDPE modification is meant to improve the mechanical properties, especially impact resistance.
Synthesis of pyridine groups grafted on copolymers is described. The method is applied, extended and optimised for gel-type styrene-divinylbenzene copolymers (S-DVB) with 5% and 7% degree of crosslinking. Keywords: 2-amino-pyridine pendant groups, styrene-divinylbenzene copolymers