Browse Articles

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

Implementation of composite materials, especially of glass fibers reinforced ones, lead to replacement of classic materials, whose supplies are more and more limited. The machinability, as well as the machining procedures, of polymeric composites depend on various factors, such as matrix and reinforcing element types; the orientation of reinforcing elements, manufacturing method, etc. Thermal phenomena, occurring while machining, are very important, because the temperature into the cutting zone must not exceed certain value corresponding to vitrifying temperature. So, this paper presents the most important aspects required in order to obtain a mathematical model of temperature, as function of machining parameters, in cylindrical – face milling of glass fibers reinforced polymeric composites. Keywords: polymeric composite, glass fibres, milling, regression function

This paper presents the influence of the processing temperatures on the physico – mechanical properties of PC used in injection molding of high performance sport products. The samples (test-pieces) were obtained by processing PC at the following temperatures: 280°C, 295°C, 310°C, 325°C and 340°C. It was established that the pressure in the mold decreases as the processing temperature rises. Further, thermal analyses were performed (TG, DSC, and DMA) and it was noticed that the processing temperature had an influence on the thermal stability of the polymer and on the activation energy (Ea) of the glass transition phase, but the glass transition temperatures Tg were slightly influenced by the processing temperature. Keywords: polycarbonate, injection molding, TG, DSC, DMA

The paper shows a series of data concerning the formation and lignin nature of polymeric deposits built up at the beechwood pre-hydrolysis. By means of elemental compostion, data limit formulas (empiric) of deposits have been calculated also emphasizing the special influence of hidromodule over the structure of deposits. The second part of the paper shows aspects related to the recovery of lignin polymeric deposits in order to synthetize a lignin-phenol-formladehyde resin, useful to the wood processing sector as well as the energy sector. Keywords: pre-hydrolysis, beech, limit formulas (empiric), lignin-phenol-formaldehyde resins