Browse Articles

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

Functional polyamides with hydroxyl pendant groups were prepared by the direct polycondensation of 5,5`-methylene-bissalicylic acid, with various diamines (p-phenylenediamine, 4,4’-oxydianiline and 4,4’-methylenedianiline) in N-methyl-2-pyrrolidone, using triphenyl phosphite and pyridine as condensing agents. The resulting polymers were chemically modified with 4-maleimidobenzoyl chloride, resulting in polyamides with maleimide pendant groups. The polymer structures were confirmed by elemental analysis data and spectroscopic (IR, 1H-NMR) characterizations. Their inherent viscosities were in the range of 0.22 to 0.34 dlg-1. The polymers were soluble in dipolar aprotic solvents such as dimethylsulfoxide, dimethylformamide, and were thermally stable up to 314 °C. The chemically modified polyamides exhibited better solubility and thermal stability than their unmodified counterparts. Keywords: polyamide, maleimide, Yamazaki-Higashi polycondensation, reactive polymers

The aim of the present work is to investigate the effect of different stress levels on the creep and recovery behaviour of polymer-matrix composites. Four hours creep followed by two hours recovery tests were performed to woven GFRP specimens at five different stress levels corresponding to five different percentages of ultimate static strength. Since the behaviour was linear viscoelastic, a four element viscoelastic model was applied. In addition, the viscoelastic behaviour observed was correlated with the degree of damage generated due to creep and its variation with the applied stress levels. Keywords: creep, recovery, linear viscoelastic behaviour, four parameter model

Both the theoretic elements of an interferometric method for the refractive index determination based on a Fabry-Perot etalon and the procedure of the Fabry-Perot cell obtaining are described in this paper. The results obtained by this method for PVA isotropic foils and for PVA foils including small amounts of potassium iodide are given here. Keywords: PVA, FPE, refractive index, isotropic materials