Jaroslava Budinski-Simendić

Study of the Effect of Soft-Segment Length and Concentration on Properties of Polyetherurethanes. I. The Effect on Physical and Morphological Properties

Abstract 1. Densities of elastomers with crystallizing soft segments were higher than that of the noncrystallizing ones. However, the effect of the soft segment length is not regular and may reflect some specific interactions between two phases as well as instantaneous morphology. 2. Phase inversion as judged by drop of hardness takes place at about ssc=60° or more; a shift to higher ssc gives a greater segment length. 3. Tg of the soft segment in samples with well separated phases is independent of ssc, e.g., the presence of hard phase does not change mobility of the soft phase in samples with ssc=50° or more, in all series. However, Tg is strongly dependent on the soft-segment length. Tg for the soft segment of Mn=650 was −43°C, for Mn=1000 was −62°C, and for Mn=2000, Tg was −75°C. The effect of the presence of the hard phase on mobility of the soft phase seems to vanish for M>2500. 4. Tg of the hard segment at 77°C was clearly observed only in quenched samples with a high hard-segment concentration (80...

Effect of addition of polyethylene on properties of polypropylene/ethylene–propylene rubber blends

Toughening of polypropylene was carried out by adding two types of ethylene-propylene rubber (EPR) having different ethylene content, and three commercial types of EPR containing high density polyethylene (PE). The concentration of EPR was varied from 0–30%. Globular morphology of the dispersed phase was observed at all concentrations. Average particle size of the dispersed phase (EPR) was about 2–4 μm with about 10% within the 0.5–1 μm range. Although most of the properties were not affected by the presence of polyethylene, high notched Izod impact strength was achieved only with samples containing PE. Melt flow rate, yield strength and modulus were found to decrease almost linearly with increasing elastomer concentration in the blend. Elongation at break was enhanced by the addition of EPR, particularly those containing PE. The contribution of PE to the properties was explained by the specific EPR/PE particle morphology (core-shell or interpenetrating) but the exact mechanism of toughening of PP with EPR in the presence of PE is not clear.

Synthesis and Characterisation of Polyester Based on Isosorbide and Butanedioic Acid

Copolyesters based on isosorbide and butanedioic acid in combination with monomers such as adipic acid and dimethyl terephthalate, poly(isosorbide-co-butanedioic acid) (and -co-adipic acid) and poly(isosorbide-co-butanedioic acid-co-dimethyl terephthalate), were synthesized and characterized. Linear OH-functionalized polyesters were obtained via melt polyesterification of dicarboxylic acids with OH-functional monomers. The type of end-group was controlled by the monomer stoichiometry and hydroxyl functional group is formed in time. Average molecular masses of synthesised polyesters were measured by gel permeation chromatography. The glass transition temperatures and thermal stability of the obtained polyesters were effectively adjusted by varying polymer composition and molar mass. Addition of adipic acid or dimethyl terephthalate increased glass transition temperatures of obtained polyesters. Thermal stability of obtained polyester slightly increases by the increasing of dimethyl terephthalate content. Molecular structures of obtained polyester were assessed by Fourier transform infrared spectra and 1H NMR spectroscopy.

The effect of gamma radiation on the ageing of sulfur cured NR/CSM and NBR/CSM rubber blends reinforced by carbon black

In this work the effect of the γ-radiation dose on ageing of carbon black reinforced elastomeric materials was studied. The compounds based on natural rubber/chlorosulfonated rubber blend (NR/CSM) and butadiene acrylonitrile rubber/chlorosulfonated rubber blend (NBR/CSM) (50:50, w/w) with different loadings (0, 20, 40, 50, 60, 80 and 100 phr) of the filler with the average particle size of 40 nm were cured by sulfur. The obtained elastomeric composites were subjected to radiation doses (100, 200, 300 and 400 kGy) in the presence of oxygen. The changes of material mechanical properties were estimated after radiation accelerated ageing. By using Fourier transform infrared measurements (ATR-FTIR) it was assessed that after exposure to doses of 100 kGy alcohols, ethers, lactones, anhydrides, esters and carboxylic acids are formed in materials. The formation of shorter polyene sequences and aromatic rings in aged samples are assumed on the basis of the obtained spectra.

Study of the Effect of Soft-Segment Length and Concentration on Properties of Polyetherurethanes. II. The Effect on Mechanical Properties

Abstract Three series of segmented polyurethanes with different soft segment lengths and concentrations were examined by TMA, DMA, and mechanical methods. Maximum tensile strengths were obtained when ssc was 40–50%, which was explained by a specific interlocking morphology. No significant effect of soft-segment chain length on maximum strength was found, but higher values were found in the C series when ssc was 60%. Elongation at break increases linearly with ssc but indications that shorter soft segments produce higher extensions was attributed to plastic flow. TMA showed that Tg was independent of ssc in the C and, to a degree, in the B series, while temperature of α-transition in DMA was independent of ssc only in the C series at ssc above 50%.

Structural Differences Between Lignin Model Polymers Synthesized from Various Monomers

In a plant cell wall, lignin is synthesized from several monomeric precursors, combined in various ratios. The variation in monomer type and quantity enables multifunctional role of lignin in plants. Thus, it is important to know how different combinations of lignin monomers impact variability of bond types and local structural changes in the polymer. Lignin model polymers are a good model system for studies of relation between variations of the starting monomers and structural variations within the polymer. We synthesized lignin model polymers from three monomers, CF—based on coniferyl alcohol and ferulic acid in monomer proportions 5:1 and 10:1 (w/w), CP—based on coniferyl alcohol and p-coumaric acid in proportion 10:1 (w/w) and CA—based on pure coniferyl alcohol. We studied structural modifications in the obtained polymers, by combining fluorescence microscopy and spectroscopy, FT-IR and Raman spectroscopy, in parallel with determination of polymers’ molecular mass distribution. The differences in the low Mw region of the distribution curves of the 10:1 polymers in comparison with the CA polymer may be connected with the increased content of C=C bonds and decreased content of condensed structures, as observed in FT-IR spectra and indicated by the analysis of fluorescence spectra. The 5:1 CF polymer contains a different type of structure in comparison with the 10:1 CF polymers, reflected in its simpler Mw distribution, higher homogeneity of the fluorescence emitting structures and in the appearance of a new high-wavelength emission component. We propose that this component may originate from π-conjugated chains, which are longer in this polymer. The results are a contribution to the understanding of the involvement of structural variations of lignin polymers in the cell wall structural plasticity.

Synthesis and properties of novel star-shaped polyesters based on l -lactide and castor oil

The topology of biodegradable polyesters can be adjusted by incorporating multifunctional polyols into the polyester backbone to obtain branched polymers. The aim of this study was to prepare the biodegradable-branched polyester polyols based on l-lactide and castor oil using the trifluoromethanesulfonic acid as a catalyst. FTIR and 1H NMR spectroscopy measurements were used to estimate the molecular structure of the novel materials. The polyester polyol was synthesized by ‘‘core-first” method which involves a polymerization of l-lactide by using a castor oil as multifunctional initiator. Molar masses estimated by gel permeation chromatography and vapor pressure osmometry were in good correlation with calculated values based on hydroxyl number of obtained polymers. DSC measurements confirmed high crystallinity degree of the synthesized material. It was assessed that the molar masses of obtained polymers-influenced glass transition temperature significantly. The thermal stability was investigated by TG analysis, and the results have shown the dependence of weight loss on the arm length of the star-shaped polyesters. The thermal stability of star-shaped polyesters significantly decreased with degradation of polyester polyol obtained in acid solution.

The Effect of Accelerators on Curing Characteristics and Properties of Natural Rubber/Chlorosulphonated Polyethylene Rubber Blend

The aim of this work was to determine the influence of accelerator type on curing behavior and properties of sulphur vulcanized rubber blend based on natural rubber (NR) and chlorosulphonated polyethylene (CSM). In NR/CSM compounds filled with carbon black three types of accelerator were used: N-cyclohexylbenzothiazylsulphenamide (CBS), tetramethylthiuram disulphide (TMTD), and 2-mercaptobenzothiazol (MBT). The curing characteristics were estimated using oscillating disk rheometer. The results revealed that the accelerator type not only affects the cure characteristics, but also has great influence on the mechanical properties of obtained elastomers. It was determined that the tensile strength of rubber blends cured in the presence of TMTD was relatively high.

Preparation and Thermal Stability of Elastomers Based on Irregular Poly(urethane-isocyanurate) Networks

The objective of this study was to investigate the thermal stability of poly(urethane-isocyanurate) networks with increasing amount of dangling chains. In order to improve thermal stability of elastomeric materials, networks were prepared by adding some heat resistant isocyanurate rings as a junction points by catalytic cyclotrimerisation of telechelic diisocyanates. The thermal degradation kinetics of samples has been studied by means of high-resolution thermal analyzer SDT Q600 TA Instruments, under nitrogen atmosphere. The activation energy for the two step reactions of thermal decomposition of different species was calculated and compared.

Effect of the ratio of reactive groups on gelation and cyclization during polyurethane network formation

Abstract The effect of the initial molar ratio of the reactive groups, r NCO (= [ NCO ] 0 [ OH ] 0 =1.0 or 0.8) , on the gelation of polyurethane networks based on tris(4-isocyanatophenyl)thiophosphate and poly(oxypropylene) diol, was studied. The number-average molecular weight, M n , in the pre-gel state, the critical conversion at the gel point, pcNCO, and the critical ratio, rcNCO, at which gelation occurs, were measured. The decrease in 1 r c NCO with increasing dilution in xylene suggests that cyclization takes place. The experimental M n values are always lower than the theoretical ones, with the latter being calculated for the ring-free case. The fraction of bonds that are lost in the cyclization process, s, calculated from the difference between the experimental and theoretical values of M n , increases with conversion and has a value near the gel point of 0.04–0.06. It is demonstrated both theoretically and experimentally that the values of s calculated from the shift of the gel point conversion are not equivalent to those obtained from M n , but depend on rNCO.