Drago Hace

Role of the polyurethane component in the adhesive composition on the hydrolytic stability of the adhesive

Abstract In polyurethanes based on linear polyol, isocyanate and a chain extender, the physical morphology of adhesive seems to play an important role in its overall strength characteristics. The aim of this paper is to examine how the morphology and phase separation of such polyurethane components affect the adhesive properties before and after hydrolysis. It is shown that effective microphase separation and the development of hydrogen-bonded structures, as well as hydrolytic events in the hard segment domains, depend strongly on the adhesive composition. The influence of the environment on polyurethane adhesives can be countered by proper selection of the polyurethane component.

Tensile properties of calcium carbonate-reinforced poly(vinyl acetate)

In certain applications, a reinforced composite is used as an adhesive layer. In this study, the bulk mechanical behaviour of composite films based on a poly(vinyl acetate) (PVAc) matrix and various calcium carbonate (CaCO3) fillers was investigated. The interactions depend on the morphology and chemical structure of the filler and the polymer matrix. The polar natures of both PVAc and CaCO3 have a strong influence because of acid-base interactions. The tensile properties of PVAc/CaCO3 composites showed an increase in strength at break with increased filler concentration. The interactions can be modified by surface pretreatment of CaCO3 with stearic acid, which lowers the surface interaction and changes the degree of filler dispersion in the PVAc matrix. Micrographs confirmed the tendency of small CaCO3 particles to agglomerate and as a consequence, discontinuity of the composite film is observed. An effective surface treatment reduced the particle agglomeration tendency, which improved the film elongatio...

Mechanical properties of adhesive thin films

In this paper, a poly(vinyl acetate) (PVAc) adhesive in the form of a film was considered to be a composite. Its mechanical properties changed with filler addition owing to the interactions at the polymer/filler interface. The experimental results were fitted with various theoretical and empirical equations that describe the dependence of mechanical properties on filler volume fraction. In this way, the coefficients calculated from the mostly empirically broadened equations for the case of adhesion between the matrix and filler gave the opportunity to determine the interactions between the PVAc matrix and various fillers quantitatively.

Investigation of the Influence of Fillers on the Properties of Poly(vinyl acetate) Adhesives

The properties of poly(vinyl acetate) compositions prepared as potential wood adhesives were investigated. The paper presents the results of the influence of various kinds of inorganic fillers based on calcium carbonate and alumino-silicate and an organic filler, starch, on the adhesive composition properties. The comparison among rheological behavior of the adhesive dispersions concerning the specific role of fillers were made. Mechanical and relaxation properties of the adhesive films could reveal the effect of filler characteristics on the polymer matrix. The significant influences of particle size distribution and specific surface area on the poly(vinyl acetate) adhesive composition were determined, along with other filler characteristics.

Copolymerization of α-methylstyrene with N-alkylmaleimides

SummaryAlternating copolymers of α-methylstyrene (α-MeSt) with N-alkylmaleimides (RMI; R=Et, n-Pr, iso-Pr, n-Bu, n-Hex) were prepared in Calvet differential microcalorimeter under different monomer-to-monomer ratios in the feed using AIBN as initiator. The equilibrium constants of CT-complex monomers have low values: 0.02–0.05 L.mol-1 but the mechanism of copolymerization indicates the participation of CT-complex. Equilibrium constants and rate of decomposition under the TGA conditions are not dependent on steric factors, but the rate of copolymerization decreases with the increase of bulkiness of alkyl substituent. In high conversion copolymerization it was observed that in the presence of an excess of homopolymerizable RMI, alternating copolymers are quantitatively formed prior to the formation of poly(RMI).

Copolymerization ofα-methylstyrene with 4′-N-(benzo-15-crown-5)maleimide

Summary4′-N-(Benzo-15-crown-5)maleimide (I) was prepared by dehydration of the corresponding maleamic acid (IV). The complexation constant, K=0.07 L mol−1, between I and ∝-methylstyrene (∝-MeSt) was determined by modified Benesi-Hildebrand NME method. The copolymerization of ∝-MeSt with homopolymerizable I at different monomer-to-monomer ratios in the feed was performed up to high conversion in Calvet microcalorimeter. It was found that in the copolymerization of ∝-MeSt with an excess of I, the alternating copolymerization precedes the homopolymerization. The mixture of alternating copolymer and homopolymer of I has a single Tg, thus indicating the miscibility on molecular level.

The extraction of sodium and potassium picrates with poly[(benzo-16-crown-5)maleimide], poly[(benzo-15-crown-5) maleimide-alt-α-methylstyrene] and benzo-15-crown-5

The distribution of complexes of sodium picrate and potassium picrate with poly[(benzo-15-crown-5)maleimide], poly[(benzo-15-crown-5)maleimide-alt-α-methylstyrene] and benzo-15-crown-5 (b15/5) between water and CH2Cl2 was investigated. Concentration of Na-ion with homopolymer in CH2Cl2 was 52%, while the concentration of complex of alternating copolymer and b15/5 with Na-ion was 22% and 20% respectively. Concentration of K-ion complex in CH2Cl2 with homopolymer and alternating copolymer was 90% and with b15/5 the concentration of complex was 40%. The large difference in the complexation ability of Na-ion and K-ion with homopolymer and alternating copolymer is considered to be the consequence of the formation of 1:1 complex with Na-ion and 2:1 complex with K-ion.

Influence of thermal and UV radiation on polystyrene structure

Abstract The glass transition temperatures have been measured on atactic polystyrene after thermo-oxidative and photo-oxidative degradation. For comparison, DSC patterns of degraded samples were made. The DSC patterns were found to be quite sensitive to small changes in polymer structure and types of linkage. Examination of the data shows that T g values of degraded samples are shifted to lower values, and several T g transitions have occurred as the degradation time is proceeding. The X-ray diffraction pattern obtained from a specimen of polystyrene is characteristic of that of an amorphous material, viz. it consists of broad and diffuse haloes. The study of the scattering from polystyrene, as a function of temperature and UV irradiation, has revealed a change in location, shape and intensity of the scattering pattern. It is shown that these results can be interpreted in terms of definite structural changes which take place during polystyrene degradation.

Effect of styrene/ethylene/butylene/styrene block copolymer on the dynamic mechanical behaviour and processability of high-impact polystyrene

Abstract Blends of high-impact polystyrene (PS-HI) and styrene/ethylene/butylene/ styrene block copolymer (SEBS) were investigated to determine the effects of rubber on the polymer properties. The processing behaviour of the PS-HI + SEBS blends was analyzed and the dynamic mechanical behaviour of the processed blends was examined. The rheological behaviour of the prepared blends during processing was followed by measuring the torque, output and melt pressure in a twin extruder. Dynamical mechanical analysis was performed in the temperature range of -150 to 160°C. The blends were also investigated in the creep fatigue regime and relaxations were determined at 25 - 65°C. Master curves for the reference temperature 25°C were created using the time-temperature superposition principle. With increasing SEBS content there was not significant increase of the torque value for blends below a rubber content of 70 wt.-% with respect to neat PSHI. An influence of SEBS content on the increase of the apparent viscosity was observed above 40 wt.-% of SEBS. The curves of storage modulus E’, loss modulus E’’ and loss tangent tan δ vs. temperature are affected by lowering the hard phase (PS) content: tan δ of the soft phase ethylene/butylene (EB) increases, while tan δ for the hard phase and storage modulus decrease. All samples exhibit a single glass transition of the hard phase. At constant load the creep of PS-HI, SEBS and PS-HI + SEBS blends increases and the creep modulus decreases over a period of time for all samples examined. These effects are more pronounced in samples with lower hard phase content. The energy-time-temperature correspondence principle was applied to create master curves for the reference temperature 25°C for the creep modulus of PS-HI, SEBS and PS-HI + SEBS blends. Microscopic morphology results confirm the main conclusions obtained from the processing and dynamic mechanical behaviour of the blends. The phase-separated microstructure is more pronounced in PS-HI + SEBS blends. The rise in fracture energy with SEBS introduction appears in the whiteness of the SEM microphotographs, first as white crests, and in PS-HI + SEBS blends with higher SEBS content as globular structures.

The application of Taft-Hancock steric constants to the free-radical initiated copolymerization of N-alkylmaleimides with α-methylstyrene

SummaryThe rates of free-radical initiated alternating copolymerization of α-methylstyrene with N-alkylmaleimides (RMI) decrease in the following order: Me>Et>n-Pr≈n-Bu≈n-Hex>iso-Pr>tert-Bu. A linear relationship was established in the plots of log(kR/kMe) against polar substituent constants σ*, “true steric” factors ES and corrected steric factors ESC. The best fit was obtained in plots of log (kR/kMe) against σ* and ESC while a large scattering of results was observed in the plot of log(kR/kMe) against ES.