Surface migration of the carboxylic acids (C 10 H 21 COOH, C 11 H 23 COOH, C 12 H 25 COOH, C 15 H 31 COOH, C 16 H 33 COOH, and C 17 H 35 COOH) in styrene-butadiene rubber (SBR) matrix was investigated together with its influence on tribological properties of the vulcanisates. Macro-and microtribological properties were correlated with properties that come from carboxylic acid addition to the samples. A plastifying effect was characterized by a decrease of the rubber glass transition temperature measured by the DSC method. Thickness of an acid bloom was directly determined from an indentation experiment and estimated from the DSC curve as well as from FTIR reflection spectra. Morphology of the bloom was studied using an AFM technique to characterize topography as well as microroughness of the bloom surface. Macrofriction was studied using block-on-ring tribometer. Microfriction was examined with a Nano Test apparatus, applying ball-on-plate contact. Despite correlation found between plastification, morphology, and bloom thickness on the one hand, and tribologic properties of the rubber on the other hand, influence of the chain length of carboxylic acids on properties of the samples still needs further qualitative investigation. Tribological properties of SBR modified with carboxylic acids are the result of balance of two opposite effects: plastification of rubber-leading to an increase of friction and lubrication-which causes a decrease of friction of the rubber. Apart from plastifying and lubrication effects microroughness also plays an important role in friction.
Streszczenie -Przedstawiono wyniki badañ dotycz¹cych strukturalnych aspektów modyfikacji kauczuku butadienowo-styrenowego (SBR) polimetylowodorosiloksanami (PMHS) i polidimetylosiloksanami (PDMS). Modyfikatory te ró¿ni³y siê reaktywnooeci¹, mierzon¹ ilooeciowym stosunkiem merów metylowodorosiloksanowych do merów dimetylosiloksanowych. Okreoelono wp³yw reaktywnooeci modyfikatora na kinetykê rodnikowej reakcji sieciowania kauczuku wobec ditlenku dikumylu (DCP) a tak¿e wulkanizacji siarkowej. W przypadku zastosowania DCP szybkooeae i wydajnooeae sieciowania rosn¹ wraz ze zwiêkszaniem reaktywnooeci u¿ytego modyfikatora, natomiast w wulkanizacji siarkowej najwiêksz¹ szybkooeci¹ reakcji odznacza³y siê uk³ady zawieraj¹ce najmniej reaktywny PMHS. Nie zaobserwowano równie¿ ¿adnego wp³ywu modyfikatora na wydajnooeae wulkanizacji siark¹ i wyjaoeniono przyczyny tego zjawiska. Sieciowaniu wobec DCP towarzysz¹ reakcje szczepienia PMHS na elastomerze oraz jego polimeryzacji w kauczukowej matrycy. Modyfikatory krzemoorganiczne przejawiaj¹ tendencjê do migracji i segregacji powierzchniowej w kauczuku. Obok zmiany morfologii uk³adu, wp³ywa to na w³aoeciwooeci mechaniczne i trybologiczne usieciowanego SBR. Mianowicie, wprowadzenie modyfikatora powoduje zmniejszenie wytrzyma³ooeci na rozci¹ganie, zw³aszcza w przypadku kauczuku usieciowanego wobec DCP. Wspó³czynnik tarcia wulkanizatów siarkowych zwiêksza siê pod wp³ywem modyfikacji, natomiast w przypadku SBR usieciowanego za pomo-c¹ DCP mo¿na zmniejszyae ten wspó³czynnik u¿ywaj¹c do modyfikacji PDMS lub PMHS o ma³ej reaktywnooeci. S³owa kluczowe: kauczuk butadienowo-styrenowy, polimetylowodorosiloksany, polidimetylosiloksany, modyfikacja, sieciowanie, morfologia, wytrzyma³ooeae mechaniczna, energia powierzchni, tarcie. MODIFICATION OF STYRENE-BUTADIENE RUBBER WITH POLYMETHYLSILOXANESSummary -The results of investigations on structural aspects of styrene-butadiene rubber (SBR) modification with polymethylhydrosiloxanes (PMHS) or polydimethylsiloxanes (PDMS) were presented. The modifiers varied in reactivity, measured as a ratio of methylhydrosiloxane and dimethylsiloxane units ( Table 1). The effects of modifier reactivity on the kinetics of radical reaction of rubber curing in the presence of dicumyl peroxide (DCP) as well as on the sulfur-induced vulcanization were determined (Table 2-5, Fig. 2 and 3). In case of DCP use the curing rate and efficiency increase with increasing reactivity of modifier used. However, in case of sulfur-induced vulcanization the systems containing less active PMHS showed the highest reaction rate. No modifier effect on the efficiency of sulfur-induced vulcanization was observed. It can be the result of active complex blocking by polysiloxanes, wetting the surface of ZnO being an activator of sulfur curing system. The curing in the presence of DCP is accompanied with the reactions of PMHS grafting onto elastomer and its polymerization in the rubber matrix. Organosilicon modifiers show the tendency to surface migration and segregation in the rubber. Togethe...
The activity of iodoform (CHI 3 ) toward unsaturated rubbers was examined. Special attention was devoted to cis-1,4-(poly)isoprene (IR). The thermal decomposition of CHI 3 was studied by ion mass spectroscopy, and the obtained data were used for the identification of pyrolysis products of CHI 3 vulcanizates by pyrolytic gas chromatography. The kinetics of the chemical crosslinking of rubber were studied with a cure meter. The changes observed in the chemical structure of rubber were explained on the basis of 13 CNMR and Fourier transform infrared spectroscopy, differential scanning calorimetry, equilibrium swelling, and chemical microanalysis data. Apart from crosslinking, a simultaneous modification of the rubber macromolecules took place, specifically the cistrans isomerization of IR. This resulted in a significant increase in the rubber hardness, especially after a postheat treatment accompanied by oxidation. CHI 3 -IR vulcanizates behaved like thermoplastics because of the presence of a trans-1,4 phase, as confirmed by dynamic mechanical thermal analysis. The structure of the macromolecules treated with CHI 3 and its effect on the physical properties of the material were compared with those of peroxide-IR vulcanizates. The influence of the modification on the surface energy, bacteriostaticity, and mechanical properties of the vulcanizates was examined.
The surface layer of polymers exhibits different composition, morphology and structure, also in the nanoscale, from the bulk material. The paper demonstrates the clearest examples, discussing consequences of the gradient nature of the materials from the aspect of their exploitation (mainly hardness profile and friction). The ability of low molecular weight substances to migrate in a polymer matrix and the surface segregation occurring in polymer blends, are studied by FTIR, AFM, XPS, microindentation, microfriction, contact angle and DSC techniques. It has been proved that the surface layer of polymer materials can be shaped during both compounding and processing.
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