Yu. A. Olkhov

Thermomechanical study of molecular and topological structure of different kinds of sulfur

A novel method is used to study topological and molecular structure of different kinds of sulfur (mineral and two polymeric types). It is based on thermomechanical analysis of solid (not dissolved) polymer. It was found that a deep difference in their molecular weight distributions and in their crystallinity degrees exist. Both mineral and polymeric sulfur have polymer nature.

Thermomechanical study of low-density polyethylene, polyamide 6 and its blends

Abstract By using thermomechanical analysis (TMA) multiple relaxation transitions in the amorphous part of semi-crystalline polymers and their blends can be found. These result from differences in the interaction energies between segments of macromolecules, and as a result, in molecular mobility. TMA shows essential changes in the structure of low-density polyethylene (LDPE) resulting from the grafting of a maleic anhydride (LDPE-g-MAH) onto this semi-crystalline polymer. The grafting process did not suppress the ability of polyethylene to crystallize. Essential changes were found in molecular weight distribution and relaxation transitions of the ternary blends LDPE/PA6 (polyamide 6, PA6)/LDPE-g-MAH studied. For a concentration of PA6 up to 30 wt.%, a single relaxation transition is visible, which testifies that the components are miscible in the amorphous region. For blends with 40 and 50 wt.% of PA6, this structure was transformed and two relaxation transitions are visible. From the results obtained in this study it is concluded that the introduction 5 wt.% of grafted polyethylene is sufficient to produce a PA6/LDPE blend only for PA6 concentration up to 30 wt.% which is homogenous on “molecular” level. The transformation of the structure of the ternary polymer blend was explained by the interaction of the components during the melt mixing and changes in the structure of its amorphous regions.

Application of thermomechanical mass spectroscopy for analysis of molecular and topological structure of rubber

A novel method was applied to study the topological and molecular structures of multicomponent rubber. This method is based on the thermomechanical analysis of a solid polymer. A diblock amorphous structure was found for the studied rubber network. These blocks differ a great deal in their glass transition temperature. The methodology of how to calculate the crosslink density in each block, the molecular weight distribution of the chains between the junctions of the network, and the shares of low-temperature (soft) and high-temperature (hard) blocks in a structure of the rubber network were also shown. Based on these data it is possible to calculate the number-average and weight-average molecular weight and the polydispersity coefficients of the chains between the junctions of the network.

Thermomechanical study of butyl rubber mastication during compounding

A thermomechanical method was used to study the topological and molecular structure of model rubber compounds. This structure changes because of mastication during compounding. It was found that raw butyl rubber has a diblock structure. The molecular weight distribution of the chains between the junctions of the polymer network, the coefficient of polydispersity, a share of low-temperature and high-temperature blocks, and changes in their glass transition temperatures as a result of the mixing of butyl rubber depend on both the presence of sulfur and the kind of sulfur (polymeric or mineral).

Effect of gamma-irradiation on morphology of copolymer of tetrafluoroethylene with hexafluoropropylene as revealed by thermomechanical analysis and radiothermoluminescence

The morphologies of different commercial forms of the copolymer of tetrafluoroethylene with hexafluoropropylene (FEP) were investigated by thermomechanical analysis. Both granules and powders of FEPs have similar morphologies, but different temperatures for phase transitions. Irradiation reduces the crystallinity of the FEPs and results in a transformation from the crystalline to the amorphous form. After heating of various forms of FEP irradiated at 77 K, there are three intense maxima of radiothermoluminescence in the temperature ranges: 150–144, 174–167, and 210–206 K. The nature of the radiothermoluminescence and the phase transitions of the FEPs as a result of gamma—irradiation are discussed.

Study of butadiene rubber mastication and mixing with carbon black

A thermomechanical method was applied to study the topological and molecular structure of SKD butadiene rubber masticated and mixed with carbon black. Triblock structure (two amorphous blocks and one a pseudocrystalline structure) of a studied raw rubber and rubber compound networks were found. A ratio of these morphology structures changes during mastication. After mastication, a low-temperature block has two glass transition temperatures that shows its more complex structure than that in raw rubber. This shows deep transformations taking place during the mastication process. Despite applying high shear forces and heating during mixing with carbon black in a filled BR compound, we present three structures characteristic for BR. However, introduction of carbon black changes the topological structure of polybutadiene. A part of both amorphous blocks grows. A part ofa crystalline structure lowers from 88% after 2.5 min of mixing to 54% after 20 min of compounding. The molecular weight distribution of the chains between the junctions of the network and parts of low-temperature and high-temperature amorphous blocks, and pseudocrystalline structures in architecture of the rubber network were also calculated.

The Formation of the Polyisocyanurate Networks Structure

Abstract The reactions of PCT and CPCT of aliphatic isocyanates in the presence of catalysts HBSO and CN-DMSO were found to obey the first-order law. The observed rate constants at various temperatures and catalyst concentrations, the activation energy were determined. It was shown that in the PCT process with above catalysts practically only one type of a cyclic structure (isocyanurate) was formed. The HMDI PCT gives a highly cross-links polymer, the cross-links density of a network being equal to v = 26 × 10−4 mol/cm3. In CPCT the polyisocyanurates with various cross-links density of a polymer network were obtained. At different ratios of mono- and diisocyanate the molecular-mass parameters of the interunit chains were determined, their effect on physico-mechanical properties of polyisocyanurates was established.

On a structure of NR and BR carbon black filled rubber compounds and vulcanizates

Rubber compounds containing natural rubber (NR) filled with carbon black were investigated with the help of the thermomechanical method according to the procedure described in a previous article (Jurkowska et al. J Appl Polym Sci, in press). It was stated that NR filled with carbon black has two amorphous blocks differing in the transition temperatures and one pseudo-crystalline structure. A ratio of these morphology structures changes during mixing with carbon black depending on the carbon black content and mixing time. A crystalline structure has two or three temperatures characterizing the beginning of melting and the beginning of flow. This evidences its complex architecture. Vulcanized rubber of NR mixed with butadiene rubber (BR) in a ratio of 70/30, filled with carbon black, has two-block amorphous structure without a pseudo-crystalline structure. A dynamics of forming molecular and topological structures of vulcanizates depends on carbon black content.

Comparative TMA and NMR investigation of a structure of carbon-black-free cured butadiene rubber

Abstract Butadiene rubbers (BRs) differing in isomeric content and cured with different amounts of dicumyl peroxide (DCP) have, according to TMA investigations, regions with two glass transition temperatures (low and high) and different thermal expansion properties. BR network has chemical and cluster type (physical localised) branching junctions. For rubbers of the same isomeric content, shares of such regions depend on concentration of DCP. This fact suggests cis–trans isomerization at curing, which increases the content of a high-temperature region with predominantly chemical branching junctions, because cluster type branching junctions start to relax at T g ″. It is supposed that an essential change in T g , if DCP concentration in the rubber compound is varied, is determined by the different molecular mobility of the chains included in associated structures of cluster junctions of a network of cured rubber. Such mobility also increases if 1,2 (vinyl) isomer is present in the BR chain. The latter is probably distributed uniformly between the chains of both regions. In a low-temperature region it could act as an antiplasticizer, whereas in a high-temperature region as a plasticizer. The molecular weight distribution of the chains between the junctions of a low-temperature region is virtually bimodal for low DCP concentration in rubber compounds. This could result from some zones with different crosslinking degree within the network. It is believed that this region has branching junctions, which are of a low crosslink density of chemical types and a high crosslinking density of cluster type junctions. A wide spectrum of isomeric content in neat and cured BR when a medium content of DCP was used meant that a low-temperature region had unimodal and symmetric MWD between the junctions. In a high-temperature region the exact opposite phenomenon may be observed — separation of chain segment length giving a bimodal MWD. A possible reason for this is non-uniform distribution of 1,2 (vinyl) isomer within the chains of a high-temperature region. The shift in MWD between the junctions from bimodal to unimodal as DCP content is raised, which was identified using TMA, confirms our 2 H NMR findings. The two splits in the 2 H NMR spectra observed at lower DCP contents could result from regions with different crosslink density, as we have argued in a recently published paper. All these conclusions confirm the applicability of the adopted TMA for testing a complex structure of rubbers.

Influence of mixing procedures and curing time on molecular and topological structures of NR/BR vulcanizate

A rubber compound containing butadiene rubber (BR), natural rubber (NR), and carbon black was investigated by thermomechanical analysis (TMA). A difference in dynamics of the formation of molecular and topological structures of a vulcanizate were found to be dependent on the mixing technology and curing time. Separation of the topological structure of cured rubber into two blocks with differing transition temperatures was visible after 20 min of vulcanization, when a share of a low-temperature block is minimal and M n(n) reaches a stable value of about 2400. A low-temperature block had a predominant concentration of covalent branching junctions, independent of the mixing procedures, whereas the high-temperature block had covalent and topological junctions in concentrations that were dependent on the mixing method. For curing times longer than 20 min, the characteristic changes in values of M n(n) are dependent on the procedure of rubber compound mixing. After additional homogenization of compounds and vulcanization, the rubbers are characterized by a diblock structure with the same qualitative structure of the branching junctions as for nonhomogenized ones. In some cases, the homogenization increases the relative concentration of the covalent junctions in the high-temperature block, when a preblend of BR and carbon black was prepared first, and then mixed with NR, this technology makes rubber compounds less sensitive to additional homogenization during further processing. A mechanism of creation and transformation of rubber-carbon black junctions during compounding and vulcanization of rubber compounds with two raw rubbers that differed in adsorption ability was proposed.