Macromolecular Chain Segments Research Articles

High-density polyethylene composite filled with red mud: effect of coupling agent on mechanical and thermal properties

ABSTRACT In this study, red mud (RM) was modified with titanate coupling agent (triisostearoyl isopropoxy titanate, KR-TTS), and then the modified RM was melted blending with high-density polyethylene (HDPE) to prepare HDPE-based composite. The action mechanism of KR-TTS on the properties of HDPE composites was analysed combining with the movement mode of polyethylene macromolecular chain segments. The entanglement and mechanical interlocking of long alkyl chains of titanate coupling agent and the polyethylene molecular chains occurs in modified RM/HDPE composite, reflected by fracture morphology within tension process. The stronger interface interaction results in a decrease of polyethylene molecular chain segments motion under external loading, externally expressed as higher tensile strength and tensile modulus as well as storage modulus. Meanwhile, KR-TTS imparts modified RM/HDPE composite with higher elongation at break of uniaxial tension and lower damping ratio. The impact strength presents an improvement from 5.62 kJ/m2 of RM/HDPE composite to 6.56 kJ/m2 of modified RM/HDPE composite due to stronger interface strength. And modified RM/HDPE composite appears higher thermal stability, attributed to better particles dispersion and higher interface adhesion. Differential scanning calorimetric analysis shows that with the addition of coupling agent, the melt enthalpy of modified RM/HDPE composite decreases, indicating a decrement in the crystallinity of polyethylene composites (from 70.2% of RM/HDPE to 63.1% of modified RM/HDPE), resulted from the retarded stacking speed of chain segments into the crystal lattice during crystal growth.

Influence of graphite particles in thermal properties of amylopectin/PVA-based hydrogels

The aim of the present work is to study the influence of graphite particles on the molecular structure of the hydrogel composed of amylopectin/poly(vinyl alcohol) hybrid matrix by thermogravimetric analysis, differential scanning calorimetry and dynamic mechanical thermal analysis techniques. Hybrid amylopectin/PVA hydrogels were prepared with and without particles, and their properties were measured. The results of the analyses showed that the presence of particles in the reaction medium decreased the formation of cross-links among macromolecular chain segments, modifying thermal and mechanical properties of hydrogel. Raman spectroscopy confirmed the obtaining of graphitic carbon particles. Besides, optical microscopy and atomic force microscopy showed a large distribution in particles dimensions.

X-Ray Structure and PMR Spectra of Polycaproamide Modified by a Polyfluorinated Alcohol

Effects on polycaproamide structure of a polyfluorinated alcohol immobilized on montmorillonite clay nanoparticles were studied using x-ray structure analysis and broad-line PMR spectroscopy. An exfoliated composite formed and caused the crystal and molecular structures of this heterochain polymer to reorganize. A composite based on the polyfluorinated alcohol changed the mobility of macromolecular chain segments and increased the fraction of planar trans-conformations.

Synthesis and characteristics of pectiniform polyurethane‐modified polycarboxylate at room temperature

ABSTRACTIn this article, modified polyurethane prepolymer was synthesized by segmental synthesis method using isophorone diisocyanate, hydroxyl‐terminated silicone, polyether glycol dimethylolpropionic acid as raw materials. After that, pectiniform polycarboxylate, of which side chains were in roughly the same polymerization degree and main chains were in different lengths, was synthesized at room temperature in initiation system of hydrogen peroxide, ascorbic acid, and persulfate. Moreover, influence of various factors on the synthesis of polyurethane‐modified polycarboxylate at room temperature was discussed in detail and optimal synthesis process was determined. Results showed that redox initiation system, increasing initiator and monomer concentration, and extending reaction time needed to be adopted to complete the reaction. However, when the reaction time was over 4 h, water reducing of polycarboxylate declined rapidly. In addition, it could be found in Fourier transform infrared spectrum analysis that the CC double bonds in acrylic acid were opened and polymerized, macromolecular chain segments were successfully connected to polyoxyethylene chain segment, and resulting polycarboxylic acid molecule contained hydroxy, carboxyl, methyl, ester group, and other groups. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45873.

X-ray investigations of proton irradiation induced structure development in polyester fibers

The role of proton irradiation on the structural changes in partially crystalline poly (ethylene terephthalate) (PET) fibres has been investigated using a wide-angle X-ray scattering (WAXS). Experimental data about the influence of the exposure dose and the irradiation conditions in the processes of destruction and crosslinking in the irradiated objects have been obtained. The structural changes and the packing density of the macromolecular chain segments of the poly (ethylene terephthalate) filaments irradiated with different doses have been analyzed. A mechanism of the structural reorganization initiated by the irradiation has been supposed on the basis of the changes in the geometry of the intensity distribution of the X-ray diffraction patterns of the studied objects.

EFFECT OF PROTON IRRADIATION ON THE STRUCTURE DEVELOPMENT OF POLYETHYLENE TEREPHTHALATE FIBERS

The influence of proton irradiation on the structural changes in partially crystalline poly(ethylene terephthalate) (PET) filaments has been investigated using a wide-angle X-ray scattering (WAXS). Experimental data about the role of the exposure dose and the irradiation conditions in the processes of destruction and crosslinking in the irradiated objects have been obtained. The structural changes and the packing density of the macromolecular chain segments of the polyethylene terephthalate filaments irradiated with different doses have been analyzed. A mechanism of the structural reorganization initiated by the irradiation has been supposed on the basis of the changes in the geometry of the intensive distribution of the X-ray diffraction patterns of the objects.

Temperature and frequency analysis of the dynamical visco–elastic properties of high–density polyethylene

The behaviour of the dynamical visco–elastic functions in high–density polyethylene (HDPE), which carries the trade mark 'Bulen', in the region of gamma and beta relaxation transitions was studied. The method of forced torsion vibrations was used to obtain curves for the storage modulus (G′), loss modulus (G2) and loss tangent (tg δ) in the temperature interval (–180 to +20)°C and torsion frequency (0.1 to 100) rad/s. The maximum values of the storage modulus, the temperature at which these maximums appear and the full width at half maximum show an increase with the increase in the torsion frequency, but the most outstanding and prominent change is in the interval (0.1 to 10) rad/s. This fact is explained with reference to the processes of the deformational orientation of the macromolecular chain segments leading to changes in the intensity of the anelastic intermolecular interactions, the frequency response of the kinetic elements responsible for the realization of the gamma relaxation transitions, etc. The analogical frequency dependencies, derived from the loss tangent curves, show that the greatest changes take place in the same frequency interval (0.1 to 10) rad/s, although certain differences can be seen, and some of them are explained by the greater sensibility of tg δ changes in the physical kinetics of the gamma transition. The specific region in PE characterizing the local minimum of the mechanical losses is also discussed.

EFFECT OF PROTON IRRADIATION ON THE STRUCTURE DEVELOPMENT OF POLYETHYLENE TEREPHTHALATE FIBERS

The influence of proton irradiation on the structural changes in partially crystalline poly(ethylene terephthalate) (PET) filaments has been investigated using a wide-angle X-ray scattering (WAXS). Experimental data about the role of the exposure dose and the irradiation conditions in the processes of destruction and crosslinking in the irradiated objects have been obtained. The structural changes and the packing density of the macromolecular chain segments of the polyethylene terephthalate filaments irradiated with different doses have been analyzed. A mechanism of the structural reorganization initiated by the irradiation has been supposed on the basis of the changes in the geometry of the intensive distribution of the X-ray diffraction patterns of the objects.

Intriguing crystallization behavior and rheological properties of radical-based crosslinked biodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate)

A series of branched/crosslinked poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] with changing gel fractions were obtained by adding small amounts of crosslinking agents dicumyl peroxide (DCP) and triallyl isocyanurate (TAIC). The thermal and rheological properties of the samples were investigated. The chain branches formed by adding a certain amount of DCP bring in not only excess free volume which enhanced the cold crystallization ability but also defective crystals which decreased the melting temperature. Additionally, the rheological properties of branched samples were improved compared with those of neat P(3HB-co-4HB). The most intriguing result was the crystallization behavior of crosslinked P(3HB-co-4HB). The crosslinks, acting as favorable nucleation sites, can enhance the crystallization nucleation rate markedly. However, too many crosslinks could impede the transportation of macromolecular chain segments during the crystallization, resulting in a decreased crystallization rate, and the final crystallinity of crosslinked P(3HB-co-4HB) was independent of the degree of crosslinking. Furthermore, due to the formation of a gel network, crosslinked biodegradable P(3HB-co-4HB) exhibited remarkable improvement in rheological properties than branched samples, extending its processing methods, like foaming and film blowing. Accordingly, the practical applications of this biosourced and biocompatible polymer can be widely achieved.

Energy and acid-base characteristics of the surfaces of polymeric modifiers for filled cellulose nitrate composites

The energy and acid-base characteristics of the surface of butadiene-nitrile (SKN-18, SKN-26, SKN-40) and urethane (SKU-8A, SKU-8TB) rubbers, and also of polyvinyl nitrate and polyvinyl butyral were determined. Butadiene-nitrile rubbers are characterized by the highest, and vinyl polymers, by the lowest free surface energy. The free surface energy of urethane rubbers has intermediate values. The results obtained show that the surface energy of the polymers is determined both by the chemical nature of functional groups located directly in the surface layer and by the macromolecular packing density. The surface acidity increases in the order polyvinyl butyral < polyvinyl nitrate < SKU < SKN. The nature of the surface of the polymers under consideration is determined by prevalence of certain acid-base sites of adhesion interaction as a result of conformational turns of macromolecular chain segments.

Structure-properties relationship of poly(ethylene terephthalate) wool-type fibres

Two PET wool-type fibres were studied for this research, i.e. a normal wool-type and a low-pilling modification. The structural morphology and crystalline orientation of the fibres were investigated by means of wide-angle x-ray scattering (WAXS), density measurements and infrared (IR) spectroscopy. The degree of crystallinity, crystallite orientation, apparent crystallite dimensions and micro-void system were determined by x-ray scattering. Birefringence measurements were used to study the average molecular orientation and the orientation of macromolecular chain segments in the amorphous regions. In addition, PET samples were conventionally dyed and the effect of the structure on colour was followed using colorimetry. Significant differences between the two PET wool fibre types were observed; i.e. crystallinity is higher for the standard PET wool fibre type, the crystallites are slightly larger and better oriented, long periods are larger, the orientation of molecular segments in non-crystalline phase is higher, and bigger voids are formed. The observed structure gives rise to fibres higher tenacity and higher bending stiffness.

Thermal analysis of the melting process of poly(trimethylene terephthalate) using FTIR micro-spectroscopy

Thermal spectra of poly(trimethylene terephthalate) (PTT) were collected over a temperature range of 40–250 °C by FTIR micro-spectroscopy. Based on the changes of absorbance ratio corresponding to characteristic groups in low and high vibration energy states, the apparent enthalpy differences of vibration energy states transformation (Δ H v) in the melting process have been calculated by van’t Hoff equation at constant pressure. In comparison with the values of Δ H v, the status of participation for the vibration mode of various characteristic groups in PTT macromolecular chain segments was analyzed. It was found that the vibration modes related to the trimethylene glycol unit (O–CH 2–CH 2–CH 2–O) of PTT behaved significant sensitivity and made prominent contribution in the melting process. By the summarization of corresponding data, it has shown that the melting course concerned amorphous phase began at as early as 218 °C, accompanied by the occurrence of crystallization to certain extent, and the ending point was at approximately 238 °C; whereas the melting course concerned crystalline phase began till 228 °C, with the top value of 238 °C, and ended at 242 °C. Besides, for the particular ordered arrangement of chain segments of aromatic polyesters in the melting course, FTIR analysis has provided a reasonable explanation on a molecular level.

Influence of pressure on ionic transport in amorphous electrolytes: Comparison between glasses and salt polymer complexes

Accurate conductivity measurements as a function of hydrostatic pressure (1 - 5000 bars) and temperature (20 - 150 ~ have been performed on a cationic inorganic glass and a cationic conducting polymer. In both cases, the conductivity decreases with increasing pressure and the variation of ln~ at constant temperature as a function of pressure gives straight lines with slopes which allow an "activation volume", AV*, to be obtained by the relationship (3lnt/bP)r = - (AV*/RT). In the case of silver metaphosphate glass, studied below its glass transition temperature, the activation volume (5 cm3.mo1-1) is temperature independent and equal to the molar volume of the silver cation. Since the transport mechanism implies a free energy barrier, this volume is a real activation volume, corresponding to the difference in volume between a mole of the moving species in its activated transition state and its volume at normal equilibrium. In the case of the sodium conductive polymer, studied above its glass transition temperature, the previous thermodynamic definition does not hold any more because the ionic transport follows a V.T.F. behaviour rather than an Arrhenius law. Consequently, AV* is an "apparent activation volume" without a simple physical meaning. Experimental values are higher (20 to 30 cma.mo1-1) and decrease with temperature. In this polymer, the mobility of the charge carriers is interpreted in terms of free volume mechanism. From the variations of the apparent activation volume with temperature, the critical free volume Vf* for an elementary displacement is estimated. For the Na + conductive ionomer Vf* is estimated to be equal to 13 cm3.mol 1. This large value would indicate the participation of macromolecular chain segments in the ionic transport.

The macromolecular nature of bituminous coal

Considerable insight into the macromolecular state of coal has been obtained by examining the optical anisotropy of untreated solvent-swollen, and chemically derivatized thin sections of coal. From the effect of pressure on the optical anisotropy, and from the rate and degree of recovery after release of pressure, it was found possible to determine whether the coal is in a plastic or rubbery state, whether a rubbery state is cross-linked and how mobile the macromolecular chain segments are. The experimental technique utilized for this work was transmission optical microscopy in polarized light of uncontaminated thin sections of vitrinite from a bituminous coal. The study included in-situ microscopic examination of swollen coal immersed in pyridine, THF, toluene and several other solvents. Some samples were O-methylated to assess the impact of hydrogen bonding. New results and conclusions derived from this study include: (1) the vitrinite of raw bituminous coal is a plastic macromolecular substance; (2) coal swollen in pyridine (and some other ‘specific’ solvents) is a cross-linked rubber and its macromolecular chain segments have substantial mobility; (3) when pyridine-extracted coal dries, it reverts to a plastic; (4) the large discrepancies previously found between values of M c (molecular weight between crosslinks) measured by solvent-swelling and by stress-strain techniques is caused by differences in secondary interactions; (5) various solvents can, by their effect on secondary interactions, create appreciably different macromolecular structures in the coal; (6) different solvents, depending on their effect on secondary interactions in the coal, can be expected to extract chemically different molecules from a coal - rates of extraction and the ability of solvents to extract larger molecules should also differ; (7) O-methylated coal is a plastic, and thus, in addition to hydrogen bonding, other secondary interactions are of great importance; (8) it is likely that in their dry condition, solvent-treated coal and O-alkylated coal, as well as untreated coal, are in glassy states; (9) pyridine by itself appears to relax substantially all secondary interactions which are weakened by O-methylation, only permanent bonds are not relaxed; (10) previous measurements of M c can now be reassessed in view of these results.

The macromolecular states of solvent-swollen and dry coal

Improved understanding of the physical state of coal is needed to better characterize, modify and utilize this abundant source of energy. In spite of extensive research in this area for well over half a century, the level of understanding has been poor. Here, new substantive evidence clarifying the macromolecular states of coal is presented. The approach involved studying changes in the optical anisotropy of raw and solvent-swollen thin section samples of a bituminous coal. It was found that the natural optical anisotropy was completely relaxed on immersion of the coal in pyridine. From changes in the optical anisotropy induced by pressure, the solvent-swollen coal was determined to be a cross-linked rubber and its macromolecular chain segments were found to have substantial mobility. It appears that pyridine and some other good swelling agents relax essentially all of the secondary bonding in the coal. On the other hand, raw coal and coal immersed in water, various hydrocarbon solvents and other poor swelling agents were determined to be macromolecular plastics.