Macromolecular Segments Research Articles

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.

Driving the self assembly of gold nanoparticle structures using highly oriented PTFE templates

We present a non-conventional, low cost and simple approach for patterning gold nanoparticles (NPs) using highly oriented PolyTetraFluoroEthylene (HOPTFE) macromolecular segments on glass substrates. Transparent and stable HOPTFE templates for NP self-assembly were prepared by sliding unidirectionally a PTFE rod across a glass substrate at a fixed temperature with a constant pressure. Gold NPs, 50 nm nominal core diameter stabilized by citrate and octanethiol, have been assembled onto HOPTFE macromolecular segments using two different procedures. The first method is based on the drop casting of octanethiol capped NPs to obtain a growth of 1-D structures onto HOPTFE ridges. The second method exploits the functionalization of the glass substrate using (3-Aminopropyl)-triethatoxysilane (APTES) in order to induce the formation of 2-D structures between HOPTFE ridges. The self organized nanostructures and their morphological features have been investigated using AFM. The core size distribution of gold NPs was analyzed from TEM images.

Orientation Kinetics of Screw-Axial Vibration on Glass Fiber Reinforced Polypropylene Composites

Glass fibers oriented with melt flow direction in a vibrational force field perform better than those in steady-state flow fields in a mathematical model of glass fiber orientation in a vibrational force field. From a molecular perspective, the instantaneous impulse and local negative pressure of the macromolecular chains and chain segments generated by vibration accelerate melting, reaching the physicochemical equilibrium. Afterward, the composite samples are scanned with a scanning electronic micrograph to compare reality with statistical analyses of glass fiber orientation, tensile testing, and impact testing. The results indicate that this model enables the prediction of processing and design parameters in the injection molding, from which optimum conditions for polymer design and processing can be discovered.

Preparation and properties of natural rubber nanocomposites with solid‐state organomodified montmorillonite

AbstractA novel organomodified montmorillonite prepared by solid‐state method and its nanocomposites with natural rubber were studied. The nanocomposites were prepared by traditional rubber mixing and vulcanizing process. The properties of solid‐state organomodified montmorillonite were investigated by Fourier‐transform infrared spectroscopy (FITR) and thermogravimetric analysis (TGA). The dispersion of the layered silicate in rubber matrix was characterized by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that the nanocomposites consisting of solid‐state organomodified montmorillonite and natural rubber are obtained. The solid‐state organomodified montmorillonite can not only accelerate the curing process, but also improve the mechanical and aging resistance properties of NR. The properties improvement caused by the fillers are attributed to partial intercalation of the organophilic clay by NR macromolecules. In addition, the dynamic mechanical analysis (DMA) results showed a decrease of tanδmax and increase of Tg when the organoclay is added to the rubber matrix, which is due to the confinement of the macromolecular segments into the organoclay nanolayers and the strong interaction between the filler and rubber matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Insight into the Origin of the Thermosensitivity of Poly[2‐(dimethylamino)ethyl methacrylate

We investigate the effects of pH and temperature on the conformational changes of poly[2-(dimethylamino)ethyl methacrylate] (PDEM) chains at the air/water interface by using Langmuir balance and sum frequency generation vibrational spectroscopy. At pH 4, the tertiary amine groups are fully charged and the PDEM chains are so hydrophilic that they completely enter into the water phase and do not exhibit thermosensitivity. At pH 7, these groups are only partially charged, and the accompanying hydration/dehydration--followed by repartitioning into the water and air phases--gives rise to a marked thermosensitivty. Finally, at pH 10, the tertiary amine groups become uncharged and thus preferentially stay in the hydrophobic air phase, devoid of associated water molecules, which results in the surface-pressure change (DeltaPi) being nearly independent of the temperature. Our Langmuir-balance experiments, coupled with surface-sensitive spectroscopy, demonstrate that: 1) the thermosensitivity of the PDEM chains relates to the hydration/dehydration of the tertiary amine groups, 2) the phase transition of thermosensitive polymers is most likely initiated by the dehydration of the chains, and 3) the phase transition of thermosensitive polymers at the air/water interface is markedly different from that in aqueous solution because of the redistribution of the macromolecular segments induced by the asymmetric forces at the air/water interface.

Influence of Flame Retardant and Glass Fibre on Non-Isothermal Crystallisation Behaviour of Pa66

The authors studied the influence of melamine polyphosphate flame-retardant (MPP-FR) and glass fibre on the non-isothermal crystallisation behaviour of a polyamide (PA66) by differential scanning calorimetry (DSC). The glass fibre reinforced PA66 (PA66/GF) and its reinforced flame retarded equivalent (PA66/GF/FR) were prepared using a twin-screw extruder. The experimental results demonstrated that the MPP-FR increased the crystallisation rate and decreased the supercooling required for crystallising nucleation. The glass fibres increased the crystallisation rate and the amount of supercooling. Avrami analysis showed that the non-isothermal crystallisation of PA66 and its composites followed the Avrami equation. The activation energy for the transport of macromolecular segments to the growing surface was calculated by using the Kissinger method based upon DSC data, and the calculated activation energies were 243.5 kJ·mol−1, 201.1 kJ·mol−1 and 305.9 kJ·mol−1 for PA66, PA66/GF and PA66/GF/FR, respectively. The activity of nucleation for GF and MPP-FR were 0.87 and 0.79 respectively, calculated by Dobreva's method. The results indicate that the MPP-FR has more effective ability to promote heterogeneous nucleation than GF.

Crystallization kinetics of impact modified polypropylene

Non-isothermal crystallization kinetics of PP homopolymer (PPHP), PP copolymer (PPCP) and nucleated PP copolymer (PPCPN) were studied using differential scanning calorimetry (DSC) at different cooling rates. Various kinetic models, namely, Avrami equation modified by Jeziorny, Ozawa method and the method developed by Mo were employed to describe non-isothermal crystallization kinetics of the samples. The Ozawa analysis failed to provide an adequate description of the crystallization process; however, the method developed by Mo was successful in describing the non-isothermal crystallization of PP samples. Different kinetic parameters such as Avrami exponent n, kinetic crystallization rate constant kc, another kinetic parameter F(T), crystallization temperature Tc, half life of crystallization t1/2 etc. were determined at various cooling rates. The difference in the values of Avrami exponent n in PPCPN indicated a heterogeneous nucleation and tridimensional spherulitic growth, whereas both PPHP and PPCP showed different nucleation and growth trends. The values of t1/2, kc and F(T) showed that in all samples crystallization rate increased with increase in cooling rate. Moreover, the crystallization rate of PPCPN was faster than that of other two samples at a given cooling rate. The activation energy for the transport of macromolecular segments to growing crystal surface was determined by using the Kissinger method. The lowest activation energy (ΔE) of PPCPN indicated a highest crystallization tendency than that of other two samples.

Crystallization behaviors of linear and long chain branched polypropylene

AbstractThe nonisothermal crystallization kinetics of linear and long chain branched polypropylene (LCB PP) were investigated by differential scanning calorimetry (DSC) at various cooling rates. Several methods such as Avrami, Ozawa, and Jeziorny were applied to describe the crystallization process of linear PP and LCB PPs with different LCB level under nonisothermal conditions. The values of t1/2, Zc, and F(T) show that LCB has the role of heterogeneous nucleating agent and accelerates the crystallization process of PP. Moreover, the Kissinger method was used to evaluate the activation energy of linear PP and LCB PPs. The result shows that the activation energy of LCB PPs are higher than that of linear PP, indicating that the presence of LCB baffles the transfer of macromolecular segments from PP melt to the crystal growth surface. Furthermore, the crystal morphology of linear PP and LCB PPs was observed through polarized optical microscopy (POM), and fine spherulites were observed for LCB PPs. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3592–3600, 2007

Influence of maleic anhydride-grafted EPDM and flame retardant on interfacial interaction of glass fiber reinforced PA-66

In this paper, the effects of melamine polyphosphate flame retardant (MPP-FR) and maleic anhydride-grafted EPDM (MA-EPDM) on the interfacial interaction of PA66/GF were investigated by means of scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), rheological behavior and mechanical properties. The experimental results demonstrate that MPP-FR and MA-EPDM could effectively improve interfacial interactions between the PA66 and GF. Based on SEM, good interfacial adhesion between PA66 and GF in PA66/GF/FR and PA66/GF/FR/MA-EPDM composites was observed, however, MPP-FR destroyed the PA66 matrix. DMA results show that MPP-FR increased glass transition temperature ( T g) and storage modulus, and lower tan δ, while MA-EPDM showed a little effect on them in PA66/GF/FR/MA-EPDM composite compared with PA66/GF/FR. MPP-FR made PA66 crystallization temperature and the activation energy of the macromolecular segments transport increase clearly, and enhanced crystallization degree of PA66 according to DSC results. These results demonstrate MPP-FR presented the nucleate effect for the crystallization of PA66. At the low shear rate, MPP-FR and MA-EPDM obviously enhanced apparent viscosities of the composites. This is attributed that MPP-FR improved the interfacial interaction of the composites, and MA-EPDM promoted the formation of high molecular weight structures by the reactions between MA and amine groups. All results in this paper were consistent, and showed the good interaction among PA66, GF, MPP and MA-EPDM, which were proved by the mechanical properties of the composites.

Effect of solvent nature on the optical anisotropy of poly(1-trimethylsilyl-1-propyne) molecules

The optical properties of poly(1-trimethylsilyl-1-propyne) solutions in solvents possessing optical anisotropy have been studied with dynamic birefringence measurements. In solvents characterized by refractive indexes different from the refractive index of a dry polymer, the optical form effect has been discovered. This effect is determined by the shape asymmetry of a macromolecular segment and its rigidity. Estimates showed that the length of the statistical segment, which characterizes the thermodynamic rigidity of the macromolecular chains under study, is 82 × 10−8 cm. The shear optical coefficient for solutions of the test polymer in an anisotropic solvent is markedly higher than the corresponding value in an isotropic solvent. This difference is related to the orientation of anisotropic solvent molecules along the main chain of a macromolecule by their highest polarizability axis. Under the assumption that the orientational order of solvent molecules relative to chain macromolecules is independent of the thermodynamic rigidity of chain molecules, the size of the statistical segment of the macromolecules in question has been independently estimated as 98 × 10−8 cm.

Nonisothermal crystallization kinetics of poly(butylene terephthalate)/montmorillonite nanocomposites

AbstractThe melt intercalation method was employed to prepare poly(butylene terephthalate) (PBT)/montmorillonite (MMT) nanocomposites, and the microstructures were characterized with X‐ray diffraction and transmission electron microscopy. Then, the nonisothermal crystallization behavior of the nanocomposites was studied with differential scanning calorimetry (DSC). The DSC results showed that the exothermic peaks for the nanocomposites distinctly shifted to lower temperatures at various cooling rates in comparison with that for pure PBT, and with increasing MMT content, the peak crystallization temperature of the PBT/MMT hybrids declined gradually. The nonisothermal crystallization kinetics were analyzed by the Avrami, Jeziorny, Ozawa, and Mo methods on the basis of the DSC data. The results revealed that very small amounts of clay (1 wt %) could accelerate the crystallization process, whereas higher clay loadings reduced the rate of crystallization. In addition, the activation energy for the transport of the macromolecular segments to the growing surface was determined by the Kissinger method. The results clearly indicated that the hybrids with small amounts of clay presented lower activation energy than PBT, whereas those with higher clay loadings showed higher activation energy. The MMT content and the crystallization conditions as well as the nature of the matrix itself affected the crystallization behavior of the hybrids. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3257–3265, 2006

Morphology, thermal and mechanical behavior of polypropylene nanocomposites toughened with poly(ethylene‐co‐octene)

AbstractRubber‐toughened polypropylene (PP) nanocomposites containing organophilic layered silicates were prepared by means of melt extrusion at 230 °C using a co‐rotating twin‐screw extruder in order to examine the influence of the organoclay and the addition of PP grafted with maleic anhydride (PPgMAH) as a compatibilizer on the morphological, mechanical and thermal properties. The mechanical properties of rubber‐toughened polypropylene nanocomposites (RTPPNCs) were studied through tensile, flexural and impact tests. Scanning electron microscopy (SEM) was used for investigation of the phase morphology and rubber particles size. X‐ray diffraction (XRD) was employed to characterize the formation of nanocomposites. The thermal properties were investigated by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The dynamic mechanical properties were examined by using dynamic mechanical analysis (DMA). From the tensile and flexural tests, the optimum loading of organoclay in RTPP was found to be 6 wt%. The optimum loading of PPgMAH, based on the tensile and flexural properties, was also 6 wt%. The increase in the organoclay and PPgMAH content resulted in a severe embrittlement, manifested by a drop in the impact strength and tensile elongation at break. XRD studies revealed that intercalated RTPPNCs had been successfully prepared where the macromolecular PP segments were intercalated into the interlayer space of the organoclay. In addition, the organoclay was dispersed more evenly in the RTPPNC as the PPgMAH content increased. TGA results revealed that the thermal stability of the RTPPNC improved significantly with the addition of a small amount of organoclay. Copyright © 2006 Society of Chemical Industry

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.

Solvent and molecular weight effects on fluorescence emission of MEH-PPV

Here we systematically studied the excitation and the fluorescence steady-state spectroscopy of poly(2-methoxy-5(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) with three molecular weights, Mn= 51 kg mol-1, Mn= 86 kg mol-1 and Mn= 125 kg mol-1, in two equally good solvents and several concentrations, from dilute solutions to solid-state films produced by casting. The appropriateness of the two solvents was established by comparing their solubility parameters and the solubility parameter of the MEH-PPV estimated using the Small, the Van Krevelen and the Hoy models. Thus, chloroform and toluene were chosen. Fluorescence spectra were recorded for solutions in several concentrations (10-8 mol L-1 to 10-4 mol L-1) and films produced by casting, showing that chloroform and toluene solvate the polymer chain differently. Diluted solutions (10-8 mol L-1) in chloroform exhibit broader fluorescence spectra. A red-shift of the fluorescence spectra was observed for concentrations higher than 10-6 mol L-1 that can be explained using Kasha's rule for the sandwich anti-parallel orientation of the transition moments of the two chromophores. The conformations observed in solutions are partially retained in the solid films in addition to the broader red-shift spectra attributed to aggregated forms of the macromolecular segments. Annealing of the polymer films at the glass transition temperature eliminates the more stressed conformations, erases the memory and leads to sharper fluorescence spectra.

Tribological Behavior of Polymers Simulated by Molecular Dynamics

Using molecular dynamics to simulate behavior of polymer surfaces during scratch testing, we report the first results of computer simulations of scratch behavior of noncrystals. A previously described procedure for creating realistic polymeric materials on the computer [W. Brostow, A.M. Cunha, and R. Simoes, Mater. Res. Innovat. 7, 19 (2003)] and used until now to simulate mechanical behavior of metals [S. Blonski, W. Brostow, and J. Kubat, Phys. Rev. B 49, 6494 (1994)] and one- and two-phase polymers [W. Brostow, A.M. Cunha, J. Quintanilla, and R. Simoes, Macromol. Theory Simul. 11, 308 (2002); W. Brostow, A.M. Cunha, and R. Simoes, Proc. Ann. Tech. Conf. Soc. Plastics Engrs. 60, 3105 (2002)] was applied. While experiments provide only the macroscopic penetration depth and the recovery (healing) depth, the simulations give the behavior of each macromolecular chain segment at each moment in time. We report results for one-phase polymers and also for systems with varying concentrations of a liquid crystalline (LC) second-phase that acts as a reinforcement. We relate the local structure to scratch resistance and recovery. The orientation of the chemical bonds is a major factor. The presence of a LC phase improves the tribological properties; however, the effect is not as significant as might have been expected.

Dynamics of hyperbranched polymers and dendrimers: theoretical models

AbstractChemical reactions depend in many ways on the dynamics of the underlying reactants, and an important aspect is the distance covered by the reactants before the reaction act occurs. Hence, even diffusion‐limited reactions between point particles in confined geometries and in low‐dimensional systems display decay forms which are very different from those obtained from simple chemical kinetics. Clearly, even more complex decay forms hold for macromolecules, given their internal degrees of freedom. Here we discuss how the dynamics of macromolecules in solution relates to their topological structure and focus on the motion of macromolecular segments (monomers) under the influence of external fields. After a general survey of the method of generalized Gaussian structures (GGS) we recall the wealth of forms which are observed, depending on the topology and on the microscopic dynamics involved. Paradigmatic are the findings for the class of hyperbranched macromolecules; to these belong the dendrimers. While the dendrimers do not show a typical scaling behavior, as found, say, for linear chains, the situation is different for particular classes of regular hyperbranched polymers which are fractal. We end by discussing their pattern of motion in the GGS‐Rouse‐Zimm picture.

Viscous Flow and Plastic Deformation of Glasses in the Model of Excited Atoms

The critical displacement of an atom (a group of atoms) Δrmax, which corresponds to the interatomic interaction force at the maximum, is treated as the atomic excitation in liquids and glasses. The formation and migration of excited atoms are governed by local fluctuations of the configurational entropy. In amorphous linear polymers, the role of an excited kinetic unit is played by a small-sized macromolecular segment (an atomic group in a monomer). The atomic excitation in silicate glasses corresponds to the critical displacement of a bridging oxygen atom in the Si–O–Si bridge upon switching of adjacent bridging bonds. The activation energy e h = Pmaxνh and the activation volume νh = πd2Δrmax of the atomic excitation are introduced. The activation energy e h is determined by the work done against the forces of the internal pressure Pmax. The formation of an excited kinetic unit in polymers and glasses is a small-scale low-energy process (e h = 10–20 kJ/mol, νh = 5–70 A3). The total activation volume of the system Vf = νhNh is termed the fluctuation volume, and the model under consideration is referred to as the fluctuation volume model (or the model of excited atoms). The viscosity equation and other relationships of the hole theory are interpreted in the framework of the proposed model. This model is also applied to analyze the plasticity of amorphous polymers and glasses. A relationship between the glass transition condition and the Lindemann melting criterion is established.

Study of tack properties of uncrosslinked natural rubber

The purpose of this study was to better understand the effect of non-rubber substances (mainly proteins and lipids) on adhesion (against glasses) and self-adhesion tack properties of uncrosslinked natural rubber (NR). Various types of NR, with or without non-rubber constituents, were prepared. Synthetic polyisoprene rubber was also used as a reference material. All the rubbers were first characterized by many techniques (FT-IR, DSC, GPC, etc.). Two experimental tests were specially utilized to measure the level of adhesion and self-adhesion: (i) at very short contact times (from a few milliseconds up to 0.1 s) the impact of a pendulum and (ii) for longer contact times (from 0.1 s to a few h) the contact of a probe using a tensile testing machine. The tack energy increased with contact time for all the rubbers studied. Natural rubber which did not contain proteins and lipids exhibited the highest adhesion and self-adhesion tack abilities. In contrast, whole natural rubber, containing both proteins and lipids, showed the lowest tack property. In each case, self-adhesion levels are higher than those of adhesion, presumably due to interdiffusion of macromolecular chains or chain segments at the interface.

Comparison and Characterization of Polyester Fiber and Microfiber Structure by X-ray Diffractometry and Viscoelasticimetry

The authors have studied three polyethylene terephthalate filaments from the same manufacturer. The results of the dyeing process depend on the filaments' characteristics. Dyeing modifies the macromolecular organization according to the manufacturing process. To understand the dyeing influence, each filament is subjected to a heat treatment that reproduces the effect of dyeing. The organizational molecular modifications are determined by x-ray diffraction and viscoelasticimeter measurements. The study shows that drawing and shearing align macromolecules, affecting the crystallinity. The crystallinity of a trilobal filament and of a microfilament are almost identical whatever the heat treatment. The less significant drawing of a circular filament provides a more amorphous and more sensitive filaments for heat treatment. Super-drawing induces the existence of macromolecular segments of a great mobility. Moreover, a heterogeneity of the organization is detected at the glass transition point.

Polyester Fiber and Microfiber Structure by X-Rays and Viscoelasticimetry

We have studied three polyethylene terephthalate filaments from the same manufac turer. The results of the dyeing process depend on the filament characteristics. Dyeing modifies the macromolecular organization according to the manufacturing process. To understand the dyeing influence, each filament undergoes heat treatments that reproduce the effect of dyeing. Organizational molecular modifications are determined by x-ray diffraction measurements and by a viscoelasticimeter. The study shows that drawing and shearing align macromolecules that act on the crystallinity. Thus, the crystallinity of a trilobal filament and a microfilament are almost identical, whatever the heat treatment. The less significant drawing of a circular filament provides more amorphous and more sensitive filaments for heat treatment. Super-drawing induces the existence of macromo lecular segments of great mobility. Moreover, organizational heterogeneity is detected at the time of the glass transition.