Composites of polyamide 6 and silicate nanotubes of the mineral halloysite: Influence of molecular weight on thermal, mechanical and rheological properties

In this work, the potential of silicate nanotubes of the naturally occurring mineral halloysite as filler for polyamide 6 (PA 6) nanocomposites is evaluated. Several PA 6/halloysite composites with 0 wt% to 30 wt% filler loading using two different grades of PA 6 were prepared. In order to elucidate the influence of molecular weight on the properties of the nanocomposites, mechanical resp. rheological experiments (i) below the glass transition temperature T_g of PA 6, (ii) between T_g and the melting temperature T_m of PA 6 and (iii) above T_m were performed. Our investigations reveal that the addition of halloysite nanotubes favours the formation of the γ-modification for the low molar mass PA 6. Furthermore, the storage modulus, the tensile modulus and the yield stress of the composites increase with concentration of halloysite, an effect which is strongly pronounced at very low filler fractions for the low molar mass PA 6 composites. The increase of the storage modulus which was measured in dynamic-mechanical experiments is mostly dominant in the temperature interval from 55 °C to 100 °C, i.e. above the glass transition temperature of PA 6. Rheological investigations showed that the shear viscosity is only moderately increased by the addition of a low fraction of halloysite to PA 6, and nanocomposites with 30 wt% halloysite can be still processed. In summary, halloysite nanotubes are promising and inexpensive candidates for increasing the stiffness of PA 6 while maintaining very good flow properties.     

Effect of molecular weight distribution on the rheological and mechanical properties of polypropylene

The effect of molecular weight distribution on the Theological and mechanical properties of a series of polypropylenes is evaluated. The polypropylenes tested were produced by controlled chemical degradation in a single-screw plasticating extruder. Measured properties include shear, extensional and intrinsic viscosity, melt flow index, extrudate swell, melting and crystallization temperatures, impact strength, flexural modulus, and tensile stress.     

Influence of organophilic montmorillonite and polypropylene on the rheological behaviors and mechanical properties of ultrahigh molecular weight polyethylene

The effects of organophilic montmorillonite (OM)/poly(ethylene glycol) (PEG) hybrids and polypropylene (PP) on the phase morphology, rheological behaviors, and mechanical properties of ultrahigh molecular weight polyethylene (UHMWPE) were investigated. The presence of the OM/PEG hybrids and PP in UHMWPE was found that it was able to lead to a significant reduction of melt viscosity and enhancement in tensile strength, and elongation at break of UHMWPE. A quantitative analysis indicated a larger affinity of the OM to the PEG than to PP or UHMWPE in the composites, suggesting that OM was intercalated by PEG. This was proposed to be responsible for the reduction of viscosity. Polarizing optical microscopy analysis, on the other hand, indicated that the dispersed OM, which acted as a nucleating agent, lowered the spherulite dimension and increased the spherulite number, resulting in high tensile strength and elongation at break. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Fiber reinforced polypropylene: Influence of iPP molecular weight on morphology,crystallization, and thermal and mechanical properties

The influence of molecular weight and its distribution on the nucleation density, crystallization, thermal and mechanical behavior of isotactic polypropylene based composites has been investigated. The composites were prepared by compression molding. The ability of carbon and Kevlar fibers to nucleate the polypropylene has been studied during isothermal and nonisothermal crystallization, by optical microscopy and differential scanning calorimetry (DSC), as function of crystallization temperature T_c and iPP molecular weight. Two extreme crystallization conditions were tested: quenching and slow crystallization to obtain crystals and amorphous phases of different structure. The ability of fibers to enhance mechanical properties in polypropylene based composites was examined by tensile tests at room temperature. It was found that nucleation density, crystallization parameters, and the results of tensile tests strongly depend on the molecular weight M w of iPP, molecular weight distribution, and thermal history of polypropylene. The numerical values of the nucleation density have been found to strongly depend on the nature of fiber. In fact, Kevlar fiber has shown a better nucleating ability than carbon fiber. The results of tensile tests have been related to the sample morphology. The analysis of fractured specimens also provided useful information about fiber-matrix adhesion.     

Influence of the molecular weight on the thermal and mechanical properties of ethylene/norbornene copolymers

A series of ethylene‐norbornene copolymers were synthesized using Me₂Si(Me₄Cp)(NtBu)TiCl₂ as the metallocene catalyst and methylaluminoxane (MAO) as the cocatalyst, with the same molecular characteristics except the molecular weight, to evaluate its influence on the determination of the glass transition temperature (T_g). The polymers were characterized using wide‐angle X‐ray scattering, differential scanning calorimetry, microhardness measurements, and dynamic mechanical thermal analysis. The value of the T_g, for the same norbornene content and determined from the last three mentioned methods, increases significantly up to a limit of M_n about 6–10 × 10⁴ (g/mol). Above this value, T_g remains practically constant. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3358–3363, 2003     

Influence of molecular weight on some rheological properties of acrylic solutions during newtonian flow

The effect of molecular weight in a narrow range on some rheological properties of acrylic solutions during Newtonian flow at different temperatures and concentrations was investigated. The results showed that the change in viscosity with temperature and concentration was dependent on the molecular weight. It was found that the molecular weight in a closer range influenced the activation entropy and the free energy of activation during Newtonian flow.     

Influence of processing parameters and molecular weight on the mechanical properties of PVC

The role of a variety of processing parameters in determining the mechanical properties of solid PVC has been examined. Annealing pretreatment has been shown to increase both the yield stress and the modulus. It was found that the density of the material similarly increased as the annealing progressed, and when the density reached a limiting value, the yield stress and modulus also reached a limiting value. The molecular weight of the resin, as measured by its intrinsic viscosity, also affected the various mechanical properties measured. However, the yield stress increased while the modulus decreased as the molecular weight increased. This unusual behavior was thought to be a secondary effect. Finally, the addition of increasing amounts of stabilizer to the PVC resin resulted in an increase in modulus and a decrease in yield stress. This was consistent with a model for plastic deformation in which the stabilizer acted as small hard particles. The activation strain volume did not change with different concentrations of stabilizer, further supporting a model for a two-phase structure.     

Effects of maleic anhydride grafted polyethylene on rheological,thermal, and mechanical properties of ultra high molecular weight polyethylene/poly(ethylene glycol) blends

Ultra‐high molecular weight polyethylene (UHMWPE) has gained considerable fame due to its excellent wear and mechanical properties, though the inferior processability has restricted its further extensive applications. In this study, a combination of UHMWPE and poly(ethylene glycol) (PEG) was considered based on the recent reports, and aiming to further exploit the potential of PEG that acts as processing aid, and also to obtain greater enhanced processability along with other properties, the effects of incorporating maleic anhydride grafted polyethylene (MAPE) was thoroughly investigated. Rheological tests revealed a further significant reduction in melt viscosity of UHMWPE/PEG blends after MAPE introduced, showing a potential of better processability, while the flexural strength and toughness of UHMWPE blends experienced a satisfying increase without any obvious compromises in other mechanical properties. A slight improvement of thermal stability in UHMWPE ternary blends along with an increase of vicat softening temperature were characterized by thermal tests, while the crystallinity of UHMWPE was diminished after the introduction of MAPE. Morphology analysis indicated that better dispersion and decreased size of PEG particles were achieved in UHMWPE matrix when MAPE was incorporated, which confirmed the improved interfacial interactions and other reinforcements obtained in UHMWPE/PEG/MAPE blends. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42701.     

Influence of molecular parameters on thermal,mechanical, and dynamic mechanical properties of hydrogenated nitrile rubber and its nanocomposites

The present work derives a relationship between structure and properties of hydrogenated nitrile rubber (HNBR) in the presence as well as absence of nanofillers. Four different grades of HNBR were selected to examine the influence of polarity, unsaturation, and molecular weight on thermal, mechanical, and dynamic mechanical properties of the elastomers and particularly their nanocomposites. An increase in thermal stability, tensile strength, modulus at 100% elongation as well as storage modulus of the unfilled rubber was observed with increase in polarity (acrylonitrile content). Different nanofillers, such as montmorillonite, sepiolite, and nanosilica were used to improve the above properties of the unfilled rubber. Interestingly, a reverse trend of thermal properties was observed for the nanocomposites with acrylonitrile variation, although mechanical and dynamic mechanical properties exhibited similar trend to those of the unfilled rubber. These properties, however, gradually deteriorated as the level of unsaturation on the polymer backbone was increased. On addition of the nanofillers, it was found that the improvement in thermal and mechanical properties was higher for the elastomer having 5.5% diene content. The results were explained by X‐ray Diffraction, Atomic Force Microscopy, Energy Dispersive X‐ray mapping, and swelling studies. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Influence of molecular weight on the thermal and mechanical properties of polyurethane elastomers based on 4,4′-diisocyanato dicyclohexylmethane

Two series of segmented polyurethane elastomers based on 4,4′-diisocyanato dicyclohexylmethane were investigated with respect to their thermal properties and deformation behavior. We used a crystallizable soft segment, 1,4-poly(tetramethylene glycol), for one series and a noncrystallizable soft segment, 1,2-poly(propylene glycol), for the other. Both systems exhibited mechanical self-reinforcement that depended strongly on the deformation rate. We propose a mechanism for the observed stress/strain behavior in terms of two competing processes: (1) the buildup of orientation caused by deformation and (2) the loss of orientation caused by plastic slippage and segmental relaxation during deformation. The kinetics of these processes depend stronly on the deformation rate and overall molecular weight.     

Effects of molecular weight on the dynamic mechanical and rheological properties of anionically polymerized polyamide 6 containing nanofiber

Anionic ring‐opening polymerization of ε‐caprolactam leads to the formation of polyamide 6 (PA6). This reaction takes place at a significantly faster rate and gives a narrower molecular‐weight distribution than those obtained with other techniques. Because of this advantage, anionic polymerization of PA6 during melting was investigated in this work. In an internal mixer, PA6 was prepared via the melt polymerization of ε‐caprolactam as monomer with sodium caprolactam as a catalyst and hexamethylene diisocyanate as an activator. The effects of various concentrations of catalyst and activator on the rate of reaction and the amount of residual monomer were determined. Also, the physical and mechanical properties of PA6 prepared in this way and commercial PA6 prepared via hydrolytic processing were determined by differential scanning calorimetry and dynamic mechanical thermal analysis, as well as tensile, impact, and rheological tests. The experimental results showed that the composition which included 3% of catalyst and 3% of activator gave better properties than the other formulations. These conditions led to the lowest residual monomer content and better mechanical properties, as well. Another novel aspect of this investigation was nanofiber formation during the melt polymerization. The nanofibers had lower molecular weights than the matrix and thus created a special crystal structure different from that of the matrix. Mechanical property measurements showed that PA6 prepared by using this technique and the aforementioned formulation was similar to the commercial PA6. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers     

Effect of molecular weight of phenalkamines on the curing,mechanical, thermal and anticorrosive properties of epoxy based coatings

The present investigation deals with the study of effect of molecular weight and structures of phenalkamine curing agents on the curing, mechanical, thermal and anticorrosive properties of epoxy based coatings. The phenalkamines were prepared by varying the composition of formaldehyde and diamine in the formulation. The structural characterization confirmed successful preparation of high molecular weight phenalkamines. These were then used as curing agents for air drying and thermally curable epoxy coatings. The effect of these phenalkamines on curing properties of epoxy resin as well as mechanical, chemical, thermal and dynamic thermo-mechanical properties of the resultant coatings was studied and compared with commercial phenalkamine. The anticorrosive properties of the coatings were evaluated by salt spray test and electrochemical impedance spectroscopy. The study revealed that high molecular weight phenalkamines resulted in faster surface drying due to rapid molecular weight build-up. The anticorrosive performance also improved as indicated by higher modulus and electrochemical potential values.     

Effect of solvent,concentration, and molecular weight on the rheological properties of polymer solutions

The zero-shear viscosity η⁰ of polychloroprene samples of different molecular weights over a wide range of concentration in good and poor solvents has been studied. Butanone and cyclohexane were used as θ solvents and benzene at two different temperatures (25 and 45.5°C) was used as two good solvents. The zero shear specific viscosity η in θ solvents, at the high concentration region is found to be higher compared to the values obtained in good solvents. whereas in a moderately concentrated region the values are just opposite in θ and good solvents. The high values of specific viscosity in poor solvent at the concentrated region have been explained as due to the fact that the efficiency of entanglements is much bigger in θ solvent than in good solvent. There are indications from our data that, at the crossover point concentration, the onset of entanglements begins, and from this concentration the entanglement begins to play a role in the viscosity. The superposition of viscosity data for each solvent was carried out by shifting vertically the curve along log η⁰ axis at constant concentration by a factor (M/M⁰)^3.4, where M⁰ is the molecular weight of the reference sample. The shift factor was found to be exactly proportional to M^3.4 in the range of higher concentration (beyond the crossover point concentration) and approximately to M in the lower concentration range (below the crossover point concentration). This showed that the relation η⁰ ∝ M^3.4 was obeyed by the present data. To correlate the viscosity data obtained at good and θ solvents, the method as given by Graessley has been employed, which has taken into account the contraction of dimensions of chains with concentration in good solvents. It has been observed that, though this approximate correction for variation of chain dimensions on correlating variable, C[η], has moved the correlations for θ and good solvents closer to a common curve, complete superposition of data has not been effected by this correction. On the other hand, the correlation of the data by the method given by Dreval and co-workers showed the plot of log{η/(C[η])} vs. C[η] produced a single curve for solutions of polychloroprene samples in two different θ solvents (butanone and cyclohexane) over the entire concentration range. But in the case of good solvents (benzene at 25°C and benzene at 45.5°C) the similar plots yielded, instead of one, two curves. However, the normalization of the correlating variable, C[η], by the Martin constant K_M, which is related to the flexibility of macromolecular chain and polymer-solvent interaction, reduced all data of the polymer samples to a common curve. This zero-shear viscosity master curve is valid for the entire range of concentration independent of molecular weight and the nature of solvents.     

Main‐chain benzoxazine oligomers: Effects of molecular weight on the thermal,mechanical, and viscoelastic properties

With the intent to study materials processing properties during the curing process, oligomeric benzoxazines of different molecular weight and distribution were obtained from 4‐tert‐butylphenol, bisphenol A, 4,4′‐diaminodiphenylmethane and paraformaldehyde by varying the amounts of phenolic compounds. Average molecular weight and distribution of prepared mixtures of polybenzoxazine precursors were determined by gel permeation chromatography analysis. By knowing the molecular weight distribution of prepared mixtures of polybenzoxazine precursors its effect on thermal, mechanical, and viscoelastic properties of the resin during processing and polymerization could be investigated. Mixtures of polybenzoxazine precursors of higher average molecular weight and broader molecular weight distribution displayed faster curing, lower curing conversions, and higher crosslinking densities of cured resins leading to polybenzoxazines with improved properties. This investigation was oriented towards the material processing aspects with the focus on the effect of molecular weights and viscoelastic properties of starting materials on the proceeding of the curing, including changes in material properties, and sample molding. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46659.     

Influence of organo-montomorillonite on mechanical and rheological properties of polyamide nanocomposites

The effect of organically modified montmorillonite (OMMT) on polyamide nanocomposites was studied. OMMT/polyamide nanocomposites were prepared through direct melt compounding on a conventional twin screw extruder. With increasing the loading of OMMT, the Young modulus, elongation at break and tensile strength increased. 1 mass% loading of OMMT/polyamide resulted in 11% increase of the elongation at break compared to virgin polymer, while 4% loading showed 13%. Rheological data like torque, fusion time, viscosity and shear rate were also recorded on Brabender Plasticorder and were correlated with M = CS^a and τ = K(γ)ⁿ. The value n < 1 indicated pseudo-plastic nature of the polyamide/OMMT. The torque decreased with increased loading due to soft nature of OMMT, which acts as a lubricating agent. This improvement in mechanical properties with increase in amount of OMMT loading was also indicated by the reduction in shear viscosity and torque.     

Flame retardancy,thermal, rheological,and mechanical properties of polycarbonate/polysilsesquioxane system

The polymethylphenylsilsesquioxane (PMPSQ) microspheres were used as an additive for the injection‐molding of polycarbonate (PC) in order to obtain a flame retardant polymer and to damage the other properties of PC as low as possible. The results showed that PMPSQ microspheres were a kind of effective flame retardant by the LOI test and the flame retardancy of PC increased with the increase of PMPSQ content. Thermogravimetric analysis suggested that the PMPSQ could induce crosslinking reactions and accelerate the thermal degradation of PC, sequentially promote the formation of the residue char during degradation. Differential scanning calorimetry measurement showed that the glass transition temperature of PC/PMPSQ system was decreased with the increase of PMPSQ content, which maybe caused by the enlarged free volume of PC‐rich phase. The rheological behaviors including dynamic and steady modes, combined with the analysis of scanning electron microscopy photographs, exhibited that the dispersion and compatibility of PMPSQ in the PC matrix decreased the viscosity of the systems and the addition of PMPSQ microspheres improved the processability of PC, but still there exist aggregation of PMPSQ microspheres in PC matrix, which gave a higher impact strength but a lower flexural modulus and elongation at break than pure PC. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of morphology on rheological and mechanical properties of SEBS-toughened,glass-bead-filled isotactic polypropene

The influence of morphology of glass-bead-filled isotactic polypropene containing 0–20 vol% thermoplastic elastomers (TPE) on mechanical and rheological properties was investigated. Polystyrene-block-poly(ethene-co-but-1-ene)-block-polystyrene(SEBS) and the corresponding block copolymer grafted with maleic anhydrid (SEBS-g-MA) were used as thermoplastic elastomers, realizing, in the first case, a three-phase morphology with separately dispersed glass beads and SEBS particles. In the second case, SEBS-g-MA forms an elastomeric interlayer between glass beads and polypropene matrix, comprising core–shell particles. Young's modulus and tensile yield stress of the hybrid composites decrease with an increase in TPE volume fraction due to low stiffness and strength of TPE. In comparison with the three-phase morphology of hybrid composites with SEBS, SEBS-g-MA interlayers effect a reduced stiffness of the hybrid composites but improve interfacial adhesion and, thus, tensile yield stress. Rheological storage and loss moduli increase with an increase in glass bead and TPE volume fraction. Due to improved interfacial adhesion, melt elasticity and viscosity are enhanced by the SEBS-g-MA interlayer when compared with separately dispersed SEBS. Consequently, the reduced stiffening effect of the glass beads due to SEBS-g-MA interlayer decreases mechanical elasticity, whereas improved interfacial adhesion, also promoted by the SEBS-g-MA interlayer, enhances tensile yield stress and melt elasticity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2499–2506, 1998