Mechanical response of three semi crystalline polymers under different stress states: Experimental investigation and modelling

The mechanical responses of high‐density polyethylene (HDPE), polypropylene (PP) and polyamide 6 (PA 6) were experimentally investigated for a wide range of stress states and strain rates. This was accomplished by testing numerous specimens with different geometries. The uniaxial compression of cylindrical unnotched specimens and the uniaxial tensile behaviour of dumbbell specimens at different strain rates, was determined. A series of biaxial loading tests (combined shear and tension/compression, pure shear, pure tension/compression) using a designed Arcan testing apparatus were also performed. Flat and cylindrical notched specimens with different curvature radii were additionally tested in order to explore a wider range of stress states. The Drucker‐Prager yield criterion was calibrated with a set of experimental data, for which analytical formulae for stresses are available, and then applied to predict the deformation behaviour under different stress states, prior to strain localization. The results of the numerical simulations show that the Drucker‐Prager model can capture the initial elastic range and the post‐elastic response very satisfactorily. For triaxial and biaxial stress states there is a good agreement, however some load‐displacement responses are only satisfactorily described. Deviations observed in the predicted and experimental results are very likely attributed to the third invariant stress tensor, which was not explored in the model calibration. The evolution of stress triaxiality and Lode angle parameters with equivalent plastic strain were extracted and analysed for several specimens. The results show a plastic yielding behaviour sensitive to the stress state, which can be attributed to different combinations of stress triaxialities and Lode angle parameters.     

COMPARISON OF POLYAMIDE 66/MONTMORILLONITE NANOCOMPOSITES PREPARED FROM POLYAMIDE 6 AND POLYAMIDE 66 BASED MASTER-BATCHES

Two master-batches,polyamide 66 (PA66)/organo-montmorillonite (OMMT) and polyamide 6 (PA6)/OMMT, prepared by melt compounding with methyl methacrylate (MMA) as co-intercalation agent,have been used to prepare nearly exfoliated PA661montmorillonite (MMT) nanocomposites.The resulting nanocomposites are compared in view of their morphology and properties.Nano-scale dispersion of OMMT is realized in both types of nanocomposites,as revealed by XRD,TEM and Molau tests.PA66/MMT nanocomposites having superior me...     

Yield Stress Measurement of Dense Pastes with Pipe Transport and Vane

Yield stress is a key rheological parameter of dense paste. Considering practical utility and to estimate the possible slipping flow, yield stress measurements were carried out using the curve extrapolation method and vane method with rheometer in both controlled shear stress (CSS) and controlled shear rate (CSR) model. All measured yield stresses show to increase exponentially with concentration in different scale. The vane method yield stresses are both higher than the extrapolation curve yield stress. For the coal slurry used in this paper, the extrapolation curve yield stress is lower by 17–30% than the dynamic yield stress that obtained under test model CSR. It indicates that wall slip exists in pipeline transportation; meanwhile wall slip can reduce transportation resistance of dense paste to some extent.     

半芳香尼龙6T/66的合成和非等温结晶动力学的研究

采用成盐、预聚合、固相聚合三步法制备高分子量的PA6T/66,用差示扫描量热法(DSC)研究了PA6T/66的非等温结晶动力学,结果表明:结晶温度随着降温速率的增大而降低;半结晶期T1/2随降温速率Ф的增大呈指数下降,表明结晶速率随降温速率的增大而提高;由用R-T法可以得到在不同结晶度下lgΦ对lgT有较好的线性关系。用Kissinger方法计算得到PA6T/66(55/45)非等温结晶活化能分别为ΔE=-61.51kJ/mol。     

Miscibility of Semi-flexible Thermotropic Liquid Crystalline Copolyesteramide with Polyamide 66

IntroductionIn sl'tu polymer composites containing liquid crystalline polymers(LCPs) have attractedconsiderable attention in the past'decades['--'j. But the development of in sl'tu composites is restricted by two factors. First, the melting temperatures of thermotropic liquid crystallinepolymers (TLCPs) are generally higher than those of the commodity engineering resins. Athigh processing temperatures, these resins tend to become unstable, thereby, causing seriousproblems during fiber spinn…     

Polyamide‐6/natural clay mineral nanocomposites prepared by solid‐state shear milling using pan‐mill equipment

The polyamide‐6 (PA6)/natural clay mineral nanocomposites were successfully prepared by solid‐state shear milling method without any treatment of clay mineral and additives. PA6/clay mixture was pan‐milled to produce PA6/clay compounding powder, using pan‐mill equipment. The obtained powder as master batch was diluted with neat PA6 to prepare composites by a twin‐screw extruder. The clay silicate layers were found to be partially exfoliated and dispersed homogeneously at nanometer level in PA6 matrix. The rheological measurements and mechanical properties of nanocomposites were characterized. The shear viscosities of nanocomposites were higher than that of pure PA6, and tensile strength and tensile modulus increased, but Izod impact strength decreased, with increasing concentration of clay. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 249–255, 2006     

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.     

Quasi-static failure behaviour of PMMA under combined shear–compression loading

Quasi-static shear–compression tests were conducted on polymethyl methacrylate (PMMA) polymer specimens using a universal materials testing machine to investigate their failure behaviour under quasi-static multi-axial loading. Instead of using confining pressure, cylindrical specimens with bevelled ends of different angles (5°, 10°, 15°, 20°, 25° and 30°) were used to generate different shear stresses. In addition, a cylindrical specimen with no bevelled ends and a hat specimen of PMMA were applied in the quasi-static shear–compression tests to determine the compression and shear strengths of PMMA, respectively. Experimental results show that the failure force of PMMA decreased as the tilt angle of the specimen increased. Furthermore, the failure locus of the material can be predicted using a macroscopic failure criterion with an elliptical shape. The deformation modes of each type of PMMA specimen under quasi-static loading were determined.     

One-step water-assisted melt-compounding of polyamide 6/pristine clay nanocomposites: An efficient way to prevent matrix degradation

Polyamide 6 (PA6)/clay nanocomposites, based on organo-modified and pristine (i.e. purified but non-modified) montmorillonite, were prepared using a water-assisted extrusion process based on the injection of water during extrusion. The formation of a single PA6/water phase during extrusion (shown by High Pressure Differential Scanning Calorimetry (HPDSC)) improves the clay dispersion, decreases the PA6 melting temperature by 66 °C (so-called cryoscopic effect), and thus prevents the polymer matrix degradation during processing. This process enables the compounding of pristine clay-based nanocomposites whose dispersion state, thermal and mechanical performances are close to what is generally reported for organo-modified montmorillonite-based nanocomposites. Advantage was taken of water-assisted extrusion to optimize the clay dispersion by increasing shear rate and of the cryoscopic effect to limit the degradation by decreasing the processing temperature. Using these conditions PA6/pristine clay nanocomposites properties are similar to those of more conventional PA6/organomodified clay nanocomposites.     

Polyamide 6 with a flame retardant encapsulated by polyamide 66: Flame retardation, thermo-decomposition and the potential mechanism

A novel encapsulated flame retardant containing phosphorus-nitrogen(MSMM-Al-P) was prepared by encapsulating with polyamide 66(PA66-MSMM-Al-P) for the flame retardation of polyamide 6(PA6).The structure and thermal properties of PA66-MSMM-Al-P were characterized by Fourier-transform infrared spectroscopy,X-ray photoelectron spectroscopy and thermogravimetric analysis.The flammability of PA6 containing flame retardants(MSMM-Al -P and PA66-MSMM-Al-P) was investigated by the limiting oxygen index test,vertical burning test and cone calorimeter. The flame retardancy and cone calorimetric analyses suggested a synergistic effect between PA66 and MSMM-Al-P in the flame-retardant PA6.Thermal stability of the flame-retardant PA6 was also investigated.     

X‐ray absorption,particle orientation,and rheological behavior of talc–calcite mixed‐particle compounds in a polystyrene matrix

This article presents experimental studies of (a) X‐ray absorption, (b) particle orientation, and (c) the shear viscosity of ternary talc–calcite–polystyrene compounds. A quantitative investigation of X‐ray absorption using a wide‐angle X‐ray diffraction (WAXD) intensity method for binary mixture (PS/talc, PS/calcite) systems and ternary mixtures (PS/talc/calcite) systems is reported. The Alexander–Klug equation was used to interpret the data. X‐ray diffraction pole figures indicate that talc particles orient in shear flows perpendicular to the direction of shear with their surfaces parallel to die/mold walls. There was a general tendency in mixed particle systems for the talc particles to decrease in orientation with increasing calcite content. The shear viscosity of the compounds was measured and found to increase with increasing particle loading and vary with particle composition. The talc, calcite, and talc/calcite‐filled thermoplastic melts at higher loadings were found by creep measurements to exhibit yield values, i.e., stresses below which there is no flow. We found a viscosity–shear stress plateau at low shear stress. The true yield values are much lower than yield values measured by extrapolation of higher shear stress data. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1787–1802, 1999     

Effect of maleic anhydride-grafted ethylene-propylene rubber on the mechanical, rheological and morphological properties of organoclay reinforced polyamide 6/polypropylene nanocomposites

Polyamide 6/polypropylene (PA6/PP = 70/30 parts) blends containing 4 phr (parts per hundred resin) of organophilic modified montmorillonite (organoclay) were compatibilized with maleic anhydride-grafted ethylene-propylene rubber (EPRgMA). The blends were melt compounded in twin screw extruder followed by injection molding. The mechanical properties of PA6/PP nanocomposites were studied by tensile and flexural tests. The microstructure of the nanocomposite were assessed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The dynamic mechanical properties of the PA6/PP blend-based nanocomposites were analyzed by using a dynamic mechanical thermal analyzer (DMTA). The rheological properties were conducted from plate/plate rheometry via dynamic frequency sweep scans. The melt viscosity in a high shear rate region was performed by using a capillary rheometer. The strength and stiffness of the PA6/PP-based nanocomposites were improved significantly with the incorporation of EPRgMA. Adding EPRgMA to the PA6/PP blends resulted in a finer dispersion of the PP phase. TEM and XRD results revealed that the organoclay was dispersed more homogeneously in the presence of EPRgMA, however, mostly in the PA6 phase of the blends. DMTA results showed that EPRgMA worked as an effective compatibilizer. The storage (G′) and loss moduli (G″) assessed by plate/plate rheometry of PA6/PP blends increased with the incorporation of EPRgMA and organoclay. Furthermore, the apparent shear viscosity of the PA6/PP blend increased significantly for the EPRgMA compatibilized PA6/PP/organoclay nanocomposite. This was traced to the formation of an interphase between PA6 and PP (via PA6-g-EPR) and effective intercalation/exfoliation of the organoclay.     

PET／PA66／液晶共聚酯酰胺共混体系的流变性能

采用ＳＥＭ１、热偏光显微研究了聚对苯二甲乙二酯（ＰＥＴ）／聚酰胺６６（ＰＡ６６）／热致液晶共聚酯酰胺（ＬＣ３０）三元共混物的形态结构;利用Ｉｎｓｔｒｏｎ３２１１型毛细管流变仪研究了共混物的流变性能,结果表明：ＰＥＴ／ＰＡ６６／ＬＣ３０共混物为一热力学不相容的多相聚合物体系,ＬＣ３０的加入提高了ＰＥＴ／ＰＡ６６的相容性,有效地改善了ＰＥＴ／ＰＡ６６共混物的流变性能,ＰＥＴ／ＰＡ６６／ＬＣ３０三元共混     

Quick analysis of composition of semi-aromatic copolyamide via 13C NMR study

Standard high resolution ¹³C NMR spectra of PA10T, PA6T, PA106, and PA66 were obtained by a nonacidic solvent mixture of HFIP and CDCl₃. Several chemical shifts were found extremely sensitive to the polyamide type. According to the standard spectra, semi-aromatic copolyamides comprising PA10T, PA6T, PA106, and PA66 units could be distinguished. The ratio of each polyamide component in the copolyamide was determined through the integration of the methylene carbon peak associated with the amine group. ¹³C NMR analysis results were consistent with the theoretical values and copolyamide hydrolysis test results, making ¹³C NMR analysis quite reliable on the quick composition analysis of semi-aromatic copolyamides. Based on this technique, several commercial semi-aromatic copolyamides were further examined and their compositions were easily determined.     

Cellulose-polyamide 66 blends. I. Processing and characterization

Each homopolymer, cellulose and polyamide 66 (PA66), was separately dissolved in a mixture of N-methyl morpholine N-oxide and phenol (80/20 w/w). Then, the two solutions were mixed together. This step leads to the crystallization of PA66 in small aggregates (about 1 μ) regularly dispersed in the cellulose solution. It appeared that this morphology remains independent of further processing such as spinning or casting. Finally, fibers or films were precipitated in methanol. The entire preparation technique used here results mainly in two-phase systems in which PA66 domains are embedded in an amorphous cellulose matrix. The specimens obtained were at first characterized by differential scanning calorimetry, scanning electron microscopy, and wide angle x-ray scattering. © 1994 John Wiley & Sons, Inc.     

Thermogravimetric studies on Polyamide-6,6 modified by electron beam irradiation and by nanofillers

This paper reports the results of thermogravimetric studies on: (a) Polyamide-6,6 (abbreviated henceforth as PA66) specimens which were modified by electron beam radiation in air, (b) organic-inorganic hybrid nanocomposite films of PA66/silica prepared by the sol-gel technique and (c) unmodified multi-walled carbon nanotube (abbreviated henceforth as MWCNT) reinforced PA66 films. The activation energies were determined using the Kissinger and the Flynn-Wall-Ozawa methods, which do not require knowledge of the reaction mechanism. The results showed that PA66 specimens which received an irradiation dose of 200 kGy in air had a higher thermal stability than both the neat PA66 and PA66 specimens which received a radiation dose of 500 kGy in air. The PA66/silica hybrid nanocomposites up to a silica loading of 1.5 wt% also showed higher thermal stability over neat PA66 films. At MWCNT loadings of 0.5-1.0 wt% the composite films exhibited higher activation energies than the neat PA66 film but at higher MWCNT loading the activation energy was lower than that obtained for the neat PA66 film.     

Thermal and crystallization studies of nano-hydroxyapatite reinforced polyamide 66 biocomposites

The thermal and crystalline behaviour of nano-hydroxyapatite (n-HA) reinforced polyamide 66 (PA66) biocomposites was studied by thermogravimetry (TG) and differential scanning calorimetry (DSC). The thermal properties of PA66 and n-HA/PA66 composites were analysed by TG. The effect of hydroxyapatite on the melting and crystallization of PA66 was evaluated by DSC. DSC measurements exhibited an increase in the crystallization temperature, however, decrease in crystallinity with the addition of n-HA to the PA66 matrix, which was attributed to the hydrogen bonds between the n-HA surface and polyamide 66 molecules. With increase of n-HA content, the melting peak of the PA66 component shifted to higher temperature, suggesting constrained melting. The addition of n-HA to PA66 played the role of nucleating agent and enhanced the crystallization rate. Non-isothermal parameter a measured by Liu method varies from 1.13 to 1.18, from 1.02 to 1.07, and from 1.18 to 1.21 for PA66, 30 wt% n-HA/PA66 and 40 wt% n-HA/PA66, respectively, and the values of K_(T) systematically increase with rise in relative degree of crystallinity.     

基于纳米羟基磷灰石溶胶的nHA/PA66复合粉体制备与表征

本文开发了一种新的制备纳米羟基磷灰石(nHA)/聚酰胺66(PA66)复合材料的方法。先用明胶包覆nHA棒状颗粒,再将其制备成以N,N-二甲基乙酰胺和甘油的混合液为溶剂的稳定溶胶。当nHA溶胶与PA66溶液混合时,相同的酰胺基团保证了二者之间良好的共混相容性,成功制备了nHA/PA66复合材料。X射线衍射(XRD)、傅立叶红外光谱分析(FTIR)、透射电镜(TEM)、扫描电镜-能谱分析(SEM-EDS)以及差热分析(DTA)和热重分析(TG)等表征了产物的形貌、结构及成分分布。结果表明：明胶对nHA颗粒具有显著的化学包覆作用,使nHA溶胶与PA66溶液得以均匀混合,均匀分布在PA66基体中,二者以氢键结合为一体。     

The addition of clay on the mechanical properties of surface‐treated CF‐filled PA66 composites

Polyamide 66 (PA66) composites filled with clay and carbon fiber (CF) were prepared by twin‐screw extruder in order to study the influence of nanoparticle reinforcing effect on the mechanical behavior of the PA66 composites (CF/PA66). The mechanical property tests of the composites with and without clay were performed, and the fracture surface morphology was analyzed. The results show that the fracture surface area of the clay‐filled CF/PA66 composite was far smoother than that of the CF/PA66 composite, and there formed a tense interface on the CF surface after the addition of clay. The tensile and flexural strength of CF/PA66 composites with clay was improved. The impact strength decreased because of the high interfacial adhesion. In conclusion, the addition of clay favored the improvement of the higher interface strength and so had good effect on improving the tensile and flexural properties of the composites. Copyright © 2017 John Wiley & Sons, Ltd.