Effect of ultrasonic oscillations on weld line strength of PS,PMMA, and their blends

The effect of ultrasonic oscillations on the weld line strength of amorphous polystyrene (PS), polymethyl methacrylate (PMMA), and PS/PMMA (20/80, 50/50, 80/20) blends at various temperatures was investigated. By facilitating the molecular diffusion across the weld line, the introduction of ultrasonic oscillations could evidently improve the weld line strength of PS, PMMA, and their blends. The different effects on the weld line strength of PS/PMMA (20/80, 50/50, 80/20) blends were investigated. The ultrasonic oscillations could greatly increase the weld line strength of PS/PMMA (80/20) by ～ 70%, but was less efficient to PS/PMMA (50/50, 20/80) blends, due to the great difference of weld line morphologies of these blends. The dispersed phase of PS/PMMA (80/20) in the weld line was spherical while two different morphologies in the weld line of PS/PMMA (50/50) were observed. And the stripe‐like morphology of PS perpendicular to the flow direction in the weld line of PS/PMMA (20/80) is responsible for the little effect of ultrasonic oscillations. The fractured surfaces of PS, PMMA, and PS/PMMA (80/20) with weld line became much rougher due to the introduction of ultrasonic oscillations. The morphology study of PS/PMMA (80/20) showed that the spherical dispersed phase of PS/PMMA at the skin turned smaller under ultrasonic oscillations. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2990–2997, 2006     

The morphology and mechanical properties of dynamic packing injection molded PP/PS blends

As a part of long-term project aimed at super polyolefin blends, in this work, we report the mechanical reinforcement and phase morphology of the immiscible blends of polypropylene (PP) and polystyrene (PS) achieved by dynamic packing injection molding (DPIM). The shear stress (achieved by DPIM) and interfacial interaction (obtained by using styrene-butadiene-styrene (SBS) as a compatibilizer) have a great effect on phase morphology thus mechanical properties. The shear-induced morphology with core in the center and oriented zone surrounding the core was observed in the cross-section areas of the samples. The phase inversion was also found to shift towards lower PS content under shear stress, at 70 wt% in the core and 30 wt% in the oriented zone, compared with 80 wt% for static samples (without shear). The tensile strength, tensile modules and impact strength were found largely increase by means of either shear stress or compatibilizer. The PS particle size is greatly reduced with adding of SBS, and the reduced particle size results in greater resistance to deformation, which causes the co-continuous structure at oriented zone change into droplet morphology. The morphology resulting from blending and processing was discussed based on effect of interfacial tension, shear rate, phase viscosity ratio and composition. The observed change of mechanical properties was explained based on the combined effect of phase morphology (droplet-matrix or co-continuous phase) and molecular orientation under shear stress.     

PS/PMMA共混物中超声波传播特性研究

利用自行设计的装置,采用改变入射角的方法将超声波纵波和横波导入不相容的聚苯乙烯/聚甲基丙烯酸甲酯(PS/PMMA)共混物体系中。研究了两种波的声速和声衰减随共混体系共混比变化的情况,并结合扫描电子显微镜(SEM)检测得到的相畴尺寸进行了分析。结果表明:共混物中的相畴尺寸与其散射衰减之间存在对应关系;由于横波波长更为接近共混体系中的相畴尺寸,横波的散射衰减明显大于纵波。     

Compatibilization Mechanism of Nanoclay in Immiscible PS/PMMA Blend Using Unmodified Nanoclay

Organically modified nanoclays have been reported to play the role of a compatibilizer for immiscible polymer blends. However, the mechanism of compatibilization by nanoclay has been reported differently. In this work, we investigated the exact mechanism of compatibilization of nanoclay in immiscible polystyrene (PS)/poly(methyl methacrylate) (PMMA) blend in the presence of sodium-montmorillonite (Na-MMT) through selective dispersion of clay in the matrix phase. Through a detailed investigation of the morphology of PS/PMMA/Na-MMT blend nanocomposites, the plausible mechanism behind the compatibilization effect of clay in immiscible blends has been proposed.     

不同PMMA对ABS/PMMA合金性能的影响

试验采用两种不同的聚甲基丙烯酸甲酯 (PMMA)与ABS进行共混。并对ABS/PMMA共混物的各项性能进行了较详细的研究。试验结果表明 ,不同分子量的PMMA对ABS/PMMA混合物的光学性能、力学性能以及流变行为都有显著不同的影响     

Comparison of hydrogen bonding interaction between PMMA/PMAA blends and PMMA-co-PMAA copolymers

A series of miscible PMMA/PMAA blends and PMMA-co-PMAA copolymers with different compositions were prepared in this study. T_gs of PMMA-co-PMAA copolymers are significantly higher than average values or from the Fox equation. The proton spin-lattice relaxation time in the rotating frame (T_1ρ^H) determined by high resolution solid state ¹³C nuclear magnetic resonance indicates single composition-dependent from all blends and copolymers, implying a good miscibility with chain dynamics on a scale of 1-2 nm. However, T_1ρ^Hs of copolymers are still smaller than those of blends, implying that degrees of homogeneity of copolymers are higher than those of blends. On the basis of Kovacs' free volume theory, the free volume of the copolymer obtained is decreased which is another indication of greater homogeneity of the copolymer than that of the corresponding blend. According to Fourier transform infrared spectroscopy analyses, the above results can be rationalized that the hydrogen bonding interaction of the copolymer is stronger than the blend.     

A modified rheological model of viscosities for BR–SBS blends

Blends of polybutadiene (BR) and styrene–butadiene–styrene triblock copolymer (SBS) have been prepared by a two‐roll mill. The morphologies of extruded samples from a capillary rheometer were observed by scanning electron microscopy (SEM). It is found that PS phase is dispersed in the BR phase. The glass transition temperature (T_g) of the blend has been examined by using differential scanning calorimetry (DSC). From the T_g behavior and the electron microscopy study, it is found that certain degree of miscibility between the polystyrene phase and the BR phase is observed. The rheological behavior of the blend has been investigated by a capillary rheometer. It is found that the viscosity of the blend increases with increased content of PS phase. The behavior is in accord with the expected behavior of filler effect. To predict the filler effect of PS phase on the BR–SBS blend, a modified model of Chen and Cheng is proposed to elucidate the rheological properties of the BR–SBS blends with different compositions. Chen and Cheng's micromechanical model derived in Part I of this series, which relates the macroscopic shear stress to the macroscopic shear rate of a rigid non‐Newtonian suspension when the direct contribution of Brownian force is completely neglected. The agreement between the theoretical predictions and the experimental results is satisfactory. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 39–46, 1999     

Precipitation of PMMA/PCL blends using supercritical carbon dioxide

Solutions of a poly(methyl methacrylate)–poly(ε‐Caprolactone) (PMMA/PCL) polymer blend in dichloromethane (DCM) and mixtures of the same polymer blend and cholesterol in DCM were sprayed into supercritical carbon dioxide. Carbon dioxide was contacted with 0.23–1 wt % polymer solutions and with 0.3–1 wt % polymer plus 0.1–0.6 wt % cholesterol solutions in a continuous mode of operation. Pressure and temperature were constant for almost all of the experiments, 11 MPa and 314 K, respectively. Fibrous networks composed of many smaller microfibrils were obtained by spraying the different solutions through a conical nozzle into concurrently flowing supercritical carbon dioxide. This morphology suggests such an important degree of agglomeration that primary particles are no longer discernible. Processing the polymers with CO₂ leads to the removal of contaminants as the precipitate was free of monomer and initiator. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2422–2426, 2004     

Dendritic crystallization in thin films of PEO/PMMA blends: A comparison to crystallization in small molecule liquids

Dendritic crystallization of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) thin films is reported. The film thickness is kept constant while the PMMA molar mass and blend composition are varied. Some basic features of dendritic growth, such as the diffusion length and tip curvature are discussed. The diffusion coefficient is tuned by varying the molar mass of the non-crystallizable PMMA and the blend composition. The observed dendrite tip radius is on the order of 50 nm and the shape of the growth envelope varies from square to needle-like as the PMMA molar mass or PMMA content is increased. The sidebranch spacing increases with the distance from the dendrite trunk with a power-law relationship that is also dependent on the PMMA molar mass and PMMA content. This coarsening process is similar to that reported for other classes of materials. These similarities (the curved dendrite tip, power-law relationship of the sidebranches, and the sidebranch coarsening processes) indicate that the large scale crystallization morphologies of the polymeric materials we study are similar to those found in crystallization of small molecules and metals.     

Study of PS/SBS/nano-CaCO3 blends

Abstract

The effect of SBS and nano-CaCO₃ on the mechanical properties of PS blends was studied, and their morphologies were characterised by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Izod impact strengths of notched samples of PS/SBS/CaCO₃ blends with nanometre particles of nano-CaCO₃ and SBS are higher than those of PS and PS/SBS blends with the same content of SBS, and the tensile strengths are higher than those of PS/SBS blends. The inclusion of nano-CaCO₃ within the dispersed phase of SBS enlarges the volume of the domains of SBS, which increases the toughness of the ternary blends (PS/SBS/CaCO₃). The mass ratio of SBS/CaCO ₃ plays an important role in the properties of the ternary blends because it affects the concentration of SBS in these blends, the dispersion of nano-CaCO₃ and the morphology of the ternary blends.     

On the interactions and miscibility of PVC/PMMA blends

A DSC thermogram showed two separate glass transition temperatures in PVC/PMMA mixtures over the entire composition range; multiphase structures were observed in an optical microscope. FTIR spectra indicate that there are no strong specific interactions between these two polymers. The earlier studies on this blend system are briefly reviewed.     

Weldline strength in injection molded HDPE/PA6 blends: Influence of interfacial modification

Most injection molded objects contain defects known as weldlines. This defect may introduce an element of weakness affecting the object's performance. Weldlines are particularly problematic in multiphase materials where the situation may be exaggerated by component mismatch on the two sides of the interface that results in additional weakening when the two components do not adhere well to each other. In addition, weldline behavior is influenced by orientation and morphological effects. This paper deals with relationships between the structure and the mechanical properties in injection molded high density polyethylene polyamide-6 blends. The weldline effect is investigated in detail. Two molds were used to generate weldlines: a double-gated tensile bar cavity in which the weldline results from the meeting of two melt fronts flowing into each other from opposite directions, and a film-gated rectangular plaque mold with a circular insert that divides the melt front in two. Following the recombination of the fronts, there is additional flow as the melt fills the mold cavity. Two preparations containing 75 vol % of polyamide-6 and 25 vol % of polyethylene with and without compatibilizer were studied. In the first case, a compatibilizer was incorporated into the polyethylene prior to compounding with the polyamide-6. In the directly molded tensile bar the minor phase is strongly oriented parallel to flow. Only in the core, which represents about 10% of the sample thickness, do the dispersed phase particles assume spherical shape. The morphology of the weldline is closely related to that of the skin: the elongated structures are oriented parallel to the weldline plane. The effect of the compatibilizer on the mechanical properties (without the weldline) of the directly molded tensile bars is minor: It is overshadowed by the flow-induced morphology. The weldline strength loss is about 40% in the noncompatibilized blend. The introduction of the compatibilizer has restored the material's ability to yield and the properties are close to those measured without the weldline. For the second type mold, the effect of the weldline is less pronounced and the effect of the distance from the insert is negligible. The anisotropy is quite pronounced in the noncompatibilized blend. In compatibilized blends, all tensile properties are unaffected by the presence of weldline, except for the 2-mm-thick plaque in the position close to the insert. The properties in the direction parallel to flow are similar to the type I mold and not affected by the increase of plaque thickness. Consequently one may question the utility of the directly molded tensile specimens in studying various aspects of the mechanical behavior of multiphase materials where the flow-generated structure is very different from that found in “real” injection molded parts. © 1995 John Wiley & Sons, Inc.     

Surface feature size of spin cast PS/PMMA blends

Thin films of polystyrene (PS)/polymethylmethacrylate (PMMA) blends have been spin cast on mica from chloroform solutions. When the concentration of PMMA in the casting solution is less than that of PS a pitted morphology is formed. The average sizes of the pits are shown to increase with both the total concentration of the casting solution and the relative concentration of PMMA. The change in pit size is explained in terms of incomplete dewetting of a PMMA solution from an underlying PS solution. For a given ratio of PMMA/PS the average pit diameters appear to increase linearly with the square of the film thickness, the gradient of which is dependent on the film composition.     

Microwave-assisted processing of silicone/PMMA blends for maxillofacial prostheses

Maxillofacial prostheses replace soft tissues that were lost due to disease or trauma, providing the restoration of the original anatomy and protecting the injured tissue. Silicone is the most widely used material, but the crosslinking process usually takes 24 hours to be completed. In this study, silicone/poly(methyl-methacrylate) blends were prepared at room temperature and assisted by microwave irradiation. The samples were characterized by confocal Raman microscopy and scanning electron microscopy/energy-dispersive X-ray spectroscopy. The microwave-assisted crosslinking is completed within 10 minutes and leads to better adhesion between silicone and PMMA than samples processed at room temperature. The methodology was adapted for the fabrication of prostheses for 50 patients with an average lifetime of 3 years, which is higher than the averages reported earlier in the literature (6-24 months).     

The Effect of Multiple Compatibilizers on the Impact Properties of Polypropylene/Polystyrene (PP/PS) Blend

Effects of compatibilizers on impact properties of polypropylene/ polystyrene (PP/PS) blends were studied and carried out through melt blending using co- rotating twin-screw extruder. A combination of two compatibilizers, maleic anhydride grafted polypropylene (PP-g-MA) and styrene maleic anhydride (SMA) was applied into PP/PS blends. Results from the Izod impact strengths, SEM observations and contact angle measurements in PP(50)/PS(50) blends indicated a better compatibilization effect with the use of dual compatibilizers. This was most probably due to improved adhesion between phases in PP/PS blend systems. The use of dual compatibilizers in the blend compositions produced higher impact properties in the PP/PS blend systems compared to single compatibilizer system.     

A study on weld line morphology and mechanical strength of injection molded polystyrene/poly(methyl methacrylate) blends

In this work, the mechanical strength and weld line morphology of injection molded polystyrene/poly(methyl methacrylate) (PS/PMMA) blends were investigated by scanning electron microscopy (SEM) and mechanical property test. The experimental results show that the tensile strength of PS/PMMA blends get greatly decreased due to the presence of the weld line. Although the tensile strength without the weld line of PS/PMMA (70/30) is much higher than that of the PS/PMMA (30/70) blend, their tensile strength with weld line shows reversed change. The viscosity ratio of dispersed phase over matrix is a very important parameter for control of weld‐line morphology of the immiscible polymer blend. In PS/PMMA (70/30) blend, the PMMA dispersed domains at the core of the weld line are spherically shaped, which is the same as bulk. While in the PS/PMMA (30/70) blend, the viscosity of the dispersed PS phase is lower than that of the PMMA matrix, the PS phase is absent at the weld line, and PS particles are highly oriented parallel to the weld line, which is a stress concentrator. This is why weld line strength of PS/PMMA (30/70) is lower than that of PS/PMMA (70/30) blend. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1856–1865, 2002; DOI 10.1002/app.10450     

Effect of composition on the linear viscoelastic behavior and morphology of PMMA/PS and PMMA/PP blends

Here, the effect of concentration on the morphology and dynamic behavior of polymethylmethacrylate/polystyrene (PMMA/PS), for PS with two different molecular weight, and polymethylmethacrylate/polypropylene (PMMA/PP) blends was studied. The blends concentrations ranged from 5% to 30% of the dispersed phase (PS or PP). The dynamic data were analyzed to study the possibility of inferring the interfacial tension between the components of the blend from their rheological behavior using Palierne [Palierne JF. Rheol Acta 1990;29:204-14] [1] and Bousmina [Bousmina M. Acta 1999;38:73-83] [2] emulsion models. The relaxation spectrum of the blends was also studied. The dynamic behavior of 85/15 PS/PMMA blend were studied as a function of temperature. It was possible to fit both Palierne and Bousmina's emulsion models to the dynamic data of PMMA/PS blends, to obtain the interfacial tension of the blend. This was not the case for PMMA/PP. The relaxation spectrum of both blends was used to obtain the interfacial tension between the components of the blends. The values of interfacial tension calculated were shown to decrease when the concentration of the blends increased. It was shown using morphological analysis that this phenomenon can be attributed to the coalescence of the dispersed phase during dynamic measurements that occurs for large dispersed phase concentration. When the ‘coalesced’ morphology is taken into account in the calculations the interfacial tension inferred from rheological measurement did not depend on the concentration of the blend used. The values of interfacial tension found analyzing the dynamic behavior of one of the PMMA/PS blend were shown to decrease with temperature.     

Dependence of impact strength on the fracture propagation direction in dynamic packing injection molded PP/EPDM blends

In order to further understand the brittle-ductile (B-D) transition in PP/EPDM blends, a shear stress field achieved via dynamic packing injection molding was used to control the rubber particles as elongated and orientated in the PP matrix. The impact strength of the blends was measured in three fracture directions, namely, along the shear flow direction, perpendicular to and oblique (45°) with the flow direction. A definite B-D transition of impact strength was found at 20 wt% of EPDM content along the shear flow direction. About 10 times increase of impact strength was observed at the B-D transition. However, a B-D transition and then a decrease of impact strength brittle-ductile-brittle (B-D-B) was found as increasing of EPDM content in the impact direction perpendicular to and oblique with the flow direction. One observes a big increase of impact strength at 20-30 wt% of EPDM content (B-D transition) from 10-20 to 70-80 kJ/m², then a sharp decrease of impact strength is seen when EPDM content reaches to 30-45 wt% (D-B transition) from 70-80 to 40-50 kJ/m². Correspondingly, there exists a change of rubber particles from roughly spherical shape to highly elongated and oriented shape at D-B transition. SEM shows a very smooth fractured surface when fracture propagation is along or oblique with the shear flow direction, but a lay-by-layer fracture behavior when fracture propagation is perpendicular to the shear flow direction. Our results suggest that the impact fracture direction with respect to the orientation direction play an important role to determine the impact strength. Wu's theory holds true as long as the rubber particles are roughly spherical when viewed in the same direction with fracture propagation direction, but no longer valid when dispersed rubber particles are elongated and oriented when viewed in the direction perpendicular to or oblique with the fracture propagation direction.     

Improvement of mechanical properties for PP/PS blends by in situ compatibilization

The effect of the in situ compatibilization on the mechanical properties of PP/PS blends was investigated. The application of Friedel-Crafts alkylation reaction to the PP/PS-blend compatibilization was assessed. Styrene/AlCl₃ was used as catalyst system. The graft copolymer (PP-g-PS) formed at the interphase showed relatively high emulsifying strength. Scission reactions, occurring in parallel with grafting, were verified for PP and PS at high catalyst concentration, but no crosslinking reactions were detected. Tensile tests were performed on dog-bone specimens of the blends. Both elongation at break and toughness increased with catalyst concentration. At 0.7% AlCl₃, a maximum was reached, which amounted to five times the value of the property for the uncompatibilized blend. At higher catalyst concentrations these properties decreased along with the PP molecular weight due to chain-scission reactions. On the other hand, the tensile strength did not change with the catalyst concentration. The in situ compatibilized blends showed considerable improvement in mechanical properties, but were adversely affected by chain scissions at high catalyst contents.     

Effect of matrix composition on the fracture behavior of rubber-modified PMMA/PVC blends

Summary PB-g-MMA core-shell impact modifiers were synthesized by seed emulsion polymerization and impact-modified PMMA/PVC blends were prepared by melt blending PMMA, PVC and PB-g-MMA at 160 °C. The PB-g-MMA particles were dispersed uniformly in the PMMA/PVC matrix. PMMA/PVC blends were prepared in the blend ratio from 100/0 to 0/100 and the rubber content was kept 16% in all the compositions. The effects of matrix composition on the mechanical properties and morphology of the blends were studied. It was found that when the matrix was a PMMA-rich system, the sample broke in a brittle mode and crazing of the matrix was the main mechanisms of deformation. When the matrix was a PVC-rich system, the sample broke in a ductile mode and the main deformation mechanisms were cavitation of the particle and shear yielding of the matrix. There existed a transition from crazing to shear yielding in the rubber-modified PMMA/PVC blend as the matrix composition varied.