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     

Ultrasonic improvement of weld line strength of injection‐molded polystyrene and polystyrene/polyethylene blend parts

The effect of melt temperature, ultrasonic oscillations, and induced ultrasonic oscillations modes on weld line strength of polystyrene (PS) and polystyrene/polyethylene (PS/HDPE) (90/10) blend was investigated. The results show that the increase of melt temperature is beneficial to the increase of weld line strength of PS and PS/HDPE blend. Compared with PS, the increase of melt temperature can greatly enhance the strength of PS/HDPE blends. For PS, the presence of ultrasonic oscillations can enhance the weld line strength of PS at different melt temperatures. But for PS/HDPE blends, the presence of ultrasonic oscillations can improve the weld line strength when the melt temperature is 230°C, but when the melt temperature is 195°C, the induced ultrasonic oscillations hardly enhance the weld line strength. Compared with Mode I (ultrasonic oscillations were induced into the mold at the whole process of injection molding), the induced ultrasonic oscillations as Mode II (ultrasonic oscillations were induced into the mold after injection mold filling) is more effective at increasing the weld line strength of PS and PS/HDPE blends. The mechanism for ultrasonic improvement of weld line strength was also studied. POLYM. ENG. SCI., 45:1666–1672, 2005. © 2005 Society of Plastics Engineers     

A modified model predictions and experimental results of weld-line strength in injection molded PS/PMMA blends

In this paper, the model based on melt diffusion and Flory-Huggins free energy theory for predicting the weld-line strength of injection molded amorphous polymers and polymer blends parts were modified by considering the diffusion thickness in the interface as a function of contact time. The modified model for weld-line strength prediction of homopolymers and polymer blends were, respectively, used to evaluate the weld-line strength of Polystyrene (PS) and Poly(methylmethacrylate) (PMMA), and that of PS/PMMA blends. The model predictions show that the theoretic predictions as a function of temperature and contact time for PS, PMMA and PS/PMMA (80/20, 70/30) are in good agreements with corresponding experimental results. However, the model predictions for PS/PMMA (20/80, 30/70) blends are much higher than experimental results. The morphology in weld-line regions for PS/PMMA (20/80, 30/70) shows lack of dispersed PS phase. Near the weld-line regions, dispersed PS phase is highly oriented along the weld-line. In theoretic prediction for polymer blends, three kinds of diffusion: Polymer A-Polymer A and Polymer B-Polymer B self-diffusions and Polymer A-Polymer B mutual diffusion were considered. This is why model predictions for PS/PMMA (20/80, 30/70) blends are higher than experimental results.     

Weld‐line characteristics of polycarbonate/acrylonitrile–butadiene–styrene blends. I. Effect of the processing temperature

The effects of the processing temperature on the morphology and mechanical properties at the weld line of 60/40 (w/w) polycarbonate (PC)/acrylonitrile–butadiene–styrene (ABS) copolymer blends were investigated. The influences of the incorporation of poly(methyl methacrylate) (PMMA) as a compatibilizer and an increase in the viscosity of the dispersed ABS domain phase were also studied. The ABS domain was well dispersed in the region below the V notch, and a coarse morphology in the core region was observed. When tensile stress was applied perpendicularly to the weld line, the fracture propagated along the weak region behind the weld part; there, the domain phase coalescence was significant because of the poor compatibility between PC and styrene–acrylonitrile (SAN). Phase coalescence became severe, and so the mechanical strength of the welded specimen decreased with an increasing injection‐molding temperature. The domain morphology became stable and the mechanical strength increased as the viscosity of the domain phase increased or some SAN was replaced with PMMA. That the morphology was well distributed behind the weld line and the mechanical properties of PC/ABS/PMMA blends were improved was attributed to the compatibilizing effect of PMMA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 689–699, 2005     

Ultrasonic improvement of the compatibility and rheological behavior of high‐density polyethylene/polystyrene blends

The effects of ultrasonic oscillations on the rheological behavior, mechanical properties, and morphology of high‐density polyethylene (HDPE)/polystyrene (PS) blends were studied. The experimental results show that the die pressure and apparent viscosity of HDPE/PS blends are remarkably reduced in the presence of ultrasonic oscillations and that mechanical properties of the blends are improved. The particle size of the dispersed phase in HDPE/PS blends becomes smaller, its distribution becomes narrower, and the interfacial interaction of the blends becomes stronger if the blends are extruded in the presence of ultrasonic oscillations. Ultraviolet spectra and Soxhlet extraction results show the formation of a polyethylene‐PS copolymer during extrusion in the presence of ultrasonic oscillations, which improves the compatibility of HDPE/PS blends. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 23–32, 2002     

Investigation on particular morphology of immiscible polyamide 12/polystyrene blends

In this article, a particular phase morphology of immiscible polyamide 12/polystyrene (PA12/PS) blends prepared via in situ anionic ring-opening polymerization of Laurolactam (LL) in the presence of PS was investigated. SEM and FTIR were used to analyze the morphology of the blends. The results showed that PS is dispersed as small droplets in the continuous matrix of PA12 when PS content is less than 5 wt %. When the PS content is higher than 10 wt %, two particular phase morphologies appeared. First, dispersed PS-rich particles with the spherical inclusions of PA12 can be found when PS content is between 10 wt % and 15 wt %. Then, the phase inversion (the phase morphology of the PA12/PS blends changes from the PS dispersed/PA12 matrix to PA12 dispersed/PS matrix system) occurred when PS content is higher than 20 wt %, which is completely different from traditional polymer blends prepared by melt blending. The possible reason for the particular morphology development was illuminated through phase inversion mechanism. Furthermore, the stability of the phase morphologies of the PA12/PS blends was also investigated. SEM showed that the particular morphology is instability, and it will be changed upon annealing at 230°C for 30 min. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Investigation on particular phase morphology of immiscible polyamide 12 and polystyrene blends prepared via anionic ring‐opening polymerization

In this article, the particular phase morphology of immiscible polyamide 12/polystyrene (PA12/PS) blends prepared via in situ anionic ring‐opening polymerization of laurolactam (LL) in the presence of polystyrene (PS) was investigated. Scanning electron microscopy (SEM) and Fourier Transform infrared Spectroscopy (FTIR) were used to analyze the morphology of the blends. The results show that the PS is dispersed as small droplets in the continuous matrix of PA12 when PS content is 5 wt%. However, when the PS content is higher than 10 wt%, two particular phase morphologies appeared. Firstly, dispersed PS‐rich particles with the spherical inclusions of PA12 can be found when PS content is between 10 and 15 wt%. Then the phase inversion occurred (the phase morphology of the PA12/PS blends changed from the PS dispersed/PA12 matrix to PA12 dispersed/PS matrix system) when PS content is 20 wt% or higher, which is unusual for polymer blends prepared via conventional methods such as mixing, hydrolytic polycondensation and so on. The formation of this particular phase morphology development was simply elucidated via a phase inversion mechanism. Furthermore, the stability of the phase morphology of the PA12/PS blends after annealing at 230°C was also investigated via SEM. POLYM. ENG. SCI., 52:1831–1838, 2012. © 2012 Society of Plastics Engineers     

Dynamic rheological properties of high‐density polyethylene/polystyrene blends extruded in the presence of ultrasonic oscillations

The linear rheological properties of high‐density polyethylene (HDPE), polystyrene (PS), and HDPE/PS (80/20) blends were used to characterize their structural development during extrusion in the presence of ultrasonic oscillations. The master curves of the storage shear modulus (G′) and loss shear modulus (G″) at 200°C for HDPE, PS, and HDPE/PS (80/20) blends were constructed with time–temperature superposition, and their zero shear viscosity was determined from Cole–Cole plots of the out‐of‐phase viscous component of the dynamic complex viscosity (η″) versus the dynamic shear viscosity. The experimental results showed that ultrasonic oscillations during extrusion reduced G′ and G″ as well as the zero shear viscosity of HDPE and PS because of their mechanochemical degradation in the presence of ultrasonic oscillations; this was confirmed by molecular weight measurements. Ultrasonic oscillations increased the slopes of log G′ versus log G″ for HDPE and PS in the low‐frequency terminal zone because of the increase in their molecular weight distributions. The slopes of log G′ versus log G″ for HDPE/PS (80/20) blends and an emulsion model were used to characterize the ultrasonic enhancement of the compatibility of the blends. The results showed that ultrasonic oscillations could reduce the interfacial tension and enhance the compatibility of the blends, and this was consistent with our previous work. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3153–3158, 2004     

Structured latex particles based on natural rubber for high-impact polymer blends

Natural latex (NR) particles, modified with a hard shell of poly(methyl methacrylate) (PMMA) and with a substructure of PMMA (type "NR-M") or polystyrene (type "NR-SM"), were tested as compatibilizers in blends of polycarbonate (of bisphenol A, PC) and PMMA or PS. During melt blending, the modified NR particles were torn apart, from an original size of >0.5 μm down to ≅0.1 μm in diameter. Two different types of particle distribution were observed in the blends: in PC/PMMA/NR-M blends, the NR-M particles were dispersed in the PMMA phase, whereas, in PC/PS/NR-SM blends, the NR-SM particles formed interface layers between PC and PS phase domains. The latter blend morphology, distinguished by continuous rubbery interface layers of NR-SM, turned out to be mechanically excellent in injection-moulded parts. The poor impact strength of PC/PS was raised by an order of magnitude. The effect depends on the orientation in the injection-moulded test bars.     

Ethylene Methacrylate (EMA) Co-polymer Toughened Polymethyl Methacrylate Blends: Physico-mechanical,Optical, Thermal and Chemical Properties

Polymethyl methacrylate (PMMA) was blended with ethylene methacrylate (EMA) copolymer in different compositions by melt mixing technique using Haake Rheochord twin screw extruder. The physico-mechanical, thermal, optical and chemical properties of PMMA/EMA blends were investigated with special reference to the blend compositions. The impact strength of the blends was found to increase significantly with increase in EMA content, without affecting the optical properties significantly. Optical micrograph images of the blends reveals that the rubbery phase dispersed as domains in the continuous PMMA matrix at 5 and 10 wt. % addition of EMA. The PMMA/EMA, 80/20 blend was found to exist as co-continuous system. Attempts have been made to correlate changes in morphology with mechanical properties. The influence of chemical ageing and heat ageing on the mechanical performance of PMMA/EMA blends has been studied. Four composite models such as series model, parallel model, Hapin-Tsai and Kerner's model have been used to fit the experimental tensile strength, tensile modulus and surface hardness.     

Thermal and mechanical properties of poly(methyl methacrylate) and ethylene vinyl acetate copolymer blends

A series of poly(methyl methacrylate) (PMMA) blends have been prepared with different compositions viz., 5, 10, 15, and 20 wt % ethylene vinyl acetate (EVA) copolymer by melt blending method in Haake Rheocord. The effect of different compositions of EVA on the physico‐mechanical and thermal properties of PMMA and EVA copolymer blends have been studied. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) has been employed to investigate the phase behavior of PMMA/EVA blends from the point of view of component specific interactions, molecular motions and morphology. The resulting morphologies of the various blends also studied by optical microscope. The DSC analysis indicates the phase separation between the PMMA matrix and EVA domains. The impact strength analysis revealed a substantial increase in impact strength from 19 to 32 J/m. The TGA analysis reveals the reduction in onset of thermal degradation temperature of PMMA with increase in EVA component of the blend. The optical microscope photographs have demonstrated the PMMA/EVA system had a microphase separated structure consisting of dispersed EVA domains within a continuous PMMA matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

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.     

SEBS/PPO共混物的相态结构及力学性能和流变性能 研究

将不同配比的苯乙烯-乙烯-丁二烯-苯乙烯嵌段共聚物（SEBS）/聚苯醚 （PPO）通过同向双螺杆挤出机进行熔融共混。应用原子力显微镜（AFM）观察了SEBS/PPO不同配比的相态结构,并比较了其力学性能,同时还比较了不同充油量的SEBS/PPO共混物的相态结构、力学性能和流变性能。结果表明,随着PPO含量的增加,亮点聚苯乙烯（PS）段逐渐增加,PPO和PS完全融合到一起,当SEBS/PPO＝80/20时乙烯-丁二烯（EB）段是连续相,PS相和PPO是分散相;当SEBS/PPO＝20/80时发生相反转,PPO变为连续相;随着PPO含量的增加,拉伸强度大幅度增加,断裂伸长率明显降低;随着充油量的增加,拉伸强度和断裂伸长率均有不同程度的下降;表观黏度随非牛顿剪切速率的增加逐渐降低。     

Nanostructured polymer blends based on polystyrene‐b‐polybutadiene‐b‐poly(methyl methacrylate) triblock copolymers modified with polystyrene and/or poly(methyl methacrylate) homopolymers

Morphologies of polymer blends based on polystyrene‐b‐ polybutadiene‐b ‐poly(methyl methacrylate) (SBM) triblock copolymer were predicted, adopting the phase diagram proposed by Stadler and co‐workers for neat SBM block copolymer, and were experimentally proved using atomic force microscopy. All investigated polymer blends based on SBM triblock copolymer modified with polystyrene (PS) and/or poly(methyl methacrylate) (PMMA) homopolymers showed the expected nanostructures. For polymer blends of symmetric SBM‐1 triblock copolymer with PS homopolymer, the cylinders in cylinders core?shell morphology and the perforated lamellae morphology were obtained. Moreover, modifying the same SBM‐1 triblock copolymer with both PS and PMMA homopolymers the cylinders at cylinders morphology was reached. The predictions for morphologies of blends based on asymmetric SBM‐2 triblock copolymer were also confirmed experimentally, visualizing a spheres over spheres structure. This work presents an easy way of using PS and/or PMMA homopolymers for preparing nanostructured polymer blends based on SBM triblock copolymers with desired morphologies, similar to those of neat SBM block copolymers. © 2017 Society of Chemical Industry     

Composite droplets with core/shell morphologies prepared from HDPE/PS/PMMA ternary blends by twin‐screw extrusion

Ternary blends of PS and PMMA in a PE matrix were prepared by twin‐screw extrusion to investigate the core/shell encapsulation phenomenon in the composite droplet. The PS was found to encapsulate the PMMA to form composite droplets within the PE matrix as expected from the spreading coefficient theory. The effects of dispersed phase concentration, viscosity ratio, feeding sequence and twin‐screw operating conditions were investigated. The blend morphology was observed by scanning electron microscopy after selective extraction of either PS or PMMA, and average core and composite droplet diameters were determined by image analysis. Although it is known that the structure of composite droplet blends can be substantially altered through control of the volume fraction of the components in the dispersed phase, this study demonstrates that blends with a 1:1 composite droplet volume fraction are relatively stable to large variations in the minor phase viscosities and processing conditions. Twin‐screw extrusion thus provides a highly robust technique for the melt processing of blends possessing composite droplet morphologies. Polym. Eng. Sci. 44:749–759, 2004. © 2004 Society of Plastics Engineers.     

Effect of mixing protocol on compatibilized polymer blend morphology

We investigated the effect of mixing protocol on the morphology of compatibilized polymer blends made with premade compatibilizer and reactively formed in‐situ compatibilizer in a custom‐built miniature mixer Alberta Polymer Asymmetric Minimixer (APAM). The compatibilized blends show a finer morphology than uncompatibilized blends if the polymers are mixed together in the dry state and then fed into the mixer. It is found that premelting one polymer, and premixing polymers and compatibilizer, both greatly affect the compatibilized blends' morphology. The effects are complex since the dispersed phase particle size and distribution of the compatibilized blends may be smaller or larger when compared with the uncompatibilized system, depending on the material's physical and chemical properties; for example, diblock molecular weight or the preference of copolymer to migrate to a particular phase can change the final morphology. Good mobility of the copolymer to reach the interface is crucial to obtain a finer morphology. Micelles are observed when a high molecular weight diblock copolymer P(S‐b‐MMA) is used for a PS/PMMA blend. Because of its enhanced mobility, no micelles are found for a low molecular weight diblock copolymer P(S‐b‐MMA) in a PS/PMMA blend. For PS/PE/P(S‐b‐E) blends, finer morphology is obtained when P(S‐b‐E) is first precompounded with PS. Because the block copolymer prefers the PE phase, if the P(S‐b‐E) block copolymer is compounded with PE first, some remains inside the PE phase and does not compatibilize the interface. In the case of reactive blend PSOX/PEMA, premelting and holding the polymers at high temperature for 5 min decreases final dispersed phase particle size; however, premelting and holding for 10 min coarsens the morphology. POLYM. ENG. SCI. 46:691–702, 2006. © 2006 Society of Plastics Engineers.     

Phase morphology,thermomechanical, and crystallization behavior of uncompatibilized and PP‐g‐MAH compatibilized polypropylene/polystyrene blends

In this article, we discuss the phase morphology, thermal, mechanical, and crystallization properties of uncompatibilized and compatibilized polypropylene/polystyrene (PP/PS) blends. It is observed that the Young's modulus increases, but other mechanical properties such as tensile strength, flexural strength, elongation at break, and impact strength decrease by blending PS to PP. The tensile strength and Young's modulus of PP/PS blends were compared with various theoretical models. The thermal stability, melting, and crystallization temperatures and percentage crystallinity of semicrystalline PP in the blends were marginally decreased by the addition of amorphous PS. The presence of maleic anhydride‐grafted polypropylene (compatibilizer) increases the phase stability of 90/10 and 80/20 blends by preventing the coalescence. Hence, finer and more uniform droplets of PS dispersed phases are observed. The compatibilizer induced some improvement in impact strength for the blends with PP matrix phase, however fluctuations in modulus, strength and ductility were observed with respect to the uncompatibilized blend. The thermal stability was not much affected by the addition of the compatibilizer for the PP rich blends but shows some decrease in the thermal stability of the blends, where PS forms the matrix. On the other hand, the % crystallinity was increased by the addition of compatibilizer, irrespective of the blend concentration. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42100.     

Polypropylene‐dispersed domain as potential nucleating agent in PS and PMMA solid‐state foaming

The potential of using dispersive domains in a polymer blend as a bubble nucleating agent was investigated by exploiting its high dispersibility in a matrix polymer in the molten state and its immiscibility in the solid state. In this experiments, polypropylene (PP) was used as the nucleating agent in polystyrene (PS) and poly(methyl methacrylate) (PMMA) foams at the weight fraction of 10, 20, and 30 wt %. PP creates highly dispersed domains in PS and PMMA matrices during the extrusion processing. The high diffusivity of the physical foaming agent, i.e., CO₂ in PP, and the high interfacial tension of PP with PS and PMMA could be beneficial for providing preferential bubble nucleation sites. The experimental results of the pressure quench solid‐state foaming of PS/PP and PMMA/PP blends verified that the dispersed PP could successfully increase the cell density over 10⁶ cells/cm³ for PS/PP and 10⁷ cells/cm³ for PMMA/PP blend and reduce the cell size to 24 μm for PS/PP and 9 μm for PMMA/PP blends foams. The higher interfacial tension between PP and the matrix polymer created a unique cell morphology where dispersed PP particles were trapped inside cells in the foam. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

拉曼Mapping成像研究聚苯乙烯/聚甲基丙烯酸甲酯共混体系的相态结构

利用拉曼光谱成像技术研究了聚苯乙烯/聚甲基丙烯酸甲酯（PS/PMMA）共混薄膜体系及其增容体系（增容剂为PS-b-PMMA嵌段共聚物）的相态结构及化学成分分布。实验结果表明,拉曼Mapping成像技术不仅可以得到PS/PMMA共混体系化学成分的精确分布图,同时也可以获取共混体系中分散相、界面相和连续相的分子指纹光谱。研究发现,共混体系中分散相和连续相组分分布与体系的组成紧密相关,当PS/PMMA质量比30/70时,分散相为PS,连续相为PMMA;当PS/PMMA质量比为50/50时,分散相为PS,但PS分子链仍存在于PMMA连续相中;当PS/PMMA质量比为70/30时,分散相为PMMA,连续相为PS。当增容剂PS-b-PMMA加入到PS/PMMA共混体系中后,分散相粒径减小、分布更加均匀、共混体系相容性指数（N_c）增大,说明PS/PMMA共混体系由完全不相容体系趋向变成半相容性体系,这是因为增容剂能增加PS和PMMA之间的相互作用,降低了体系的相分离程度,改善了共混体系的相容性。     

Factors influencing encapsulation behavior in composite droplet-type polymer blends

In this study the influence of the molecular weight of the dispersed phase components on encapsulation effects in the composite droplet phase was examined for high density polyethylene (HDPE)/PS/PMMA ternary blends. Three different blends composed of various PS and PMMA materials dispersed in an HDPE matrix were prepared using an internal mixer. The morphology was studied by light and electron microscopy. Current models used for predicting encapsulation effects and composite droplet formation in ternary systems (based on static interfacial tension) predict in all cases that PS will encapsulate the PMMA. However, in one case, an unexpected encapsulation of PS by PMMA was observed. It was found that arguments based on the effect of viscosity ratio or the absolute viscosity of the different dispersed phases do not explain that discrepancy. In addition, the reversal of that latter composite droplet morphology from PMMA encapsulating PS to PS encapsulating PMMA was observed upon annealing treatment. Considering all the above, a conceptual model was developed to predict encapsulation effects in composite droplet type systems based on the use of a dynamic interfacial tension (i.e. taking into account the elasticity of the polymer components). Calculations based on the dynamic interfacial tension model, using elasticities based on constant shear stress, were able to account for all of the observed encapsulation effects in this study.