Reactive extrusion of polystyrene/polyethylene blends

The feasibility of inducing beneficial changes to polystyrene/polyethylene (PS/PE) blends via reactive extrusion processes is considered. Experiments have been conducted on 50:50 wt.% PS/PE blends that were treated with different levels of dicumyl peroxide and triallyl isocyanurate coupling agent. Both a low molecular weight and a high molecular weight blend series have been investigated. A “more reactive” polystyrene was synthesized by incorporation of a minor amount of ortho-vinylbenzaldehyde. Blends containing this modified polystyrene were subjected to identical processing' conditions on a counter-rotating twin screw extruder. Examination of the tensile properties of the extrusion products suggested that a judicious level of peroxide and coupling agent additives would be beneficial to the ultimate physical properties. The quantity of styrenic phase becoming chemically grafted to the polyethylene matrix was influenced most strongly by the level of the chosen coupling agent. As determined by scanning electron microscopy, the phase morphologies of the tensile test fracture surfaces were strongly dependent upon the reaction extrusion process; those extruded blends that had been exposed to the additive pre-treatment displayed substantially finer microstructure. The enthalpy of fusion of the polyethylene melting endotherm was likewise influenced by both the presence or absence of the additives as well as the molecular weight nature of the blend series.     

In situ reactive compatibilization in polymer blends: Effects of functional group concentrations

Polystyrene (PS) and polyethylene (PE), along with their reactive counterparts, i.e., polystyrene having oxazoline reactive groups (OPS) and polyethylene with carboxylic acid groups (CPE), were melt blended in a Rheomix mixer. These blends were prepared by mixing these polymers in various proportions under a variety of conditions. In an alternate procedure the OPS, CPE graft polymer (OPS-g-CPE) was prepared by melt blending these two polymers beforehand, and subsequently this grafted polymer was used as a compatibilizer for PS–PE blends. The effects of the addition of OPS and CPE, on the one hand, and OPS-g-CPE, on the other hand, on the compatibility of PS–PE blends were investigated. The morphology of these blends was examined with a scanning electron microscope (SEM) and related to their tensile properties. The PS–PE blends are found to have the typical coarse morphology of incompatible blends and poor tensile properties while their reactive counterparts, OPS-CPE blends, have fine grain microstructure and show improved tensile strength throughout the range and improved elongation in the PE-rich blends. Relatively low concentrations of the reactive pair, oxazoline and carboxylic acid, are shown to be necessary to produce improved compatibility. The preblended graft copolymer OPS-g-CPE imparts compatibility to PS–PE blends also but not as effectively. This suggests that the addition of OPS and CPE during melt mixing of PS and PE forms OPS-g-CPE polymer at the interface and that these ingredients act as “in situ reactive compatibilizers” which improve physical properties.     

ABS/PS共混改性研究

采用在材料熔融挤出共混过程中提高双螺杆挤出机螺杆转速的方法,研究了较高螺杆转速条件下双螺杆挤出机的机械剪切应力和弹性体的种类、用量等因素对丙烯腈-丁二烯-苯乙烯共聚物(ABS)/聚苯乙烯(PS)共混材料力学性能和加工流动性能的影响。结果表明,双螺杆挤出机的高剪切应力可促进分散相颗粒的分散和界面结合力的增强,引起共混材料力学性能和熔体流动速率的改善。丁腈橡胶(NBR)粉末对ABS/PS共混材料具有增容增韧作用,挤出共混温度为220℃,螺杆转速在720 r/min,NBR粉末质量分数为10%时,ABS/PS共混材料的缺口冲击强度为16.4 kJ/m2,比改性前约提高1.6倍,达到ABS树脂冲击韧性的指标,并保持了良好的加工流动性。     

Rubber toughening of polystyrene through reactive blending

Acrylonitrile-butadiene rubber having carboxylic acid groups (XNBR) and polystyrene having oxazoline groups, were melt blended in a Rheomix mixer under optimized conditions, The ratio of rubber to polystyrene phase was kept constant at 1:4 by weight. The concentration of the reactive oxazoline groups in the polystyrene phase was varied by mixing polystyrene (PS) with a copolymer of styrene and vinyl oxazoline (OPS). A torque rise observed during blending was found to be related to the concentration of oxazoline-carboxylic acid pairs. This torque rise, and independently measured increases in viscosity, both indicate inter-polymer crosslinkihg. Scanning electron microscopy was used to observe the morphology of the blends. Improved rubber phase dispersion was observed with increasing oxazoline concentration. Instrumented impact strength measurements were made using an unnotched Charpy technique. The plastic yielding was then quantified with the use of a ductility ratio. The impact strengths and ductility of the reactive blends are found to be up to 73% greater than those of the corresponding non-reactive blends. Increasing the OPS concentration beyond 5% results in decreasing impact strength, for as the compatibility increases, the rubber particle size decreases below an effective size for rubber toughening. Similar impact improvement is observed when the major PS phase is substituted with high impact polystyrene (HIPS) containing some OPS.     

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.     

PS／PP反应性共混研究

本文研究了ＲＰＳ（含恶唑啉侧基苯乙烯）和ＭＰＰ的反应性共混以及ＲＰＳ－ＭＰＰ作为ＰＳ／ＰＰ相容剂的效果，考察了ＲＰＳ与ＭＰＰ比例、剪切作用大小对共混物性能的影响并从ＳＥＭ观察ＰＳ／ＰＰ共混物相态结构及其冲击强度测定的结果表明，ＲＰＳ－ＭＰＰ是ＰＳ／ＰＰ体系较好的相容剂。     

聚丙烯接枝衣康酸增容PA6／PP共混物性能及形态研究

采用反应型双螺杆挤出机和熔融接枝技术制备了一系列聚丙烯（PP）接枝物，包括单一单体接枝物PP接枝衣康酸（PP-g-ITA）和双单体接枝物PP接枝ITA和苯乙烯[PP-g-（ITA-co-St）]，通过红外光谱和热分析研究了PP接枝物的结构，并研究了PP接枝物的接枝率和熔体流动速率与单体和引发剂用量的关系。通过反应挤出制备了PP接枝物增容PA6／PP共混物，研究了增容共混物的力学性能和形态结构。结果显示：加入接枝物后，共混体系的冲击强度明显提高；SEM观察表明，接枝物的加入能明显改善增容共混物的两相界面结合状况，降低共混物的分散相尺寸，改善体系的分散状况，共混物的两相界面变得模糊，相容性得到明显提高；DSC测试表明，加入接枝物后，共混物中PA6组分的结晶度下降，PP组合的结晶度上升。表明PP-g-ITA是PA6／PP共混体系有效的增容剂兼增韧剂。     

Tough polyamide 6/core–shell blends prepared via in situ anionic polymerization of ε‐caprolactam by reactive extrusion

In this study, the molten ε‐caprolactam (CL) solution of maleated styrene‐ethylene/butylene‐styrene block copolymer (SEBS‐g‐MA) and polystyrene (PS) containing catalyst and activator were introduced into a twin screw extruder, and polyamide 6 (PA6)/SEBS/PS blends were successfully prepared via anionic polymerization of CL by reactive extrusion. The mechanical properties measurements indicated that both the elongation at break and notched Izod impact strength of PA6/SEBS/PS (85/10/5) blends were improved distinctly with slight loss of tensile and flexural strength as compared to that of pure PA6. The images of transmission electron microscopy showed that a core–shell structure with PS core and poly (ethene‐co‐1‐butene) (PEB) shell was formed within the PA6 matrix. Fourier transform infrared was used to investigate the formation mechanisms of the core–shell structure. POLYM. ENG. SCI., 53:2705–2710, 2013. © 2013 Society of Plastics Engineers     

Evaluation and characterization of vector fluids and peroxides in a process of in situ compatibilization of polyethylene and polystyrene

An organic functional silane was found to be the most efficient among several vector fluids in reactive blend compatibilization of the polyethylene (PE) / polystyrene (PS) / peroxide / vector fluid system. This paper involves further analysis of this reactive blending system. Surface tension data was used to calculate spreading coefficients which were compared to the amount of PE-PS copolymer formed during blending. A good correlation between a computed spreading coefficient and the degree of grafting of PS onto PE was found. The results suggest that the pattern of distribution of the vector fluid in PE / PS blends is the key factor leading to effective results. Furthermore, different peroxides were evaluated in PE / PS blends, in order to determine the dependence of PE / PS interfacial grafting reaction on the structure of the peroxide.     

Sub-micron dispersed-phase particle size in polymer blends: overcoming the Taylor limit via solid-state shear pulverization

A comparison was made of the fineness of dispersion in immiscible polymer blends achieved by a continuous mechanical alloying technique, solid-state shear pulverization, relative to that achieved by melt mixing. Two polymer blend systems were investigated. A polystyrene (PS)/polyethylene (PE) wax blend was studied because, based on a classic analysis by G.I. Taylor, melt mixing was expected to yield a number-average dispersed-phase domain size, D_n, well above 1 μm. A PS/high density polyethylene (HDPE) blend was also studied because it was known to produce a sub-micron number-average dispersed-phase particle size when mixed by twin-screw extrusion. In the case of the PS/PE wax blend at compositions ranging from 1 to 15 wt% polyethylene wax, pulverization resulted in nearly identical D_n values (typical value of 0.7 μm) independent of minor-phase content; these D_n values were an order of magnitude smaller than the anticipated Taylor limit for melt-mixed blends. In contrast, PS/PE wax blends made by batch, intensive melt mixing yielded D_n values between ∼3 μm at both 1 and 5 wt% minor-phase content and 17.5 μm at 15 wt% minor-phase content. The increase in D_n with increasing dispersed-phase content in the melt-mixed blend is a consequence of coalescence present during melt processing; such effects are disallowed in the pulverization process occurring in the solid state. Scanning electron microscopy of a 95/5 wt% PS/HDPE blend provided D_n values of 500 and 270 nm in the twin-screw extruded and pulverized samples, respectively. Fractionated crystallization studies further corroborated the ability of pulverization to result in a finer, nanoscopic dispersion of the minor phase as compared to extrusion.     

Rheology, morphology and tensile properties of reactive compatibilized polyethylene/polystyrene blends via Friedel–Crafts alkylation reaction

Attempts were made to study the effect of reactive compatibilization via Friedel?CCrafts alkylation reaction, using AlCl₃ as a catalyst, on rheology, morphology, and mechanical properties of polyethylene/polystyrene (PE/PS) blends. The results of linear viscoelastic measurements in conjunction with the results of the mixing torque variation indicated that PS showed much more degradation than that of PE in the presence of AlCl₃. It was also found that while for PE-rich blends, the viscosity, and storage modulus increased by reactive compatibilization, they decreased for PS-rich blends. The variation of viscosity and storage modulus for 50/50 blend was found to be dependent on frequency ranges showing the competitive effects of PE?Cg?CPS copolymer formation and PS degradation. The results of morphological studies showed that reactive compatibilization decreased the particle size and particle-size distribution broadness because of in situ graft copolymer formation. Reactive compatibilization enhanced the tensile strength and elongation at break for PE-rich blends. It was demonstrated that there is a close interrelationship between rheology, morphology, and mechanical properties of reactive compatiblized PE/PS blends. It was also demonstrated that rheological behaviors have a reliable sensitivity to follow the structural and morphological changes during compatibilization process, so that, those information can be used to predict the morphology as well as mechanical properties of the blends.     

Toughness enhancement of polylactide with low amounts of poly (butylene adipate-co-terephthalate) through in situ reactive compatibilization

Polylactide (PLA) was melt blended with low amounts of poly (butylene adipate-co-terephthalate) (PBAT) using a simple reactive extrusion process herein, aiming to address the inherent brittleness of PLA without significantly compromising its stiffness. PLA/PBAT (90/10) blends with a small amount of peroxide (0.02 phr) and a second crosslinker agent triallyl isocyanurate (TAIC) were produced to explore the structure-performance relationship evolution in reactive extrusion. The results showed that the PLA blend with an appropriate amount of TAIC (i.e., 0.3 phr) exhibited a remarkable increase in elongation at break, reaching as high as 96%. The sample with high elongation also demonstrated a high stiffness, boasting a Young's modulus of 2.4 GPa and a yield strength of 43 MPa. It was evident that the combination of enhanced compatibility and optimized homogeneous PBAT phase size of approximately 0.6 μm worked synergistically to enhance the toughness of PLA. Conversely, higher TAIC contents resulted in over-crosslinking, despite considerable improvements in compatibility. This study offers a versatile, scalable, and practical method to prepare fully biodegradable PLA blends with high toughness.     

Preparation and characterization of high melt strength polypropylene with long chain branched structure by the reactive extrusion process

The reactive extrusion of maleic anhydride grafted polypropylene (PP‐g‐MAH) with ethylenediamine (EDA) as coupling agent is carried out in a corotating twin‐screw extruder to produce long chain branched polypropylene (LCBPP). Part of PP‐g‐MAH is replaced by maleic anhydride grafted high‐density polyethylene (HDPE‐g‐MAH) or linear low‐density polyethylene (LLDPE‐g‐MAH) to obtain hybrid long chain branched (LCB) polyolefins. Compared with the PP‐g‐MAH, PE‐g‐MAH, and their blends, the LCB polyolefins exhibit excellent dynamic shear and transient extensional rheological characteristics such as increased dynamic modulus, higher low‐frequency complex viscosity, broader relaxation spectra, significantly enhanced melt strength and strain‐hardening behaviors. The LCB polyolefins also have higher tensile strength, tensile modulus, impact strength and lower elongation at break than their blends. Furthermore, supercritical carbon dioxide (scCO₂) is constructively introduced in the reactive extrusion process. In the presence of scCO₂, the motor current of the twin extruder is decreased and LCB polyolefins with lower melt flow rate (MFR), higher complex viscosity and increased tensile strength and modulus can be obtained. This indicates that the application of scCO₂ can reduce the viscosity of melt in extruder, enhance the diffusion of reactive species, and then facilitate the long chain branching reaction between anhydride group and primary amine group. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of the anhydride terminated polycarbonate and its reactive compatibilization with polystyrene

Polycarbonate with anhydride end groups (PC‐anh) was prepared by the reaction between polycarbonate having hydroxyl end groups (PC‐OH) and trimellitic anhydride chloride (TMAC). Hydroxyl or anhydride terminated polycarbonates were characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. The reaction of PC‐anh with polystyrene containing oxazoline reactive groups (RPS) was confirmed not only by the torque measurement during melt blending of these two but also by FTIR spectroscopy of the reactive blend obtained. Polycarbonate (PC) / polystyrene (PS) compatibilized blends were prepared by melt blending along with their reactive counterparts, PC‐anh and RPS in the Haake mixer. The morphologies of these blends were examined by the scanning electron microscope (SEM). The compatibilized blends with reactive components showed relatively finer morphologies than the uncompatibilized blend without reactive components. Izod impact strength and rheological property of these blends were also investigated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1338–1347, 2000     

Rheological and mechanical properties of compatibilized polystyrene/ethylene vinyl acetate blends

In this study, a blend of polystyrene (PS)/ethylene vinyl acetate (EVA) (PS/EVA, 90 : 10 wt %) was compatibilized with three different block copolymers, in which their end blocks were compatible with either styrene or EVA. The compatibilized blends with different compositions were prepared using a twin‐screw extruder and injection molded into the required test specimens. Mechanical properties of the blends, such as tensile properties and Charpy impact strength, morphology of tensile fractured surfaces, rheological properties, and thermal properties, were investigated. The results show that the interaction between the dispersed and continuous phase can be improved by the addition of a compatibilizer. Appreciable improvement in the impact strength of the blend with 15 wt % of compatibilizer C (polystyrene‐block‐polybutadiene) was observed. Its mechanical properties are comparable to those of the commercial high‐impact polystyrene, STYRON 470. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2071–2082, 2004     

Compatibilization of polystyrene and low density polyethylene blends by a two-step crosslinking process

A new method has been developed to compatibilize the blends of polystyrene (PS) and polyethylene (PE). Polyethylene is first crosslinked partially by using a small amount of dicumyl peroxide (DCP) in a mixer at 165°C. Then the crosslinked PE is melt-blended with PS for another 5 min. Finally, a styrene–butadiene–styrene block copolymer (SBS) is added to the melt and mixed for another 5 min. We refer to this special procedure as the two-step crosslinking process. During the final mixing step of this process, the residual free radicals in the PE react with SBS. The crosslinking that occurs between PE and SBS has a significant impact on the mechanical properties of the blends including the impact strength, the tensile modulus, and the elongation-at-break. Scanning electron microscopy (SEM) results indicate that the interfacial adhesion is increased significantly, even though the domain sizes have not changed significantly in comparison with the non-crosslinked system. Transmission electron microscopy (TEM) results indicate that a thin SBS interfacial layer fully encapsulates the PE particles. This method could also be applied to other blend systems containing at least one component and a compatibilizer that are crosslinkable.     

Recycling of high density polyethylene/poly(vinyl chloride)/polystyrene ternary mixture with the aid of high energy radiation and compatibilizers

Ternary mixtures of waste plastics of high density polyethylene (HDPE), poly(vinyl chloride) (PVC), and polystyrene (PS) was recycled using a single‐screw extruder. Poly(ethylene‐co‐vinyl acetate) and poly(styrene‐b‐ethylene/butylenes‐b‐styrene) were introduced as compatibilizers for HDPE/PVC and HDPE/PS, respectively. After the polymer blends was prepared via extrusion, they were subjected to high energy irradiation. The morphology and the mechanical properties of the hybrid blends were examined. Scanning electron micrographs and transmission electron micrographs showed that both compatibilizers and irradiation improved the uniformity and dispersion of the system. The heterogeneous crosslinking generated by irradiation resulted in an optimum impact strength. High elongation at break was achieved by using compatibilizers. The improvement of tensile strength was moderate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 12: 2756–2762, 2003     

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     

Influences of dicumyl peroxide on morphology and mechanical properties of polypropylene/poly(styrene‐b‐butadiene‐b‐styrene) blends via vane‐extruder

Polypropylene (PP) and poly(styrene‐b‐butadiene‐b‐styrene) block copolymer (SBS) were melt‐blended in the presence of initiator system. Dicumyl peroxide (DCP)/Triallyl isocyanurate (TAIC) via self‐deigned VE, aiming at in situ reactive compatibilization of toughed PP/SBS blend. The reactivity, morphology and mechanical properties of PP/SBS/DCP/TAIC blends were studied. Online torque detection was conducted to monitor changes in viscosities of reactive compatibilized blends, which could give proof of the interfacial grafted reaction induced by DCP/TAIC system. The effect of reactive compatibilization on the dispersed particles sizes and interfacial adhesion was studied by scanning electron microscopy. Analysis on mechanical performance revealed the impact strength improved after treated by initiator system, moreover, the impact‐fractured surface observation showed, the failure mode changed from debonding mechanism of neat 50PP/50SBS blend to plastic deformation mechanism of blend containing 3.0 phr initiator system. With improved interfacial adhesion, compatibilized blends not only were toughened but also exhibited enhanced tensile strength and thermal stability. Dynamic mechanical analysis showed a reduction of between PP phase and the PB segments in SBS phase, indicating reactive compatibilization of the blend was achieved. In the final part, a brief discussion was given about the dominant effects from chain scission of PP matrix to intergrafting reactions of PP and SBS, under different content of DCP/TAIC initiator system. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41543.     

Formation of phase structure and crystallization behavior in blends containing polystyrene–polyethylene block copolymers

The microphase separation structure in the molten state and the structure formation in crystallization from such ordered melt were investigated for the blends of polystyrene–polyethylene block copolymers (SE) with polystyrene homopolymer (PS) and polyethylene homopolymer (PE) and for the blends consisting of two kinds of SE with different copolymer compositions from each other, using synchrotron small-angle X-ray scattering techniques (SAXS). The copolymer compositions of SE block copolymers employed were 0.34, 0.58 and 0.73 wt. fraction of PE, and their melt morphologies were cylindrical, lamellar and lamellar, respectively. Macrophase separation or the morphology change in the melt occurred depending on the molecular weight and the blend composition, as reported so far. In crystallization from such macrophase-separated and microphase-separated melts, the melt morphology was completely kept for all the blends. Crystallization behavior was also investigated for the blends. The crystallization within the spherical and cylindrical domains surrounded by glassy PS was not observed for SE/PS blends. In the crystallization from the macrophase-separated melt, two exothermal peaks were observed in the DSC measurements, while a single peak was observed for other blends. For the blends with PS, the degree of crystallinity was depressed and the apparent activation energy of crystallization was high, compared to those for the corresponding neat SE. For SE/PE and SE/SE blends, those were changed depending on the blend composition.