Styrenic polymer nanocomposites based on an oligomerically-modified clay with high inorganic content

Clay was modified with an oligomeric surfactant containing styrene and lauryl acrylate units along with a small amount of vinylbenzyl chloride to permit the formation of an ammonium salt so that this can be attached to a clay. The oligomerically-modified clay contains 50% inorganic clay, and styrenic polymer nanocomposites, including those of polystyrene (PS), high-impact polystyrene (HIPS), styrene-acrylonitrile copolymer (SAN) and acrylonitrile-butadiene-styrene (ABS), were prepared by melt blending. The morphologies of the nanocomposites were evaluated by X-ray diffraction and transmission electron microscopy. Mixed intercalated/delaminated nanocomposites were formed for SAN and ABS while largely immiscible nanocomposites were formed for PS and HIPS. The thermal stability and fire properties were evaluated using thermogravimetric analysis and cone calorimetry, respectively. The plasticization from the oligomeric surfactant was suppressed and the tensile strength and Young's modulus were improved, compared to similar oligomerically-modified clays with higher organic content.     

Preparation of microcellular polypropylene/polystyrene blend foams with tunable cell structure

By using supercritical carbon dioxide (sc‐CO₂) as the physical foaming agent, microcellular foaming was carried out in a batch process from a wide range of immiscible polypropylene/polystyrene (PP/PS) blends with 10–70 wt% PS. The blends were prepared via melt processing in a twin‐screw extruder. The cell structure, cell size, and cell density of foamed PP/PS blends were investigated and explained by combining the blend phase morphology and morphological parameters with the foaming principle. It was demonstrated that all PP/PS blends exhibit much dramatically improved foamability than the PP, and significantly decreased cell size and obviously increased cell density than the PS. Moreover, the cell structure can be tunable via changing the blend composition. Foamed PP/PS blends with up to 30 wt% PS exhibit a closed‐cell structure. Among them, foamed PP/PS 90:10 and 80:20 blends have very small mean cell diameter (0.4 and 0.7 µm) and high cell density (8.3 × 10¹¹ and 6.4 × 10¹¹ cells/cm³). Both of blends exhibit nonuniform cell structure, in which most of small cells spread as “a string of beads.” Foamed PP/PS 70:30 blend shows the most uniform cell structure. Increase in the PS content to 50 wt% and especially 70 wt% transforms it to an irregular open‐cell structure. The cell structure of foamed PP/PS blends is strongly related to the blend phase morphology and the solubility of CO₂ in PP more than that in PS, which makes the PP serve as a CO₂ reservoir. Copyright © 2009 John Wiley & Sons, Ltd.     

应用超临界CO2制备微孔聚丙烯的微孔形貌

研究了应用超临界CO2技术制备微孔聚丙烯时发泡条件和聚丙烯(PP)的熔体强度对微孔形貌的影响。结果表明:在一定的饱和压力下,随着温度的升高,PP的变形能力改善,有利于泡孔的长大。随着饱和压力的增加,PP的熔点降低,升高压力和升高温度具有一定的等同作用。由于CO2在PP内分散的不同,高压低温时得到的泡孔比高温低压时得到的泡孔要规整。降压速率对泡孔形貌的影响因饱和压力的大小而异,饱和压力较高时随着降压速率的提高,孔密度增加,泡孔形貌经历了一个从球体到多面体转变的过程。由于PP熔体强度较低,在发泡温度和PP熔点之间非常接近时,CO2气体容易冲破孔壁而使泡孔呈开孔结构。     

Effect of ionizing radiation on physicochemical and mechanical properties of commercial monolayer and multilayer semirigid plastics packaging materials

Tensile testing, overall migration tests and sensory tests were used to evaluate the effects of gamma irradiation (5–60 kGy) on six commercial semirigid packaging materials. The monolayer and multilayer materials in sheet or bottle form were: polystyrene (PS), polypropylene (PP), polyvinyl chloride/high-density polyethylene (PVC/HDPE), polyethylene terepthalate (PET), HDPE/polyamide (HDPE/PA) and HDPE. In terms of mechanical strength, PET was the most radiation-resistant material, while the HDPE monolayer and multilayer showed some degradation after 60 kGy. PS was slightly affected after 30 kGy, whereas PP was severly degraded and became very brittle. Generally, there was no change in overall migration at lower doses; at higher doses migration from PP tended to increase, while migration from HDPE/PVC tended to decrease. Odor and taste transfer as well as discoloration were observed with most plastics, especially at higher doses, and it is concluded that these tests are a sensitive and important quality control tool for evaluating irradiated packaging materials.     

Degradation of pre-aged polymers exposed to simulated recycling: Properties and thermal stability

Accelerated thermal and photo-aging of four homopolymers, low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP) and high-impact polystyrene (HIPS), was performed and the impact of subsequent reprocessing conditions on their properties studied. Polymer samples oven-aged at 100 °C for varying periods of time or UV irradiated in a Weather-o-meter (WOM) at λ = 340 nm were reprocessed in a Brabender plasticorder at 190 °C/60 rpm for 10 min. Chemical changes and the evolution of rheological and mechanical properties accompanying the gradual degradation of the individual polymers were monitored and evaluated (DSC, FTIR, colorimetric method, MFI, tensile impact strength). LDPE and HIPS were found to be more susceptible to thermo-oxidation than HDPE and PP, whereas HDPE and PP were affected to a greater extent by UV exposure; the crucial role here is being played by the stabilization of the studied resins. In HDPE the scission and crosslinking reactions competed both in thermo-and photo-degradation. In the case of LDPE, scission prevailed over branching during thermo-oxidation, whereas photo-oxidation of the same sample led predominantly to crosslinking. Abrupt deterioration of the LDPE rheological properties after one week of thermal exposure was suppressed by re-stabilization. The scission reaction was also predominant for PP during thermo-oxidation, and it took place even faster during UV exposure. In the case of HIPS a slight photo-degradation of PS matrix is accompanied by simultaneous crosslinking of the polybutadiene component.     

Benzimidazolium surfactants for modification of clays for use with styrenic polymers

Nanocomposites of polystyrene (PS), acrylonitrile-butadiene-styrene copolymer (ABS) and high impact polystyrene (HIPS) were prepared with two new homologous benzimidazolium surfactants used as organic modifications for the clays. The morphology of the polymer/clay hybrids was evaluated by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM), showing good overall dispersion of the clay. The thermal stability of the polymer/clay nanocomposites was enhanced, as evaluated by thermogravimetric analysis. From cone calorimetric measurements, the peak heat release rate of the nanocomposites was decreased by about the same amount as seen for other organically-modified, commercially available clays.     

Photodegradation of polypropylene/polystyrene blends: Styrene-butadiene-styrene compatibilisation effect

The mutual influence between the PP/PS polymer blend components during UV photodegradation was studied. Polypropylene (PP) and polystyrene (PS) have different photodegradation mechanisms, due to the larger UV absorption of polystyrene and formation of more stable tertiary carbon radicals. To compare the stabilities the kinetics of carbonyl formation was measured in different blend compositions. The results show that polystyrene presented a faster carbonyl formation than polypropylene, while the blends display faster kinetics than the isolated components. The kinetics of carbonyl formation of the blends was a function of polypropylene content. This result is unexpected if one considers the behaviour of each component alone. The kinetics and mechanism of UV degradation can be only explained taking into account the interaction between the blend components. PS absorbs UV light and energy is transferred to PP, which produces more reactive tertiary carbon free radicals. The effect of the interaction between the domains is enhanced when a compatibiliser is used, corroborating the hypothesis of energy transfer.     

焦煤与不同种类废塑料共焦化的研究

采用10g常压固定床反应器、热天平和偏光显微镜,对太钢炼焦煤中添加不同种类废塑料（如HDPE,LDPE,PP和PS）后热解的产品分布、半焦的光学特性以及热重行为进行了研究。结果表明：煤和塑料的热解温度范围和峰温的差异决定二者协同作用的程度;四种塑料的添加对净焦煤的半焦收率无明显影响;当添加HDPE、LDPE、PP时,焦煤的焦油收率增加,热解水收率下降,但添加PS时的情况正相反;除了PP外,添加其它各类的塑料能增加半焦中的光学各向异性组织的含量。     

Styrenic nanocomposites prepared using a novel biphenyl-containing modified clay

Montmorillonite was organically modified using an ammonium salt containing 4-acetylbiphenyl. This clay (BPNC16 clay) was used to prepare polystyrene (PS), acrylonitrile butadiene styrene (ABS) and high impact polystyrene (HIPS) nanocomposites. Polystyrene nanocomposites were prepared both by in situ bulk polymerisation and melt blending processes, while the ABS and HIPS nanocomposites were prepared only by melt blending. X-ray diffraction and transmission electron microscopy were used to confirm nanocomposite formation. Thermogravimetric analysis was used to evaluate thermal stability and the flammability properties were evaluated using cone calorimetry. By thermogravimetry, BPNC16 clay was found to show high thermal stability, and by cone calorimetry, a decrease in both the peak heat release rate and the mass loss rate was observed for the nanocomposites.     

THE CHEMICAL MODIFICATION OF POLYVINYL CHLORIDE

Abstract

Poly (vinyl chloride) (PVC) is commercially one of the most important thermoplastics in the world today. Its growth rate averaged 7% per annum in the 1970s. In 1980 it was the second largest volume thermoplastic used in the United States (the first being low-density polyethylene (LDPE) and was the lowest priced among the five leading plastics: LDPE, PVC, high-density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS).     

Novel Thermoplastic Composites from Commodity Polymers and Man-Made Cellulose Fibers

Summary: A new class of fibre reinforced commodity thermoplastics suited for injection moulding and direct processing applications has been developed using man-made cellulosic fibres (Rayon tire yarn, Tencel, Viscose, Carbacell) and thermoplastic commodity polymers, such as polypropylene (PP), polyethylene (PE), high impact polystyrene (HIPS), poly(lactic acid) (PLA), and a thermoplastic elastomer (TPE) as the matrix polymer. For compounding, a specially adapted double pultrusion technique has been employed which provides composites with homogeneously distributed fibres. Extensive investigations were performed with Rayon reinforced PP in view of applications in the automotive industry. The Rayon-PP composite is characterized by high strength and an excellent impact behaviour as compared with glass fibre reinforced PP, thus permitting applications in the field of engineering thermoplastics such as polycarbonate/acrylonitrile butadiene styrene blends (PC/ABS). With the PP based composites the influence of material parameters (e.g. fibre type and load, coupling agent) were studied and it has been demonstrated how to tailor the desired composite properties as modulus and heat distortion temperature (HDT) by varying the fibre type or adding inorganic fillers. Man-made cellulose fibers are also suitable for the reinforcement of further thermoplastic commodity polymers with appropriate processing temperatures. In case of PE modulus and strength are tripled compared to the neat resin while Charpy impact strength is increased five-fold. For HIPS mainly strength and stiffness are increased, while for TPE the property profile is changed completely. With Rayon reinforced PLA, a fully biogenic and biodegradable composite with excellent mechanical properties including highly improved impact strength is presented.     

超临界CO_2发泡法制备PLGA多孔组织工程支架

利用超临界CO2(SC-CO2)发泡法制备了一系列聚(乳酸-乙醇酸)共聚物(PLGA)多孔支架材料,研究了PLGA分子量和组成、发泡过程温度、压力以及泄压速率等对泡孔尺寸及形态的影响.结果表明,随着PLGA组成中乳酸含量的增加,泡孔平均孔径增大且连通性增强;提高过程压力易形成孔径小且泡孔密度大的微孔结构材料;降低泄压速率,泡孔易合并形成大孔.聚合物处于高弹态时,较低的发泡温度易导致特殊的多面体结构大孔的形成;而当温度较高时,泡孔塌缩形成球形微孔结构,且泡孔尺寸随着温度升高而增大.SC-CO2发泡法能有效地去除有机溶剂,避免在高温条件下操作,可以实现5～500μm范围内孔径可控的PLGA多孔支架材料的制备.     

Formation of nanocomposites of styrene and its copolymers using graphite as the nanomaterial

Graphite‐polymer nanocomposites were prepared by melt blending of various graphites (virgin graphite, expandable graphites, and expanded graphite) with polystyrene and its copolymers (acrylonitrile‐butadiene‐styrene (ABS) and high‐impact polystyrene (HIPS)). Nanocomposites were characterized by X‐ray diffraction, cone calorimetry, thermogravimetric analysis and evaluation of mechanical properties. Nanocomposite formation occurs at higher loadings (3–5%) of expandable graphites but not for virgin or expanded graphite. Copyright © 2005 John Wiley & Sons, Ltd.     

Vacuum Ultraviolet Photolysis of Polyethylene,Polypropylene, and Polystyrene

Using infrared reflection absorption spectroscopy (IRRAS), quartz crystal microbalance (QMB) measurements, and X-ray photoelectron spectroscopy (XPS) in combination with chemical derivatization techniques the VUV photolysis of polyethylene (PE), polypropylene (PP), and polystyrene (PS) was investigated. A mass balance obtained from the quantification of the data was used to suggest reaction path ways. Although PE and PP behave similar, the mass loss is about 8 times higher in the case of PP. These differences originate from the higher disproportionation to recombination ratio for the branched polymer. Both polymers form double bonds and at extended treatment times they tend to crosslink. PS is rather stable due to the possibility of the energy dissipation by fluorescence.     

Vacuum Ultraviolet Photolysis of Polyethylene,Polypropylene, and Polystyrene

Using infrared reflection absorption spectroscopy (IRRAS), quartz crystal microbalance (QMB) measurements, and X-ray photoelectron spectroscopy (XPS) in combination with chemical derivatization techniques the VUV photolysis of polyethylene (PE), polypropylene (PP), and polystyrene (PS) was investigated. A mass balance obtained from the quantification of the data was used to suggest reaction path ways. Although PE and PP behave similar, the mass loss is about 8 times higher in the case of PP. These differences originate from the higher disproportionation to recombination ratio for the branched polymer. Both polymers form double bonds and at extended treatment times they tend to crosslink. PS is rather stable due to the possibility of the energy dissipation by fluorescence.     

Modelling of the High-Impact Polystyrene Morphogenesis

Summary: High-impact polystyrene (HIPS) is a hetero-phase polymer with the so-called salami morphology. Salami morphology is formed by a continuous PS phase containing micron-sized PB domains. PB domains contain submicron-sized irregular PS occlusions. In our modeling work we addressed several weak points of Cahn-Hilliard model of HIPS salami morphology evolution. The weakest point of Cahn-Hilliard model is the inherently present Ostwald ripening destabilizing or competing with graft-stabilized domains. Two mechanism of formation of HIPS morphology are supported by the model: (i) encapsulation of graft-stabilized PS-rich domains in PB particles, and (ii) polymerization of styrene dissolved in PB-rich phase and subsequent phase separation leading to PS occlusions in PB domains.     

Effect of temperature and pressure on surface tension of polystyrene in supercritical carbon dioxide

The surface tension of polymers in a supercritical fluid is one of the most important physicochemical parameters in many engineering processes, such as microcellular foaming where the surface tension between a polymer melt and a fluid is a principal factor in determining cell nucleation and growth. This paper presents experimental results of the surface tension of polystyrene in supercritical carbon dioxide, together with theoretical calculations for a corresponding system. The surface tension is determined by Axisymmetric Drop Shape Analysis-Profile (ADSA-P), where a high pressure and temperature cell is designed and constructed to facilitate the formation of a pendent drop of polystyrene melt. Self-consistent field theory (SCFT) calculations are applied to simulate the surface tension of a corresponding system, and good qualitative agreement with experiment is obtained. The physical mechanisms for three main experimental trends are explained by using SCFT, and none of the explanations quantitatively depend on the configurational entropy of the polymer constituents. These calculations therefore rationalize the use of simple liquid models for the quantitative prediction of surface tensions of polymers. As pressure and temperature increase, the surface tension of polystyrene decreases. A linear relationship is found between surface tension and temperature, and between surface tension and pressure; the slope of surface tension change with temperature is dependent on pressure.     

HIPS／PP熔融反应共混及其动态力学性质

研究了高抗冲聚苯乙烯（HIPS）／聚丙烯（PP）共混物在过氧化二异丙苯（DCP）存在下的熔融反应过程及其动态力学性质．HIPS在DCP存在下以聚苯乙烯（PS）的降解为主，伴随着聚丁二烯（PB）的交联和接枝，PP在DCP存在下以降解为主，HIPS／PP在DCP存在下以PP同HIPS的反应接枝为主，这种原位生成的增容剂显著地改善了HIPS／PP两组份间的相容性，其分子运动特征较前两者发生明显变化，PS的Tg下降，PB和PP的Tg升高．     

Preparation and characterization of microcellular polystyrene/polystyrene ionomer blends with supercritical carbon dioxide

The preparation of microcellular polystyrene (PS), lightly sulfonated polystyrene (SPS), zinc‐neutralized lightly sulfonated polystyrene (ZnSPS), and blends of PS/SPS and PS/ZnSPS via supercritical CO₂ was carried out with the pressure‐quench process. Both higher foaming temperature and lower pressure result in larger cell sizes, lower cell densities, and lower relative density for microcellular ionomers and blends as for microcellular PS. The difference among various microcellular samples is the change of cell size with the sample composition. The cell size decreases in the sequence from SPS, through PS/SPS blends, PS and PS/ZnSPS blends, to ZnSPS. The diffusivity of CO₂ in samples also decreases in the sequence from SPS, through PS/SPS blends, PS and PS/ZnSPS blends, to ZnSPS. For this series of samples with similar structure and identical solubility of CO₂, the varying diffusivity is responsible for the difference of cell sizes. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 368–377, 2003     

Supercritical CO<Subscript>2</Subscript> assisted preparation of open-cell foams of linear low-density polyethylene and linear low-density polyethylene/carbon nanotube composites

The open-cell structure foams of linear low-density polyethylene (LLDPE) and linear low-density polyethylene (LLDPE)/multi-wall carbon nanotubes (MWCNTs) composites are prepared by using supercritical carbon dioxide (sc-CO₂) as a foaming agent. The effects of processing parameters (foaming temperature, saturation pressure, and depressurization rate) and the addition of MWCNTs on the evolution of cell opening are studied systematically. For LLDPE foaming, the foaming temperature and saturation pressure are two key factors for preparing open-cell foams. An increase in temperature and pressure promotes both the cell wall thinning and cell rupture, because a high temperature results in a decrease in the viscosity of the polymer, and a high pressure leads to a larger amount of cell nucleation. Moreover, for the given temperature and pressure, the high pressurization rate results in a high pressure gradient, favoring cell rupture. For LLDPE/MWCNTs foaming, the addition of MWCNTs not only promotes the cell heterogeneous nucleation, but also prevents the cell collapse during cell opening, which is critical to achieve the open-cell structures with small cell size and high cell density.