Effects of formulation and processing parameters on the morphology of extruded polypropylene‐(waste ground rubber tire powder) foams

This paper presents an experimental study of the foaming behavior of polypropylene (PP)/(waste ground rubber tire powder) (WGRT) blends when using a chemical blowing agent in an extrusion foaming process. The effects of formulations (i.e., WGRT content, blowing agent content, compatibilizer) and the processing parameters (i.e., die temperature, screw speed) on the void fraction, average cell size, cell density, and cell morphology of the PP/WGRT foams were investigated. The blowing agent loading affected the cell structure of the foams and the average cell size, and the void fraction increased with increasing blowing agent loading. Both increasing the screw speed and decreasing the die temperature could establish a high pressure drop in the extruder die, and these were beneficial to the foaming extrusion. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

PP/POE/WGRT热塑性弹性体的制备及性能研究

采用动态硫化法制备了PP/POE/WGRT共混型热塑性弹性体（TPE）,考察了PP/WGRT共混比、在PP相中填充POE以及动态硫化法对TPE力学性能的影响。结果表明,改变PP/WGRT共混比以及在PP相中填充POE均不能获得TPE;采用动态硫化法制备的PP/POE/WGRT TPE具有较好力学性能,且当DCP用量为3份时TPE力学性能最佳。FE-SEM观察结果表明,动态硫化法使得PP/POE/WGRT TPE的界面作用获得增强,力学性能获得改善。     

Influence of compatibilizers and processing temperature on microcellular injection‐molded polypropylene/(waste tire powder) composites

Nowadays the economic recycling of waste tires has become a global challenge. The use of waste tire powder as a dispersed elastomeric phase in a polypropylene (PP) matrix offers an interesting opportunity for recycling of waste tire rubber. Compatibilized PP/(waste tire powder) composites are microcellularly processed to create a new class of materials with unique properties. Recent studies have demonstrated the feasibility of developing microcellular structures in PP/waste ground rubber tire (WGRT) composites. Microcellular PP/WGRT composites are prepared by an injection‐molding process using a chemical blowing agent. In this study, cell sizes, cell density, void fraction, and mechanical properties of the composite foams were measured, as well as the shear viscosity of the unfoamed composites. The influence of various compatibilizers and processing temperatures on cell morphology and the mechanical properties of injection‐molded PP/WGRT composites were investigated. It was seen that the addition of maleic anhydride‐grafted styrene‐ethylene‐butylene‐styrene (SEBS‐g‐MA) increased the shear viscosity of the composites. The void fraction and cell density of the PP/WGRT composites increased with addition of compatibilizers, whereas the average cell sizes decreased. A processing temperature range of 180–195°C gave finer microcellular structure and regular cell distribution. The SEBS‐g‐MA enhanced the elongation properties and acted as an effective compatibilizer in this particular system. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Waste ground rubber tire powder/thermoplastic vulcanizate blends: Preparation,characterization, and compatibility

In this article, waste ground rubber tire (WGRT) powder was introduced into thermoplastic vulcanizate (TPV) to prepare the blends of WGRT powder/TPV. The mechanical, rheological, thermal aging, and dynamic properties of the blends were investigated with respect to the particle size and dosage of WGRT powder. The results showed that tensile strength, tear strength, elongation at break, and tensile permanent deformation of the blends increased with the decrease in WGRT particle size and decreased with the dosage of WGRT. The effects of different types and dosages of compatibilizers on mechanical and rheological properties of the blends were studied. The results showed that the compatibilizer PP‐g‐MAH could effectively improve the interfacial compatibility between WGRT and the TPV matrix to enhance the comprehensive properties of blends. The TPV/WGRT/PP‐g‐MAH blends obtained the best overall properties when prepared at the weight ratio 100/30/5. Rheological studies demonstrated that the WGRT/TPV blends represented lower apparent viscosity after PP‐g‐MAH were added, which means that processing performance of the blends was improved by PP‐g‐MAH. Scanning electron microscopy was used to study the morphologies of the blends. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39868.     

Foaming conditions of high density polyethylene–natural rubber blends

Abstract

Foams made from high density polyethylene (HDPE) and natural rubber (NR) blends, using azodicarbonamide as a chemical blowing agent, have been investigated to establish a relationship between the structure and physical properties. The blends of HDPE, NR, epolene wax, chemical blowing agent, and necessary ingredients were prepared on a two roll mill. Subsequently, foamed structures of the blends were obtained by a single stage compression moulding. Results indicate that foaming process variables, i.e. heating time, blowing agent loading, ratio of HDPE/NR, crosslinking agent loading, and ratio of HDPE/NR at a fixed crosslinking agent loading, affect the physical properties of the foams. Attempts were made to relate such properties as foam density, hardness, tensile strength, elongation at break, tear strength, flexural strength, elastic modulus, and gel content to the foam structure. The foam structure was investigated using optical microscopy, in terms of the average cell size and its distribution.     

Dynamic reaction involving surface modified waste ground rubber tire powder/polypropylene

The surface of waste ground rubber tire (WGRT) powder has been modified with by allylamine via an ultraviolet (UV) treatment. The degree of grafting of the modified‐WRGT are confirmed by the Fourier Transform Infrared spectroscopy (FTIR), scanning electron microscopy, energy dispersive X‐ray analysis, thermogravimetric analysis, and surface energy measurements. And then they incorporated into the polypropylene (PP) matrix. The effects of UV radiation time, WGRT loading, and allylamine concentration on the mechanical properties of the composites are measured. Mechanical properties are influenced as a function of UV radiation time, WGRT loading, and allylamine concentrations. The chemical interactions between grafted WGRT and PP matrix are investigated by X‐ray diffraction and FTIR. They show change of the crystallinity of the PP and the chemical reaction between WGRT and the PP. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers     

基于废旧轮胎胶粉的热塑性弹性体的制备及发泡性能研究

通过沥青改性胶粉及采用相容剂与聚丙烯共混制备了性能优良的热塑性弹性体(TPE)材料,并以超临界流体为发泡剂对其发泡性能进行了研究。实验结果表明,胶粉通过沥青改性后,可以明显地提高TPE的拉断伸长率,并且发泡TPE的泡孔平均直径增大,泡孔密度减少,相对密度减小,但是随着沥青用量的增加,材料的粘度降低,从而出现泡孔破裂和塌陷现象,最后导致泡孔平均直径和泡孔密度减小,相对密度增加。相容剂苯乙烯嵌段共聚物接枝马来酸酐(SEBS-g-MA)可以提TPE的拉断伸长率并改善泡孔结构。温度的升高和饱和压力的增大,都导致了发泡弹性体的泡孔增大,泡孔密度和相对密度减小。     

Mechanical and morphological properties of cellular NR/SBR vulcanizates under thermal and weathering ageing

The effects of addition of two chemical blowing agents in cellular rubber blend of natural rubber (NR) and styrene‐butadiene rubber (SBR) at a fixed blend ratio of 1 : 1 on cure characteristics, and mechanical and morphological properties were invesigated. The chemical blowing agents used in this work were Oxybis (benzene sulfonyl) hydrazide (OBSH) and Azo dicarbonamide (ADC). Three different fillers, fly ash (FA) particles, precipitated silica, carbon black (CB) at their optimum concentrations of 40 phr were used, the FA and silica particles being chemically treated by bis‐(3‐triethoxysilylpropyl) tetrasulphide. The results suggested that the overall cure time decreased with OBSH and ADC contents. The OBSH was more effective in cure‐acceleration of the NR/SBR blend than the ADC. The NR/SBR vulcanized foams produced by OBSH and ADC agents had closed‐cell structures. The specific density and mechanical properties of the blend tended to decrease with increasing blowing agent content. The CB gave NR/SBR foams with smaller cell size, better cell dispersion, and higher mechanical properties than the precipitated silica and FA particles. The heat ageing and weathering resulted in an increase in tensile modulus and hardness, but lowered the tensile strength, ultimate elongation and tear strength. The elastic recovery for cellular NR/SBR vulcanizates with FA was superior to that with CB and silica, the elastic recovery of the blends decreasing with blowing agent content. Resilience property was improved by the presence of gas phases. The optimum concentration of OBSH and ADC to be used for NR/SBR vulcanizates was 4 phr. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Study on the effect of dispersion phase morphology on porous structure of poly (lactic acid)/poly (ethylene terephthalate glycol-modified) blending foams

A methodology for blending foam of poly (lactic acid) (PLA)/poly (ethylene terephthalate glycol-modified) (PETG) was proposed. PLA/PETG blends were prepared through a melt blending method, using multiple functionality epoxide as reactive compatibilizer. The effects of blending ratio and compatibilizer content on the dispersion morphology, molecular structure, mechanical properties, and rheological behavior of PLA/PETG blends were studied. Then PLA/PETG blends were foamed using supercritical CO₂ as physical blowing agent, and their porous structure, pore size, as well as pore density were investigated. The results showed that the mechanical properties and rheological parameters such as melt strength and melt elasticity, as well as the porous structure of the foams dispersion morphology of PLA/PETG blends were affected strongly. The melt elasticity of PLA/PETG blends increased with increasing compatibilizer content. Dispersion phase morphology of PLA/PETG blends also had a significant effect on the pore density of all the samples. The results indicated that homogeneous and finer porous morphology of PLA/PETG foams with high expansion ratio could be achieved with a proper content of compatibilizer in the blends.     

Batch Foam Processing of Polypropylene/Polydimethylsiloxane Blends

Batch foaming processes were employed to prepare plastic foams from polypropylene (PP)/polydimethylsiloxane (PDMS) blends. Various amounts of PDMS were added to a PP matrix, and the resulting blends were batch foamed at different saturation pressures using carbon dioxide (CO₂) as the blowing agent. Ultimately, the blend foams exhibited better cell morphologies and higher cell densities in comparison with those prepared from PP alone. The increased solubility of CO₂ in PDMS made it as a CO₂ reservoir to induce more nucleation. When the PDMS content exceeded a certain level, however, it exerted a negative influence on cell density. Moreover, as the saturation pressure was raised, the cell density of the blend foams increased significantly. It was also noted that the addition of PDMS to the PP matrix generated some very small cells in the larger cell walls.     

Dynamic reaction inside co‐rotating twin screw extruder. II. Waste ground rubber tire powder/polypropylene blends

In this article, dynamic reaction of waste ground rubber tire powder/PP blends with compatibilizers is extended to commercially available waste rubber Viz. Ground rubber tire and PP for the possibility of getting recycled material with good mechanical properties. In the first part of the article it was shown that the compatibility of model material/PP blends has greatly improved. In this article, extensive studies have been carried out to study the effect of compatibilizers, in‐situ compatibilization of immiscible waste ground rubber tire (WGRT) powder/polyolefin blends of various concentrations was investigated by means of extrusion process using a co‐rotating twin screw extruder. It was observed that addition of small amounts of compatibilizers like SEBS‐g‐MA to the blends of WGRT and PP‐g‐MA can result in better mechanical properties than the blends with isotactic PP. The blends of WGRT powder and PP‐g‐MA with compatibilizer have better adhesion than those of isotactic PP blends as revealed by the morphological studies using AFM and SEM. The betterment in properties can be attributed to the presence of functional group, maleic anhydride in PP‐g‐MA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation and morphology of polypropylene/wood flour composite foams via extrusion

In this study, polypropylene (PP)/wood flour composites foams with an average cell size lower than 100 μ were successfully produced by extrusion. The effects of the coupling agent (maleated PP), wood flour content (20%, 30%, and 40% weight), initial wood moisture, and blowing agent content on the cell structure are reported. It was found that the addition of a coupling agent increases the blowing agent efficiency and helps to reduce the density of the composites. Moreover, wood moisture appears to be an effective secondary blowing agent under specific conditions. POLYM. COMPOS., 26:731–738, 2005. © 2005 Society of Plastics Engineers     

Relationship between cell morphology and impact strength of microcellular foamed high‐density polyethylene/polypropylene blends

Polymer blends, such as those resulting from recycling postconsumer plastics, often have poor mechanical properties. Microcellular foams have been shown to have the potential to improve properties, and permit higher‐value uses of mixed polymer streams. In this study, the effects of microcellular batch processing conditions (foaming time and temperature) and HDPE/PP blend compositions on the cell morphology (the average cell size and cell‐population density) and impact strength were studied. Optical microscopy was used to investigate the miscibility and crystalline morphology of the HDPE/PP blends. Pure HDPE and PP did not foam well at any processing conditions. Blending facilitated the formation of microcellular structures in polyolefins because of the poorly bonded interfaces of immiscible HDPE/PP blends, which favored cell nucleation. The experimental results indicated that well‐developed microcellular structures are produced in HDPE/PP blends at ratios of 50:50 and 30:70. The cell morphology had a strong relationship with the impact strength of foamed samples. Improvement in impact strength was associated with well‐developed microcellular morphology. Polym. Eng. Sci. 44:1551–1560, 2004. © 2004 Society of Plastics Engineers.     

Effects of the blending sequence and interfacial agent on the morphology and mechanical properties of injection molded PC/PP Blends

Summary The effects of blending sequence and the addition of an interfacial agent (triblock copolymer styrene-butylene ethylene/styrene, Kraton G1652) on the morphology and the mechanical properties of Polycarbonate (PC)/Polypropylene (PP) blends prepared by injection molding were studied. This study presents an analysis of impact resistance, tensile properties and morphology of the raw materials and the blends at different compositions. The blends, before being injected, were prepared in a twin-screw extruder by different sequences of blending. The results indicate that the blending sequence and the presence of humidity significantly affect the properties and morphology of the blends. For ternary blends (PC/PP/Kraton), only one-step mixing before injection molding proved to be sufficient to improve mechanical properties. Increasing the amount of blending steps did not present a significant change in properties. With the addition of the interfacial agent, higher impact resistance and particle size reduction were observed.     

Extruded foams from microbial poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) and its blends with cellulose acetate butyrate

Extrusion foaming of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) and two blends of PHBV with cellulose acetate butyrate (CAB) were studied using an azodicarbonamide (AZ) blowing agent and a single‐screw extruder. The concentration of the blowing agent was systematically varied from 0 to 4.0 phr to achieve maximum density reduction reaching 41%, as well as to obtain information on the dependence of cell growth on blowing agent concentration. Extruded foams were characterized in terms of their bulk densities and cellular morphologies. Stereological and statistical methods permitted full characterization of the three‐dimensional cell size distributions, assessing the average cell diameters (ranging from 58 to 290 μm) and cell densities (ranging from 650 to 180,000 cm^?3). The variation in cellular morphology among foams consisting of different polymer matrix or blowing agent concentration was compared. The results were analyzed by considering the influence of viscoelastic properties of the polymer matrix on the bubble growth during foaming. Significantly higher melt viscosity and elasticity and reduced gas solubility of the PHBV/CAB blends are believed to retard cell coalescence and collapse during foam expansion, resulting in more uniform cell size distribution and better homogeneity of cellular morphology. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Effect of the introduction of polydimethylsiloxane on the foaming behavior of block‐copolymerized polypropylene

We investigated the effect of polydimethylsiloxane (PDMS) on the foaming properties of block‐copolymerized polypropylene (B‐PP) by blending different contents of PDMS with B‐PP in the extrusion process using supercritical CO₂ as the blowing agent. The experimental results indicate that the addition of PDMS greatly increased the expansion ratio of the foamed samples. At the same time, the cell population density of foams obtained from the blends also increased to a certain degree and provided a new perspective on improving B‐PP's foaming performance. The addition of PDMS also decreased the die pressure because of the reduced viscosity of the B‐PP/PDMS blends compared with that of the B‐PP matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Improving polypropylene microcellular foaming through blending and the addition of nano‐calcium carbonate

This article reports an attempt to improve polypropylene (PP) microcellular foaming through the blending of PP with high‐density polyethylene (HDPE) as a minor component and the incorporation of nano‐calcium carbonate (nano‐CaCO₃) into PP and its blends with HDPE. Three HDPEs were selected to form three blends with a viscosity ratio less than, close to, or greater than unity. Two concentrations of nano‐CaCO₃, 5 and 20 wt %, were used. The blends and nanocomposites were prepared with a twin‐screw extruder. The foaming was carried out by a batch process with supercritical carbon dioxide as a blowing agent. The online shear viscosity during compounding and the dynamic rheological properties of some samples used for foaming were measured. The cell structure of the foams was examined with scanning electron microscopy (SEM), and the morphological parameters of some foams were calculated from SEM micrographs. The rheological properties of samples were used to explain the resulting cell structure. The results showed that the blend with a viscosity ratio close to unity produced a microcellular foam with the minimum mean cell diameter (0.7 μm) and maximum cell density (1.17 × 10¹¹ cells/cm³) among the three blends. A foamed PP/nano‐CaCO₃ composite with 5 wt % nano‐CaCO₃ exhibited the largest cell density (8.4 × 10¹¹ cells/cm³). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Structure and properties of closed‐cell foam prepared from irradiation crosslinked silicone rubber

Silicone rubber foam was prepared through crosslinking with electron beam irradiation and foaming by the decomposing of blowing agent azobisformamide (AC) in hot air. The crosslinking and foaming of silicone rubber was carried out separately, which was different from the conventional method of chemical crosslinking and foaming. After foaming, the silicone rubber foam was irradiated again to stabilize the foam structure and further improve its mechanical properties. The effects of irradiation dose before and after foaming, and the amount of blowing agents on the structure and properties of silicone rubber foam were studied. The experimental results show that with the increase of AC content, the average cell diameter of silicone rubber foam increases a little, the foam density decreases to a minimum value when AC content is 10 phr. With the increase of irradiation dose before foaming from 10 to 17.5 kGy, the cell nucleation density of silicone rubber foam increases, the average cell diameter decreases, and the foam density increases. With the increase of irradiation before foaming, the tensile strength, tensile modulus, and the elongation at break of the silicone rubber foam increase. Through irradiation crosslinking again after foaming, the foam density is decreased and the mechanical properties of silicone foam are further improved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The development of laminar morphology during extrusion of polymer blends

Studies of the microstructure and permeability of extruded ribbons of polypropylene (PP)/ethylene vinyl alcohol copolymer (EVOH) and polyethylene (PE)/polyamide-6 (PA-6) blends have shown that it is possible to control the flow-induced morphology to generate discontinuous overlapping platelets of EVOH or PA-6 dispersed phase in a PP or HDPE matrix phase. The effects of the following factors on morphology development and blend properties were considered: blending sequence, melt temperature, composition, compatibilizer level, die design, screw type, and cooling conditions. The impact properties and interfacial adhesion of laminar blends of PP and EVOH were improved without diminishing the barrier properties. The oxygen and toluene permeability of extruded samples with EVOH content of 25 vol% resembled values obtained with multilayer systems. Processing conditions had a major influence on the morphology of blends of high density polyethylene and polyamide-6 (HDPE/PA-6), and, under special processing conditions, laminar morphology was obtained in this system. The toluene permeability of extruded ribbons of HDPE/PA-6 blends was in the range obtained with multilayer systems.     

Extrusion Foaming of Poly (lactic acid)/Soy Protein Concentrate Blends

Poly(lactic acid) (PLA) and soy protein concentrate (SPC) were compounded using poly(2‐ethyl‐2‐oxazoline) as compatibilizer by twin‐screw extrusion, and the resulting blends were foamed by a chemical blowing agent (CBA) using the same extruder. Effects of foaming temperature and CBA content on cell density and foam density were investigated. Polymeric methylene diphenyl diisocyanate (pMDI) as a co‐compatibilizer was added prior to foaming extrusion and its effects on foam morphology and properties were also studied. The results showed that cell density and foam density were greatly influenced by foaming temperature and CBA content. Using the strong interfacial modifier pMDI in PLA/SPC blends resulted in high‐cell density and low‐foam density when CBA concentration was low.