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Polypropylene
Kinds of Polypropylene Terms modified by Polypropylene Selected AbstractsEqual Cosmetic Outcomes with 5-0 Poliglecaprone-25 Versus 6-0 Polypropylene for Superficial ClosuresDERMATOLOGIC SURGERY, Issue 7 2010LAURA B. ROSENZWEIG MD BACKGROUND Cutaneous sutures should provide an aesthetically pleasing result. After placing subcutaneous sutures, enough absorbable suture often remains for the superficial closure. Mohs surgeons often use a nonabsorbable suture to close the superficial layer to obtain cosmetically elegant results, but using this additional suture is less cost effective than using the remaining absorbable suture. OBJECTIVES To compare the cosmetic results of simple running sutures using an absorbable suture material (5-0 poliglecaprone-25) with those of a nonabsorbable suture (6-0 polypropylene) in primary closures of suitable facial Mohs defects. MATERIALS AND METHODS Fifty-two patients with 57 facial Mohs surgery defects appropriate for multilayer primary repair had the defects prospectively randomized into a side-by-side comparison. After closure of the deep layers with 5-0 poliglecaprone-25 sutures, half of the wound was closed with a 5-0 poliglecaprone-25 simple running suture, and the other half of the wound was closed with a 6-0 polypropylene simple running suture. The investigators blindly determined the cosmetically superior side of the closure at 1 week and 4 months after suture removal. RESULTS Forty-four patients (48 total defects) completed the study. At the 4-month follow-up, 85% (41/48) did not show any difference between poliglecaprone-25 and polypropylene, 4% (2/48) had better outcomes with poliglecaprone-25, and 10% (5/48) had better outcomes with polypropylene. There was no statistically significant cosmetic difference between the two closure types. Wound complications such as infection, hematoma, and dehiscence did not occur in any of the patients. CONCLUSION In primary closures of facial defects, using 5-0 poliglecaprone-25 or 6-0 polypropylene for the superficial closure did not affect the cosmetic result. Therefore, 5-0 poliglecaprone-25 provides a comparable and cost-effective alternative to nonabsorbable sutures for epidermal approximation in layered closures. The authors have indicated no significant interest with commercial supporters. [source] Heat Transfer in Polypropylene-Based Foams Produced Using Different Foaming Processes,ADVANCED ENGINEERING MATERIALS, Issue 10 2009Marcelo Antunes This paper presents the characterization of the cellular structure and thermal conduction behaviour of polypropylene foams produced using different foaming processes, with the aim of selecting the best possible PP foam thermal insulator. Thermal conductivity results have shown that the global heat transfer behaviour is controlled by the relative density. For relative densities higher than 0.2, thermal conductivity differences were insignificant, the data being predicted by the mixture's rule and Russell's model. In the low density range, all of the proposed models underestimated the overall conductivity, the effect of the processing method being more significant, slight differences being observed between foams produced by extrusion and those produced by gas dissolution with higher cell sizes and anisotropies. Foams with finer cellular structures showed to be better insulating materials. [source] Stereoblock Polypropylene as a Prototype Example of Elasticity via a Flip-Flop Reorientation of Crystals in a Compliant Matrix,ADVANCED MATERIALS, Issue 6 2007F. Auriemma Elastomeric polypropylene characterized by chains with an isotactic and atactic stereoblock structure shows elastic behavior in a large range of deformations notwithstanding the high degree of crystallinity, because of the occurrence of flip-flop reversible reorientation of crystals of the , form that occur during stretching and the successive release of tension, as shown schematically in the figure. [source] "Chain-End-Controlled Isotactic" and "Stereoblock-Isotactic" Polypropylene: Where Is the Difference?ISRAEL JOURNAL OF CHEMISTRY, Issue 4 2002Vincenzo Busico This communication describes the microstructure of "stereoblock-isotactic" polypropylene obtained with sterically hindered "oscillating" metallocene catalysts, points out in which respects it differs from that of "chain-end-controlled isotactic" polypropylene, and explains why the two definitions cannot be used as synonymous (as is commonly found in the literature). [source] Rotational foam molding of polypropylene with control of melt strengthADVANCES IN POLYMER TECHNOLOGY, Issue 4 2003Remon Pop-Iliev Abstract Polypropylene (PP) has not been used extensively in rotational foam molding because it has been traditionally considered as nonfavorable for foaming applications because of its relatively weak melt strength and melt elasticity at elevated temperatures. However, because of the unique end-use properties of PP, PP foams have recently grown in importance. An experimental study was conducted to identify feasible processing strategies for producing PP foams with satisfactory morphologies in dry-blending-based rotational foam molding. The obtained results revealed that cell coalescence plays a key role in the production of PP foams in rotational foam molding. If it is efficiently suppressed, the cell morphology of the PP foams improves dramatically. To suppress cell coalescence, it would be necessary to preserve the melt strength of PP during processing. One way of doing this is maintaining the temperature of the PP melt as low as possible. This can be accomplished by either lowering the decomposition temperature of the chemical blowing agent by using an activator such as zinc oxide and/or reducing the temperature of the oven. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 280,296, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10056 [source] Prediction of cooling time in injection molding by means of a simplified semianalytical equationADVANCES IN POLYMER TECHNOLOGY, Issue 3 2003D. M. Zarkadas Abstract A simplified semianalytical equation, used successfully in food freezing/chilling time prediction, is proposed as a potential simple alternative for cooling time prediction in injection molding of polymer parts, amorphous or semicrystalline. This equation is based on a convective boundary condition for the mold-part interface and requires information on the thermal contact resistance (TCR) or thermal contact conductance (TCC) at this interface, as well as information on the initial and final product temperatures, the mold surface temperature, and the thermal properties of the part. Eighty-five data points for four polymers, Polystyrene (PS), Polycarbonate (PC), Polypropylene (PP), and Polyethylene (PE) were generated with C-MOLDÔ, a commercial injection molding design software, and the performance of the proposed equation was tested. The % mean error and its standard deviation (SD) in cooling time prediction were, respectively, ,11.61 and 2.27 for PS, ,6.04 and 2.13 for PC, ,7.27 and 6.55 for PP, and ,8.88 and 2.93 for PE. It was also shown that the accuracy of the proposed equation is not affected significantly by the exact knowledge of the TCC, provided that the latter is not smaller than 1000,2000 W m,2 K,1. Since in this comparison all necessary temperatures were obtained from C-MOLDÔ, methods of using the proposed equation independently were tested. The use of the inlet melt temperature as the initial product temperature increased the % mean error by mostly 1.5% while its SD remained practically the same. By incorporating a literature based heat balance method in the proposed equation, it was possible to use it as a stand-alone predictor of polymer cooling time. The % mean error and its SD calculated this way were, respectively, ,9.44 and 0.97 for PS, ,9.44 and 0.83 for PC, ,14.22 and 5 for PP, and ,20.12 and 1.38 for PE. The proposed equation, at least in a preliminary stage, can be used successfully to predict the cooling time of the selected semicrystalline or amorphous polymers with the accuracy being higher for amorphous polymers. © 2003 Wiley Periodicals, Inc. Adv Polym Techn 22: 188,208, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10048 [source] Comparison of volatile emissions and structural changes of melt reprocessed polypropylene resinsADVANCES IN POLYMER TECHNOLOGY, Issue 4 2002Q. Xiang Abstract Polypropylene (PP), as a commodity recyclable thermoplastic, was studied in this research to evaluate the potential environmental impact resulting from volatile organic compounds (VOCs) emitted during multiple melt reprocessing. Unstabilized PP (U-PP) and stabilized PP (S-PP) resins, simulating recycled materials prone to degradation, were evaluated for total VOC emissions generated during multiple melt reprocessing by injection molding and extrusion, respectively. Results show that the maximum amount of total VOCs from each cycle (up to six cycles for extrusion and up to ten for injection molding) did not significantly change, while the cumulative VOCs increased with increasing processing cycle for both materials. A good correlation between cumulative VOC increases and melt flow index increase for the U-PP and weight-average molecular weight Mw decrease for the S-PP were obtained. Reprocessing in all cases was accompanied by decreases in Mw and melt viscosity as a result of thermooxidative degradation. FTIR data considering increases in carbonyl content and degree of unsaturation suggest that at equivalent cycle numbers, degradation appears to be more severe for the extruded material in spite of the longer oxidative induction time of the "as received" pellets used in extrusion. The onset and type of structural changes are shown to depend on cycle number and reprocessing method. © 2002 Wiley Periodicals, Inc. Adv Polym Techn 21: 235,242, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.10027 [source] Flammability and mechanical properties of wood flour-filled polypropylene compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010M. B. Abu Bakar Abstract Polypropylene (PP) composites filled with wood flour (WF) were prepared with a twin-screw extruder and an injection-molding machine. Three types of ecologically friendly flame retardants (FRs) based on ammonium polyphosphate were used to improve the FR properties of the composites. The flame retardancy of the PP/WF composites was characterized with thermogravimetric analysis (TGA), vertical burn testing (UL94-V), and limiting oxygen index (LOI) measurements. The TGA data showed that all three types of FRs could enhance the thermal stability of the PP/WF/FR systems at high temperatures and effectively increase the char residue formation. The FRs could effectively reduce the flammability of the PP/WF/FR composites by achieving V-0 UL94-V classification. The increased LOI also showed that the flammability of the PP/WF/FR composites was reduced with the addition of FRs. The mechanical property study revealed that, with the incorporation of FRs, the tensile strength and flexural strength were decreased, but the tensile and flexural moduli were increased in all cases. The presence of maleic anhydride grafted polypropylene (MAPP) resulted in an improvement of the filler,matrix bonding between the WF/intumescent FR and PP, and this consequently enhanced the overall mechanical properties of the composites. Morphological studies carried out with scanning electron microscopy revealed clear evidence that the adhesion at the interfacial region was enhanced with the addition of MAPP to the PP/WF/FR composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Effects of rice husk (RH) particle size, glass fiber (GF) length, RH/GF ratio, and addition of coupling agent on the mechanical and physical properties of polypropylene-RH-GF hybrid compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010H. D. Rozman Abstract Polypropylene (PP) hybrid composites based on rice husk (RH) with different particle size and glass fiber (GF) with different length were prepared. The composites were subjected to mechanical and water immersion tests. From the results obtained, it was found that the mechanical properties of the hybrid composites were strongly dependent on the size of RH particle and length of GF. It could be further enhanced with the presence of coupling agent. In this study, two types of coupling agents, i.e., Epolene E-43 (E-43) and 3-(trimethoxysilyl)-propylmethacrylate (TPM), were employed. In general, E-43 imparted significant improvement in the mechanical properties. From the water immersion results, it was found that the hydrophobicity of the composites was increased with the presence of coupling agent. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Polypropylene nanocomposite film: A critical evaluation on the effect of nanoclay on the mechanical, thermal, and morphological behaviorJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010S. K. Sharma Abstract Polypropylene (PP)/clay nanocomposites prepared by melt blending technique using different percentages of clay with and without maleic anhydride grafted PP (MA-PP) were studied. The intercalated and exfoliated structure of nanocomposites was characterized by X-Ray Diffraction (XRD) and transmission electron microscopy (TEM). Because of the typical intercalated and exfoliated structure, the tensile modulus of the nanocomposites were improved significantly as compared to virgin PP. The viscoelastic behavior of the nanocomposites was studied by dynamical mechanical analysis (DMA) and the results showed that with the addition of treated clay to PP there was substantial improvement in storage modulus increases. The thermal stability and crystallization of the PP nanocomposites as studied by differential scanning calorimeter (DSC) and thermo gravimetric analysis (TGA) were also improved significantly compared to PP. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Accelerated ageing of polypropylene stabilized by phenolic antioxidants under high oxygen pressureJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Emmanuel Richaud Abstract Polypropylene (PP) samples stabilized by a hindered phenol (Irganox 1010) were submitted to thermal ageing at 80°C in air at atmospheric pressure or in pure oxygen at 5.0 MPa pressure. Both the polymer oxidation and the stabilizer consumption were monitored by Infrared spectrometry and thermal analysis. The stabilizer efficiency, as assessed by the ratio induction time/stabilizer concentration is almost constant at atmospheric pressure even when the stabilizer concentration is higher than its solubility limit in PP (0.4% or 24 × 10,3 mol L,1). In contrast, at high pressure, the efficiency decreases almost hyperbolically with the stabilizer concentration when this latter is higher than 6.0 × 10,3 mol L,1. The results indicate the existence of a direct phenol-oxygen reaction negligible at low oxygen pressure but significant at 5.0 MPa pressure. The reality of this reaction has been proved on the basis of a study of the thermal oxidation of a phenol solution in a nonoxidizable solvent. A kinetic model of PP oxidation in which stabilization involves three reactions has been proposed. It simulates correctly the effect of oxygen pressure and stabilizer concentration on carbonyl build-up and stabilizer consumption. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Polypropylene/clay nanocomposites prepared by in situ grafting-melt intercalation with a novel cointercalating monomerJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Pingan Song Abstract Polypropylene (PP)/clay nanocomposites were prepared by melt-compounding PP with organomontmorillonite (OMT), using maleic anhydride grafted polypropylene (PP- g -MA) as the primary compatibilizer and N -imidazol- O -(bicyclo pentaerythritol phosphate)- O -(ethyl methacrylate) phosphate (PEBI) as the cointercalating monomer. X-ray diffraction patterns indicated that the larger interlayer spacing of OMT in PP was obtained due to the cointercalation monomer having a large steric volume and the d -spacing further increased with the addition of PP- g -MA, as evidenced by transmission electron microscopy. Thermogravimetric analysis revealed that the PEBI-containing PP nanocomposites exhibited better thermal stability than PEBI-free PP composites. Dynamic mechanical analysis demonstrated that the storage modulus was significantly enhanced, and the glass transition temperature (Tg) shifted slightly to low temperature with the incorporation of clay for PP/OMT hybrids. PEBI-containing PP/OMT composites gave a lower Tg value because of the strong internal plasticization effect of PEBI in the system. Cone calorimetry showed that the flame-retardancy properties of PP nanocomposites were highly improved with the incorporation of PEBI. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Modeling of coat-hanger die under vibrational extrusionJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008Jin-Ping Qu Abstract The distributions of the pulsatile pressure field, the pulsatile velocity field, and the pulsatile resident time of the polymeric melt in the coat-hanger die are derived by using the pulsation of volumetric flow rate and pressure. Subsequently, formulae of the manifold radius and the slope of the manifold are deduced via volumetric flow rate pulsation. Polypropylene (PP) was employed for the experiments of the vibrational extrusion. The results indicate that the average extrusion pressure declines with frequency or amplitude decreasing; the distribution of residence time along the width of the coat-hanger die performs uniformly during the vibrational extrusion process; the theoretical extrusion pressure well agrees with the experimental pressure; the experiments of tensile test, impact test implicate that vibration improves the mechanical properties of products; differential scanning calorimetry testing demonstrates that the melting point of PP is moved to a higher temperature value, and the endothermic enthalpy and the crystallinity are improved as well when superimposing the vibrational force field. Accordingly, the model of the coat-hanger die under vibrational extrusion is well consistent with the experiments. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Polymer nanocomposites based on needle-like sepiolite clays: Effect of functionalized polymers on the dispersion of nanofiller, crystallinity, and mechanical propertiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2008E. Bilotti Abstract Polypropylene (PP)/sepiolite (Sep) nanocomposites are prepared by melt compounding in a mini-extruder apparatus. The often used maleic anhydride-modified polypropylene (PP-g-MA) is compared with two custom-made functionalized polymers, PP-acid and the di-block copolymer PP-PEO, with respect to the filler dispersion and filler reinforcement efficiency. For that purpose, morphological and mechanical studies are carried out by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), and mechanical tensile tests. In addition, the nanocomposites are characterized by wide-angle X-ray scattering (WAXS) and differential scanning calorimetric (DSC) techniques, to assess the effect of the nanofiller on the crystalline structure of the PP matrix nano-filler. The use of PP-PEO and PP-acid resulted in a better nanofiller dispersion compared with traditional PP-g-MA-modified systems. Sepiolite acts as nucleating agent for the crystallization of PP and seems to lead to an orientation of the ,-phase crystals. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source] Mechanical, flow, and morphological properties of talc- and kaolin-filled polypropylene hybrid compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007M. B. Abu Bakar Abstract Polypropylene (PP) hybrid composites have been produced by compounding two types of mineral fillers, viz., talc and kaolin with PP copolymer using a twin screw extruder. The PP hybrid composite was injection-molded into dumbbell specimen for tensile, flexural, and impact properties characterizations. MFI and SEM studies were used to characterize the flow and morphological properties of the PP hybrid composites. The result shows that most of the hybrid composites showed a significant decrease in flow, tensile, flexural, and impact properties compared with the single filler-filled PP composites. However, a hybridization effect was seen for the PPT20K10 hybrid composites, through the synergistic coalescence of positive characteristics from 20 wt % of talc and 10 wt % of kaolin. This hybrid formulation have given an economically advantageous material with the mechanical properties (tensile, flexural, and impact) comparable to those of the talc-filled PP composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 434,441, 2007 [source] Fabrication and properties of nano-ZnO/glass-fiber-reinforced polypropylene compositesJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 3 2010Yi-Hua Cui Polypropylene (PP) is widely used in many fields, such as automobiles, medical devices, office equipment, pipe, and architecture. However, its high brittle transformation temperature, low mechanical strength, dyeing properties, antistatic properties, and poor impact resistance, considerably limit its further applications. Nano-ZnO treated by KH550 coupling agent and glass fibers (GFs) were introduced in order to improve the mechanical performance and flowability of PP in this research. The crystallization behavior and microstructure of nano-ZnO/GFs/PP hybrid composites were analyzed by differential scanning calorimetry, transmission electron microscopy, and scanning electron microscopy. The effect of crystallization behavior on the mechanical properties of the nanocomposites was investigated and analyzed. The results indicated that nano-ZnO surface-coupled by KH550 could be uniformly dispersed in the PP matrix. The incorporation of nano-ZnO and GFs resulted in increases of the crystallization temperature and crystallization rate of PP and a decrease of the crystallization degree. The introduction of nano-ZnO and GFs also enhanced the tensile strength and impact toughness of the hybrid composites and improved their fluidity. Composites containing 2% of nano-ZnO and 40% of GFs possessed the optimum mechanical properties. J. VINYL ADDIT. TECHNOL., 2010. © 2010 Society of Plastics Engineers [source] Processing, Morphology, and Mechanical Properties of Liquid Pool Polypropylene with Different Molecular WeightsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2005Claudia Stern Abstract Summary: The processability, morphology, and resulting mechanical properties of novel polypropylene (PP) samples of varying molecular weight () were studied. A series of homopolymer PP in a wide range from 101,000 to 1,600,000 g,·,mol,1 was polymerised in a liquid pool (LP) under defined conditions. The LP-PP with a well-known polymerisation history was manufactured into micro dumbbell specimens by means of a micro injection-moulding process. The morphology and mechanical properties of the samples were studied by light microscopy, transmission and scanning electron microscopy, and a quasi-static tensile test. Simulation of the filling behaviour of the molten polymer inside the mould shows that the shear rate increases as the molecular weight increases, up to a maximum shear rate of 750,000 s,1. In addition, the present crystallisation time of the high-molecular-weight PP samples is clearly lower than their retardation time; the long macromolecules do not have sufficient time to retard while cooling. As a result of the shear-induced crystallisation, a highly oriented crystalline structure is formed as a function of the acting shear rate. SEM and TEM investigations show the existence of an oriented shish kebab structure. The density of the shish kebab increases as the molecular weight increases. Evaluations of the shear rate and the morphological structure indicate a critical shear rate of about 300,000 s,1. Above this shear rate level, shish kebab structures are favourably formed. The shear-induced crystallisation and, therefore, the preferred formation of a highly oriented shish kebab structure lead, obviously, to unusual solid-state properties of the analysed LP-PP samples. With a tensile strength up to 100 N,·,mm,2 and an attainable strain at break of more than 30%, the mechanical performance is much higher than results ever reported in literature. True strain,stress behaviour of moulded the LP-PP samples of different molecular weight. [source] Temperature and strain rate dependences of yield stress of polypropylene composites reinforced with carbon nanofibersPOLYMER COMPOSITES, Issue 12 2009S.P. Bao Polypropylene (PP) nanocomposites filled with 0.1, 0.3, 0.5, and 1.0 wt% carbon nanofiber (CNF) were prepared via melt compounding in a twin-screw extruder followed by injection molding. The effects of CNF additions on the structure, mechanical and tensile yielding behavior of PP were investigated. TEM and SEM observations showed that CNFs were dispersed uniformly within PP matrix. Tensile test showed that the yield strength and Young's modulus of PP were improved considerably by adding very low CNF loadings. The reinforcing effect of CNF was also verified from the dynamic mechanical analysis. Impact measurement revealed that the CNF additions were beneficial to enhance the impact toughness of PP. The yield stress of the PP/CNF nanocomposites was found to be strain rate and temperature dependent. The yielding responses of PP/CNF nanocomposites can be described successfully by the Erying's equation and a reinforcing index n. The structure and mechanical property relationship of the nanocomposites is discussed. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] Extrusion conditions and properties of vapor grown carbon fiber reinforced polypropylenePOLYMER COMPOSITES, Issue 5 2001Rex J. Kuriger Vapor grown carbon fiber (VGCF) is a new and inexpensive carbon fiber produced by vapor deposition of hydrocarbons on metal catalysts. The ability to fabricate VGCF reinforced thermoplastic composites by extrusion provides the potential to exploit VGCF into new commercial markets. This study investigates the extrusion conditions and properties of VGCF reinforced polypropylene. Extrusion was carried out using a Leistritz twin-screw extruder. Polypropylene reinforced with 0% to 12.5% volume fraction VGCF was extruded successfully at temperatures ranging from 215°C to 250°C. The extrusion pressure increased and the flow rate decreased as the percentage of fiber was increased. Increases in tensile strength and modulus were observed by the addition of VGCF. However, the void content of the composite samples increased with fiber content. [source] Swirl mat, and long discontinuous fiber mat,reinforced polypropylene composites,status and future trendsPOLYMER COMPOSITES, Issue 4 2000J. Karger-Kocsis Polypropylene (PP) composites with glass and natural fiber mat reinforcement (GMT-PP and NMT-PP, respectively) are widely used in different applications, competing with metallic sheets and thermoset polymer composites. Their production occurs via melt impregnation, slurry deposition and various textile architecturing processes that lead to either consolidated or non-consolidated preforms. These preforms are then converted into final parts by hot pressing. The "traditional" GMT-PP composites are nowadays faced with a great challenge because of the introduction of long fiber reinforced thermoplastic (LFT) composites produced on- or off-line. This paper gives a brief survey on the manufacturing, processing, properties and application of GMT and GMT-like systems and it concludes by describing some of the future trends, especially in the fields of material and process developments. [source] Gamma-irradiation effects on polypropylene-based composites with and without an internal lubricantPOLYMER ENGINEERING & SCIENCE, Issue 5 2009Witold Brostow Polypropylene (PP) based materials for nonreusable syringe applications have been investigated, some of them containing an internal liquid lubricant. Hardness, tensile properties, and friction measured by two distinct procedures have been determined. We report three series of results: for nonirradiated samples; for samples directly after stopping the irradiation; and also for samples after accelerated aging equivalent to 2 years of shelf life. We find that effects of irradiation and aging on Shore A and Shore D hardness are small. Tensile strength at break, elongation at yield, and elongation at break all decrease after irradiation and then decrease still more after aging; these results are quantified but expected. By contrast, results from pin-on-disk tribometry are quite varied. In some cases , irradiation and aging both increase friction, in other cases both decrease friction. We also have a case when irradiation increases friction while aging decreases it,as well as vice versa. Possible mechanisms of all these types of behavior are advanced. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] Polypropylene/Clay nanocomposites: Effect of compatibilizer on the thermal, crystallization and dynamic mechanical behaviorPOLYMER ENGINEERING & SCIENCE, Issue 9 2002Sangeeta Hambir Polypropylene (PP)/clay nanocomposites are prepared using different grades of PP, compatibilizers, and organically modified clays. The melt intercalation of the PP is carried out in presence of a compatibilizer. The nanocomposites are characterized using various techniques for the structure and properties. X-ray diffraction results indicate well-defined structures. Thermogravimetric analysis indicates improved thermal stability of PP/clay nanocomposites. Isothermal crystallization studies carried out using differential scanning calorimeter illustrate enhanced crystallization of PP in all the nanocomposites. Optical microscopic study demonstrates that the nanocomposites can be crystallized at higher temperatures, exhibiting well-defined birefringent structures. The dynamic mechanical analysis reveals higher storage moduli over a temperature range of ,400C to 1200C for nanocomposites, and the extent of increase in the storage modulus is dependent on the type of compatibilizer used. [source] Effect of the type of nylon chain-end on the compatibilization of PP/PP-GMA/nylon 6 blendsPOLYMER INTERNATIONAL, Issue 2 2002Adriana Tedesco Abstract Polyamide and polypropylene (PP) are two important classes of commercial polymers; however, their direct mixing leads to incompatible blends with poor properties. Polypropylene functionalized with glycidyl methacrylate (PP-GMA) was used as a compatibilizer in blends of PP and nylon 6, because of the possible reaction of NH2 and COOH groups with the epoxide group of GMA. Two types of nylon 6 with different ratios between NH2 and COOH groups were used. The one with higher concentration of COOH groups was less compatible with PP in a binary blend. When PP-GMA was used as a compatibilizer, a better dispersion of nylon in the PP matrix was obtained together with better mechanical properties for both nylons used in this work. © 2001 Society of Chemical Industry [source] Mechanical properties and thermal analysis of low-density polyethylene,+,polypropylene blends with dialkyl peroxidePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 4 2010Kamil, irin Abstract Polypropylene,+,low density polyethylene (PP,+,LDPE) blends involving 0, 25, 50, 75 and 100,wt% of PP with dialkyl peroxide (DAP) were prepared by melt blending in a single-screw extruder. The effects of adding dialkyl peroxide on mechanical and thermal properties of PP,+,LDPE blends have been studied. It was found that at lower concentrations of peroxide (e.g., 0,0.08,wt% of dialkyl peroxide) LDPE component is cross-linked and Polypropylene (PP) is degraded in all compositions of PP,+,LDPE blends. Mechanical properties (Tensile strength at break, at yield and elongation at break), Melt flow index (MFI), hardness, Scanning Electron Microscope (SEM) and thermal analyses (DSC) of these blends were examined. Because of serious degradation or cross-linking the mechanical properties and the crystallinty (%) of those products were decreased as a result of increasing peroxide content. Copyright © 2009 John Wiley & Sons, Ltd. [source] Properties of uniaxially stretched polypropylene filmsTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 6 2008Farhad Sadeghi Abstract Polypropylene (PP) films have been prepared through two different cast extrusion processes: one using a machine direction orientation (MDO) unit and the other stretching the films at the die under high cooling conditions (lab unit). Films for two PP resins different in molecular structure have been prepared using both processing techniques. The effect of the resin structure and the processing conditions on the film properties has been examined. It was found that the MDO unit generated a highly oriented fibrillar crystalline structure with a distribution of elongated thick fibrils while extrusion under high cooling conditions generated an oriented row nucleated lamellar structure. The films showed distinctive tensile responses in stretching, with a strong solid-elastic response for the oriented MDO films and a steady strain hardening after yielding for the sample obtained from lab unit cast extrusion. It was found that the strength in the transverse direction (TD) was particularly very low for the oriented MDO films made of the bimodal PP. The oxygen permeability was reduced with increasing draw ratio (DR) for the MDO films. The haze property for the MDO samples reduced to a plateau for DR up to 5 while clarity improved continuously with DR. Des films de polypropylène ont été préparés dans deux procédés d'extrusion différents: l'un utilise une unité MDO (orientation dans la direction de la machine) et l'autre l'étirement des films à la filière dans des conditions de refroidissement intense (unité de laboratoire). Des films de polypropylène (PP) venant de deux résines de structure moléculaire différente ont été préparés à l'aide de ces deux techniques de mise en forme. L'effet de la structure de la résine et des conditions de mise en ,uvre sur les propriétés des films a été examiné. On a trouvé que l'unité MDO donne une structure cristalline fibrillaire hautement orientée avec une distribution de fibrilles épaisses allongées, tandis que l'extrusion sous refroidissement intense donne une structure lamellaire nucléée orientée en rangée. Les films montrent des réponses en contraintes à l'étirement distinctes, avec une forte réponse élastique solide pour les films MDO orientés et un écrouissage stable après déformation irréversible pour l'échantillon obtenu par extrusion avec l'unité de laboratoire. On a trouvé que la tenacité dans la direction transverse était particulièrement faible pour les films MDO orientés faits de PP bimodal. La perméabilité à l'oxygène a été réduite avec l'augmentation du rapport d'étirage pour les films MDO. La propriété de perte de transparence légère pour les échantillons MDO montre un plateau pour un rapport d'étirage allant jusqu'à 5 tandis que la clarté s'améliore continuellement avec le rapport d'étirage. [source] Oil Spill Cleanup from Sea Water by Sorbent MaterialsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2005A. Bayat Abstract Three sorbents were compared in order to determine their potential for oil spill cleanup. Polypropylene nonwoven web, rice hull, and bagasse with two different particle sizes were evaluated in terms of oil sorption capacities and oil recovery efficiencies. Polypropylene can sorb almost 7 to 9 times its weight from different oils. Bagasse, 18 to 45 mesh size, follows polypropylene as the second sorbent in oil spill cleanup. Bagasse, 14 to 18 mesh size, and rice hull have comparable oil sorption capacities, which are lower than those of the two former sorbents. It was found that oil viscosity plays an important role in oil sorption by sorbents. All adsorbents used in this work could remove the oil from the surface of the water preferentially. [source] The Combined Catalytic Action of Solid Acids with Nickel for the Transformation of Polypropylene into Carbon Nanotubes by PyrolysisCHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2007Rongjun Song Abstract The effects of both organically modified montmorillonite (OMMT) and Ni2O3 on the carbonization of polypropylene (PP) during pyrolysis were investigated. The results from TEM and Raman spectroscopy showed that the carbonized products of PP were mainly multiwalled carbon nanotubes (MWNTs). Surprisingly, a combination of OMMT and Ni2O3 led to high-yield formation of MWNTs. X-ray powder diffraction (XRD) and GC,MS were used to investigate the mechanism of this combination for the high-yield formation of MWNTs from PP. Brønsted acid sites were created in degraded OMMT layers by thermal decomposition of the modifiers. The resultant carbenium ions play an important role in the carbonization of PP and the formation of MWNTs. The degradation of PP was induced by the presence of carbenium ions to form predominantly products with lower carbon numbers that could be easily catalyzed by the nickel catalyst for the growth of MWNTs. Furthermore, carbenium ions are active intermediates that promote the growth of MWNTs from the degradation products with higher carbon numbers through hydride-transfer reactions. The XRD measurements showed that Ni2O3 was reduced into metallic nickel (Ni) in situ to afford the active sites for the growth of MWNTs. [source] Equal Cosmetic Outcomes with 5-0 Poliglecaprone-25 Versus 6-0 Polypropylene for Superficial ClosuresDERMATOLOGIC SURGERY, Issue 7 2010LAURA B. ROSENZWEIG MD BACKGROUND Cutaneous sutures should provide an aesthetically pleasing result. After placing subcutaneous sutures, enough absorbable suture often remains for the superficial closure. Mohs surgeons often use a nonabsorbable suture to close the superficial layer to obtain cosmetically elegant results, but using this additional suture is less cost effective than using the remaining absorbable suture. OBJECTIVES To compare the cosmetic results of simple running sutures using an absorbable suture material (5-0 poliglecaprone-25) with those of a nonabsorbable suture (6-0 polypropylene) in primary closures of suitable facial Mohs defects. MATERIALS AND METHODS Fifty-two patients with 57 facial Mohs surgery defects appropriate for multilayer primary repair had the defects prospectively randomized into a side-by-side comparison. After closure of the deep layers with 5-0 poliglecaprone-25 sutures, half of the wound was closed with a 5-0 poliglecaprone-25 simple running suture, and the other half of the wound was closed with a 6-0 polypropylene simple running suture. The investigators blindly determined the cosmetically superior side of the closure at 1 week and 4 months after suture removal. RESULTS Forty-four patients (48 total defects) completed the study. At the 4-month follow-up, 85% (41/48) did not show any difference between poliglecaprone-25 and polypropylene, 4% (2/48) had better outcomes with poliglecaprone-25, and 10% (5/48) had better outcomes with polypropylene. There was no statistically significant cosmetic difference between the two closure types. Wound complications such as infection, hematoma, and dehiscence did not occur in any of the patients. CONCLUSION In primary closures of facial defects, using 5-0 poliglecaprone-25 or 6-0 polypropylene for the superficial closure did not affect the cosmetic result. Therefore, 5-0 poliglecaprone-25 provides a comparable and cost-effective alternative to nonabsorbable sutures for epidermal approximation in layered closures. The authors have indicated no significant interest with commercial supporters. [source] Frequency of Use of Suturing and Repair Techniques Preferred by Dermatologic SurgeonsDERMATOLOGIC SURGERY, Issue 5 2006BETH ADAMS MD BACKGROUND There are many closure techniques and suture types available to cutaneous surgeons. Evidence-based data are not available regarding the frequency of use of these techniques by experienced practitioners. OBJECTIVE To quantify, by anatomic site, the frequency of use of common closure techniques and suture types by cutaneous surgeons. METHOD A prospective survey of the members of the Association of Academic Dermatologic Surgeons that used length-calibrated visual-analog scales to elicit the frequency of use of specific suture techniques. RESULTS A response rate of 60% (61/101) indicated reliability of the received data. Epidermal layers were closed most often, in descending order, by simple interrupted sutures (38,50%), simple running sutures (37,42%), and vertical mattress sutures (3,8%), with subcuticular sutures used more often on the trunk and extremities (28%). The most commonly used superficial sutures were nylon (51%) and polypropylene (44%), and the most common absorbable suture was polyglactin 910 (73%). Bilayered closures, undermining, and electrocoagulation were used, on average, in 90% or more sutured repairs. The median diameters (defined as longest extent along any axis) of most final wound defects were 1.1 to 2.0 cm (56%) or 2.1 to 3.0 cm (37%). Fifty-four percent of wounds were repaired by primary closure, 20% with local flaps, and 10% with skin grafting, with the remaining 15% left to heal by second intent (10%) or referred for repair (5%). Experience-related differences were detected in defect size and closure technique: defects less than 2 cm in diameter were seen by less experienced surgeons, and defects greater than 2 cm by more experienced surgeons (Wilcoxon's rank-sum test: p=.02). But more experienced surgeons were less likely to use bilayered closures (r=,0.28, p=.036) and undermining (r=,0.28, p=.035). CONCLUSIONS There is widespread consensus among cutaneous surgeons regarding optimal suture selection and closure technique by anatomic location. More experienced surgeons tend to repair larger defects but, possibly because of their increased confidence and skill, rely on less complicated repairs. [source] Fire hazard evaluation of thermoplastics based on analytic hierarchy process (AHP) methodFIRE AND MATERIALS, Issue 5 2010Baogang Yu Abstract Combustibility performance of 14 compositions including five main thermoplastics (polycarbonate (PC), polypropylene (PP), high impact polystyrene (HIPS), acrylonitrile butadiene styrene (ABS) and poly (vinyl chloride) (PVC)) was tested by cone calorimeter. The fire growth index, total heat release amount index, total smoke release amount index and toxicity product index were calculated, based on which an index system for evaluating fire hazard was set up. All factors in this index system had been analyzed by the analytic hierarchy process, and the specific weight for each factor had been determined. Then fire hazard of thermoplastics was evaluated considering integrated fire hazard index. The results show that fire hazards of HIPS-phosphate fire retardant (PFR), PVC-non-flame retardant, ABS-brominated flame retardant (BFR) and PC/ABS-PFR are higher than PC-BFR and PP-non-halogenated flame retardant. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||