The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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High Molecular Weight Polyethylene and Copolymers with 1-Octene Obtained by Metallocene Alcoholates
High molecular weight polyethylene was obtained by the catalytic systems based on alcoholates of metallocenes and methylaluminoxane. These polyethylenes have Mw ranging from 720.000 to 850.000 and low polydispersity. Molecular weight control was made either by hidrogen at low concentrations or by using high polymerization temperatures. The crystalline melting temperature (Tm) of these polymers ranges from 131 to 135°C and the crystallinity degree (xc) was 55%. Polymers with medium Mw (about 500.000) were also obtained and in this case, the crystalline melting temperature was 139°C. Copolymers of ethylene and 1-octene were also obtained with the metallocene alcoholates.
Effect of the Crystallization Rate in the Roughness of Polypropylene Films
The roughness of iso polypropylene films crystallized at different cooling rates was analyzed using atomic force microscopy. For this characterization it was used the methods of variable bandwith (ZMax) and box-counting in order to determinate the fractal or self-afine character of the surfaces and its roughness. The methods and its computational algorithms were evaluated with synthetic profiles obtained with the Weierstrass-Mandelbrot function. We report the observed deviations in roughens, the relationship between both methods and the effect of the cooling rate in the roughness of polypropylene films.
Setting Kinetics of an Acrylic Bone Cement Modified with Different Kinds of Hydroxyapatite
Acrylic bone cements are widely used in orthopedic surgery to fix artificial prostheses in the body osseous structure. One of the most important applications in this area is in Total Hip Arthroplasty (THA). The cement has two main functions: to assure the short and long term anchorage of the implant to the bone, and to allow a better distribution of body loads between the prostheses and the bone (1-3). Nevertheless several adverse effects are associated with the use of bone cements in this field: high temperature of the polymerization reaction m ay cause thermal necrosis to the adjacent bone (4,5), the release of unreacted monomer, methylmethacrylate (MMA), produces chemical dam age in the surrounding tissues, and the shrinkage of the cement upon curing produces gaps in the bone/cement and cement/prostheses interfaces. Curing of the acrylic cement is a complex process and plays an important role in determining its performance and durability in the hum an body. In this work, the influence of hydroxyapatite types on the curing kinetics of acrylic bone cements is presented.
Blends of Polyethylene Terephthalate (PET) and Polyethylene Naphthalate (PEN) Obtained by Reactive Extrusion
Polyethelene terephthalate (PET) is a polymer broadly used in food packing and containers for carbonated beverages. PET is attractive for its transparency, good mechanical properties and low permeability to O2 and CO2. However, an important disadvantage of the PET container is its low thermal resistance that does not allow hot-filling at sterilization temperatures such as 100°C. Polyethylene naphthalate (PEN) has been considered recently as the most promising alternative to PET. It possesses a glass transition temperature of 125°C which is 50°C higher to that of PET. This enables to fill containers made of this polymer at temperatures higher than 100°C. Another advantage of this polymer is its low permeability to O2 and CO2 which may be five times lower that that of PET. This increases the time of storage of the packed products.
Polyimides Based on Bis(o-am ino)Phenols or Aromatic Tetraamines: Synthesis and Chemical Reactions
Ortho substituted polypyromellitimides were prepared from ortho bis(amino)-phenols or tetraamines by means of either high temperature thermal treatment or low temperature catalytic imidization of poly(amic acid)s, PAAs. Cyclodehydration of the precursors, with ortho OH or NH2 groups in the diamine moieties, in the presence of aliphatic anhydrides and tertiary amines was accompanied by the formation of pendant acetate or acetamide groups, respectively. It was found that model compounds N-(2- hydroxyphenyl)- and N-(2-aminophenyl)- phthalamic acids cyclodehydrated spontaneously to form the corresponding imides at room temperature in aqueous media in the absence of any dehydration agent. A similar effect was observed for the o-hydroxy- and o-amino- polyimides. Treatment of N-(2-aminophenyl)-phthalamic acid with trifluoroacetic anhydride led to the isoimide with an ortho trifluoroacetamide group in the diamine moiety. This thermodynamically unstable compound easily underwent secondary cyclization to yield the ladder 1,2-benzoylenebenzimidazole structure. A higher yield was attained in this reaction when the number of atoms that form the heterocyclic rings was increased.
Aromatic Polyimides Based on 4,4-Diaminotriphenylmethane
The monomer 4,4’-diaminotriphenylmethane (DA-TPM) was used for the first time in the synthesis of aromatic polyimides (PI-TPM) by Koton and coworkers in 1980.1 The polyimides, obtained from DA-TPM and 1,2,4,5-benzotetracarboxylic (PMDA) or oxydiphtalic (ODPA) dianhydrides by thermal ciclodehydration of the precursor polyamic acids (PAA), were very brittle and insoluble in any organic solvent. These disadvantages resulted in an underestimation of the DA-TPM as a monomer for more than fifteen years. A new attempt for the use of 4,4’-diaminotriphenylmethane for the synthesis of polyimides was undertaken in 1995.2 In that work, the polyamic acids based on DA-TPM and PMDA or 3,3’,4,4’-benzofenonetetracarboxylic dianhydride (BTDA) were converted to the final polyimides by catalytic ciclodehydration at room temperature in the presence of acetic anhydride and a tertiary amine. In contrast to the results of Koton et. al.,1 the polymers prepared by this technique showed a good solubility in amide solvents, pyridine and, at high temperatures, in phenolic solvents such as m-cresol, nitrobenzene, etc. Their films exhibit good mechanical properties including high elasticity.
Morphological Stability of Postconsumer PET/HDPE Blends
The morphological stability of postconsumer PET/HDPE blends was studied. Blends at different composition of PET in HDPE, with and without compatibilizer (Kraton G-1652) were prepared in an internal mixer (HAAKE Rheomix 600) and in a twin screw extruder (LEISTRITZ). The mixtures from the extruder were obtained at different stretching ratios (VR/VE). From the morphological analysis of the blends, it is shown that when the copolymer is added to the mixtures, the particle size of the dispersed phase diminishes in some cases until 40% compared with un-compatibilized blends. Moreover, for the case of un-compatibilized blends, (previously prepared by extrusion), the particle size of the dispersed phase increases after being reprocessed in an internal mixer. This result is attributed to the coalescence phenomena that takes place during mixing process. In the case of compatibilized blend, the particle size and the average volume of the dispersed phase remain constant after to be re-processed. In this way, the compatibilizer reduces the interfacial mobility, the coalescence effects and stabilizes the morphology. Tensile mechanical properties confirm this result. Blends containing 10, 20, and 30 %vol. of PET in HDPE with Kraton indicate a strong influence of this copolymer on their properties.
Effect of Vinyl Silane Grafted Polypropylene on Foamability of Thermoplastic Vulcanizate Containing a Water Releasing Compound
Addition of vinyl silane grafted polypropylene to Sarlink® chemical foaming composition containing a water releasing compound was found to increase the extruder head pressure, foam diameter, and foam cell size in the extrusion foaming process. The resulting foams were found to have better compression set properties than the control samples containing no vinyl silane grafted polypropylene. The improvement in foamability was believed to be due to crosslinking and/or chain branching that took place involving vinyl silane groups in the polypropylene phase in the presence of water during the extrusion foaming process.
Effect of Polyamide Grafted Compatibilizer on the Adhesion of Thermoplastic Vulcanizates to Polyamide Substrates
Addition of polyamide (PA) grafted compatibilizer to Polypropylene (PP) and ethylene-propylene terpolymer (EPDM) was found to increase the adhesion strength significantly in polyamide injection overmolding and coextrusion processes. Transmission Electron Microscopy studies show that after melt blending grafted-polyamide compatibilizer with thermoplastic vulcanizates (TPV), the polyamide is present as small distinctive particles in the PP matrix of the thermoplastic vulcanizate. During injection overmolding onto polyamide, a thin layer seems to be formed on the polyamide substrate and thermoplastic vulcanizate interface. Parameters like molecular weight of the grafted compatiblizer and compatibilizer content have been varied to optimize the adhesion strength of TPV to polyamide substrates.
Properties Evaluation of Polyurethane Sandwich Panels with Plastic and Aluminum Skins: Thermal Insulation
Sandwich Panels have a wide field of use in applications such as construction of industrial and commercial buildings, insulation, etc. For large span sandwich panels, as used in housings, usage of thin and strong skins is a necessity. Among metals, an obvious candidate for skin is Aluminum (Al) because of its lightness. However, using plastics could further reduce a great deal of weight. A competitive candidate, in terms of strength, is Polycarbonate (PC), which is currently used in housing applications, in single or double sheets. Under a marketing motivation, an investigation was conducted to compare the properties of sandwich panels with polyurethane (PU) as a core material with two different skins; Al and PC. One of the primary aspects of the research was to theoretically asses thermal insulation performance of both panels with main emphasize on the solar radiation. The governing equations and boundary conditions were numerically solved. The results show that the skin absorptivity, core thickness, and core conductivity are the main parameters to control thermal insulating performance of a sandwich panel.
Effect of Multi-Functional Comonomers on the Properties of Poly(ethylene terephthalate) Copolymers
The properties of poly(ethylene terephthalate) (PET) and its copolymers containing 0.04~0.15 mol% pentaerythritol and trimethylolethane (TME) were investigated. The molecular weight of the copolymers increased with the comonomer content, and its effect was observed significantly in pentaerythritol copolymers, resulting in broad molecular weight distribution. The comonomer effect on the mechanical properties was not considerable. The shear viscosity of the copolymers showed the shear thinning at experimental shear rate range. The crystallization rate of the fiber containing 0.103 mol% pentaerythritol increased with the spin draw ratio and their birefringence was also increased, whereas decreased with the content of comonomer.
Mechanical and Rheological Properties of Liquid Crystalline PHB/PEN/PET Blends
Mechanical and rheological properties of blends of a para hydroxy benzoate - ethylene terephthalate copolyester TLCP (PHB 80 / PET 20 mole%) with Poly(ethylene 2,6-naphthalate) (PEN) and Poly (ethylene terephthalate) (PET) were investigated. Torque values of blends with increasing PHB content abruptly decreased above 40 wt% of PHB content because the melt viscosity of ternary blends were decreased. Tensile strength and tensile modulus of blends containing above 30 wt% PHB were improved with increasing PHB content due to the formation of fibrous structure. The blend of 40 wt% PHB showed pseudo LC phase, and mechanical property was improved with thermal treatment. Rheological property changes with shear rate and processing temperature will be presented.
A Method for Robust Flexible Design
The robust design method aims to seeks to minimize the sensitivity of performance to uncontrolled variation. Product development frequently uses numerical simulations, analytic models and experimental data. However, these underlying predictions may be inaccurate, and include errors that causes the design to be unacceptable and require a design change. This paper presents a method that analyzes the possibility of a design change based on prediction uncertainty, and then estimates possible changes and evaluates the product design flexibility. The results indicate that small changes in design variables to increase robustness may reduce the likelihood and cost of future design changes.
Linking Design to Analysis: The Future of Simulation for Injection Molding
In recent years designers of injection molded parts have widely adopted solid modeling techniques. The time to derive and prepare an analysis model has become burdensome. This is because conventional CAE analysis of injection molding has made extensive use of the Hele-Shaw approximation to simplify the equations governing the process. A consequence of this simplification is the need to generate a midplane mesh. This example of a technical limit hindering the use of a technology has changed with developments arising from Moldflow's product philosophy of Process Wide Plastics Simulation". PWPS has been enabled by three new technologies. In this paper we discuss these developments and how they will change the way analysis influences the design of injection molded plastic Parts"
Automatic Design Optimization Molding Simulation for Injection Molded Parts
The past five years have seen drastic improvements in injection molding simulation. While prior to this period, advanced simulations provided a wealth of information about a part and mold design, a common complaint was that too much time was required to perform an advanced simulation. This is part of the reason for the rise in popularity of desktop" simulations which provide fast useful results though not as detailed as advanced simulations. Besides improving part quality and reducing part costs one of the primary objectives of molding simulation use is to reduce the design cycle and the time to get a mold into production. This paper discusses recently developed molding simulation technology which greatly reduces the time requirement to run an advanced simulation and reduces the overall product development time."
Injection Molding Process Control
Injection molders require a consistent optimization strategy for machine set-up and production control. The ultimate aim of an injection molding machine is to achieve 100% automatic inspection and quality control of all manufactured parts, where no unacceptable moldings are passed on to the customer. Process monitoring and control offers a key opportunity to the polymer processing industry enabling it to gain an understanding of its processes, to dispel its 'black art' image, and by this provide greater clarity for the machine operators and greater confidence for its expanding and highly competitive markets. The next major development for injection molding machine controllers is the integration of 'industry focussed' expert systems for process optimisation and production control. These expert systems will provide a well documented link between design and process engineering, passing information in both directions.
A Comparative Study of the Melting and Crystallization Behavior for a Metallocene and a Narrow Fraction of Ziegler-Natta Isotactic Polypropylene
A comparative study of the melting and crystallization behavior is carried out between a metallocene type isotactic polypropylene and a narrow fraction of a Ziegler-Natta type with the same average defect content. At any crystallization temperature the melting temperature of the Ziegler fraction is ~ 3.5 °C higher than the metallocene. This difference is associated with the thicker lamellae thicknesses found in the fraction. The lamellae thicknesses were obtained by AFM, TEM and SAXS and good agreement was obtained between these techniques. The difference in thicknesses is interpreted as a consequence of a sustained heterogeneity of the intermolecular defect composition distribution in the Ziegler fraction even after fractionation. A second source for this difference could be a different partitioning of the defects present in the metallocene and in the fraction between the crystalline and the non crystalline phases. The product of the interfacial free energies obtained from nucleation theory, is very similar for both isotactic polypropylenes.
Processability and Mechanical Properties of Metallocenic s-PP/Conventional i-PP Blends
Polypropylene with especial properties can be obtained by metallocenic catalysts, which represented the beginning of a new era in the polyolefins technology. In this context, some properties and principally some applications of sindyotatic polypropylene (s-PP) have not been well investigated. In this work, the influence of the metallocenic s-PP addition on the processability and on the mechanical properties of isotatic polypropylene (i-PP) was evaluated. It was observed that an increasing addition of s-PP promoted better processabilility, with an increasing in the impact strength. It was also verified a decreasing in the crystallinity of the blends, resulting in a decreasing in the stress at yield and module.
Interfacial Tensions in Polyolefin Blends
The interfacial tension between immiscible polymers is difficult to measure due to the high viscosity of molten polymers. Additionally, the lack of optical contrast that exists between two molten polyolefins renders conventional optical methods impractical. Small-amplitude oscillatory shear flow provides an indirect technique for measuring the interfacial stress between immiscible polyolefin binary blends. Based on the model of Palierne, the interfacial contribution to the measured rheological response is governed by the ratio of the interfacial tension to the average radius of the dispersed droplets. In this work we have investigated the use of amplitude oscillatory shear measurements to determine the interfacial tension in binary blends of immiscible polyolefins. The two-dimensional droplet morphology in each blend was characterized using tapping-phase AFM. True dispersion phase radii were obtained after converting the measured two-dimensional size distributions to three-dimensional size distributions through the linear transformation method of Schwartz-Saltykov. Results of measured interfacial tensions in various polyolefin blends are reported. The interfacial tension of a PP/EP blend thus obtained was in agreement with the value calculated from the SANS measurement.
Rheological Properties of in situ Organic Composites
A study to evaluate the rheological properties of organic in situ short polymer fibres (poly(butylene terephtalate) (PBT))/high density polyethylene (HDPE) and high density polyethylene/poly(ethylene-co-vinyl acetate) (HDPE/EVA9) composites has been carried out. The in situ compatibilization of the HDPE/EVA9/PBT systems with the Bu2SnO catalyst was performed. The different systems were melt blended in a twin screw extruder, drawn at the die exit and cooled. The results indicate that it is possible to produce such composites using reactive extrusion for compatibilization and post extrusion drawing to control the aspect ratio of the PBT fibres. Morphological analysis allowed evaluation of parameters such as draw ratio, PBT concentration and compatibilization on the size and shape of the fibrils. Their influence on the solid rheological behaviour is discussed.
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