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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Surface Properties of Amphipathic Films of Natural and Synthetic Polymers
The surface properties of thin film amphipathic proteins (hydrophobins) and Pluronic® (PEO-PPO-PEO) polymers are investigated to evaluate surface lubricity and adhesion on molded polymer surfaces. Hydrophobins are fungal proteins that self-assemble at hydrophilic-hydrophobic interfaces into amphipathic films and Pluronics are nonionic amphiphilic surfactants. Because of their unique properties, they are of interest as models for potential biomedical and pharmaceutical applications. We have studied the self-assembly behavior of hydrophobins and Pluronic® polymers on hydrophobic polymer surfaces and examined the surface hydrophobicity and the lubrication properties.
Polyurethane-Clay Nanocomposites via Bulk-Polymerization Methods
In this study, polyurethane nanocomposites of organically modified clay were synthesized by bulk-polymerization methods and their properties characterized. The polymerization methods took into account the possibility of formation of clay tethered polymer chains via reactions between isocyanate groups in the chains of prepolymer and chain extended polymers with the hydroxyl groups on organic modifier of clay. The thermal and mechanical properties of the resultant materials were evaluated as function of the method of nanocomposites preparation. As high as 110% increase in modulus and 170% increase in tensile strength were observed with only 5wt% organically treated clay particles. The method based on chain-extended polymers performed better than the method based on prepolymer.
Investigation of the Microscopic Origins of the Torque and Normal Force Responses of Glassy Polymers
Under the assumption that glassy polymers are incompressible, the mechanical response of a cylinder of viscoelastic material below the glass transition temperature to a torsional deformation consists of a torque response and a normal force response along the axis of the cylinder. In performing stress relaxation experiments on poly(n-alkyl methacrylate)s, the normal force required to keep the constant deformation is compressive and large. Here we examine the microscopic origins of the nonlinear response functions. We consider the influence of the secondary, sub-vitreous ? relaxation on the normal force response. This is done by performing experiments on poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) which both exhibit a ? peak in the loss modulus as a function of temperature located at the same temperature of 10 °C and having about the same intensity. A surprising result is that although the torque response for the PMMA is 50% higher than for the PEMA, the normal force response for the PMMA is 20% lower than the normal force response of the PEMA at the experimental temperatures of 45 °C and 30 °C.
Hysteresis Loss of Polymeric Materials: Finding of New Dimensionless Parameters
An in-depth experimental and theoretical study of many important factors governing the hysteresis loss of rubber vulcanizates having variation of loading of carbon black, silica, clay, resin, and curatives is carried out over a wide range of strain, strain rate/frequency and temperature. Experimental results reveal that the hysteresis loss depends on the heat generation of rubber vulcanizates, specific heat, thermal conductivity, Young's modulus, filler loading, structure and surface area of the filler, temperature difference between application temperature and glass transition temperature, frequency, temperature difference between wall and environment, stress, and stroke amplitude. To confirm the above statement, the hysteresis loss data are analyzed by dimensionless parameters developed by using both of Buckingham pi-method and Rayleigh method. Based on the analysis, an equation is developed in which hysteresis loss of rubber vulcanizates is expressed in terms of the operating conditions and material properties of elastomers.
Enhanced Toughness Properties in Nanostructured Glassy Polymers by all-Acrylic Block Copolymers Prepared by Controlled Radical Polymerization
All-acrylic block copolymers comprising rigid and rubbery blocks tethered together are prepared by a recently developed Controlled Radical Polymerization process, mediated by the SG1 nitroxide.The self-assembly of block copolymers at a molecular scale produces transparent nanostructures that are thermodynamically robust and can be processed repeatedly while maintaining favorable properties. Besides ductility due to confinement, nanostructuration of all-acrylic block copolymers can trigger new types of deformation mechanisms under dynamic loading and improve the toughness properties.
A Novel Understanding on the Effects of Industrial Retorting in Ethylene-Vinyl Alcohol Copolymers Used in Retortable Food Packaging Applications
The ethylene-vinyl alcohol (EVOH) copolymers are a family of excellent high barrier resins with wide implementation in a number of oxygen sensitive food packaging applications. These materials are also widely used in retortable food packaging designs, where the multilayer structure, e.g. PP/EVOH/PP, is temporarily exposed to water vapour to render the packaged food sterile. This thermal treatment is known to lead to a deterioration in the oxygen barrier performance of the EVOH internal layer present in the structure. The previous understanding of this phenomenon suggested a plasticization process by which ingress of water through the external hydrophobic layers, e.g. polypropylene (PP), reached the high barrier EVOH layer. On the other hand, the results presented here clearly indicate that, in addition to water ingress and subsequent material plasticization, a crystallinity disruption is also taking place during retorting. Nevertheless, this crystallinity disruption can be effectively overcome, and, therefore, the packaged food safety be ensured, by, for instance, adequate drying/annealing of the packaging structure after the retorting treatment. Unprecedented time-resolved WAXS analysis of a PP/EVOH32/PP multilayer permitted us to determine that EVOH32 does actually resist the retorting process when protected between PP layers.
Development of EVOH-Kaolinite Nanocomposites for High Barrier Packaging Applications
This paper reports on a novel route to develop EVOH-kaolinite nanocomposites by a melt intercalation process and on some relevant nanocomposite properties as a function of composition. The kaolinite clay used is a very cheap raw material of the tile industry and as such needed to be refined and chemically modified prior to the melt intercalation step. The modification was carried out with dimethyl-sulfoxide, methanol and octadecylamine in order to increase the basal plane distance of the original clay by a factor of more than three. Wide-angle X-ray diffraction (WAXD), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) were used for characterization of the morphologies obtained. From the early results, partial exfoliation and intercalation of the clay platelets was the dominant morphology attained. The dispersion of clay nanolayers in the EVOH matrix seeks to improve the barrier properties of EVOH. An increase in thermal resistance, glass transition temperature, crystallinity and barrier properties to oxygen were also observed for mass clay loadings below 8%.
Biaxial Orientation in Polyethylene Films: Comparison of Infrared Spectroscopy and X-Ray Techniques
In this study, different polyethylene films (LDPE, LLDPE and HDPE) were produced under using different processes (film blowing and biaxial orientation) and processing conditions. The orientation of the films was characterized in terms of their biaxial crystalline, amorphous and global orientation factors using birefringence, Fourier Transform Infrared Spectroscopy (FTIR) with a tilted incidence technique and X-ray pole figures. It is well established that FTIR can measure crystalline axes orientation for polyethylenes, as well as the orientation of the amorphous phase. On the other hand, X-ray pole figures determines the orientation of the crystalline axes, and in combination with birefringence can yield the amorphous phase orientation. The results from those techniques are compared and discussed in terms of the accuracy of the techniques and the contributions of different specific entities in FTIR measurements.
Evidence of Dual Phase for the Amorphous State of Polymers from Crystallization Kinetics
We analyze constant rate cooling and heating crystallization kinetics of PET samples by DSC. The samples have various degree of disentanglement, obtained by the new TekFlow processing technology. According to EKNET interactive Dual Phase model, the amorphous state is made up of two coupled and interactive amorphous phases. These two phases have distinct viscoelastic and thermodynamic characteristics (Tg, free volume, G' and G etc.) which are determined by the potential energy of the conformers and by the state of entanglement of the macromolecular coils.Semi-crystalline polymers such as Polyethylene Terephtalate (PET) are amorphous in the molten state and should have Dual Phase behavior. The phase duality should manifest itself during crystallization from the melt during cooling or during cold crystallization while heating quenched samples.The purpose of this communication is to quantitatively describe the kinetics of crystallization of PET samples with a dual phase kinetics formulation and determine the respective influence of molecular weight and degree of entanglement on the kinetics parameters rate of crystallization and percentage of crystallinity."
The Influence of Ionic Functionality on the Interfacial Tension in Polypropylene/Copolyester Blends
The interfacial tension of binary blends of an amorphous copolyester, poly(ethylene-co-cyclohexane 1,4-dimethanol terephthalate) (PETG) and an itaconic acid grafted polypropylene (PP-g-IA) have been investigated in order to elucidate the effect of ionic incorporation on interfacial tension. PP-g-IA was formed through reactive extrusion using dicumyl peroxide as the initiator with neutralization agents of zinc and magnesium oxide. Interfacial tension was determined using the breaking thread method (BTM). Reductions in interfacial tension have been seen with the grafting of itaconic acid onto PP, with neutralized PP-g-IA showing further reductions in the interfacial tension between the blend components.
In-Situ Ultrasonic Compatibilization of Dynamically Vulcanized PP/EPDM Blends
Dynamically vulcanized PP/EPDM blends were treated by high intensity ultrasonic waves during extrusion. These blends were compared with unvulcanized PP/EPDM blends that were treated by ultrasound during extrusion and then dynamically vulcanized. Die pressure and power consumption were measured. The effect of different gap sizes, ratio of components, and number of ultrasonic horns were investigated. The rheological properties, morphology and mechanical properties of the blends with and without ultrasonic treatment were compared. The results obtained indicated that ultrasonic treatment induced the thermo-mechanical degradation causing enhanced molecular transport and chemical reactions at the interfaces, thus leading to in-situ compatibilization, which is evident by the morphological and mechanical property studies. Processing conditions were established for enhanced in-situ compatibilization of the dynamically vulcanized PP/EPDM blends.
Photomechanical Oxidation of Anisotropic Polyethylene
Blown polyethylene film was exposed to ultraviolet (UV) irradiation while under stress applied (i) parallel and (ii) perpendicular to the machine direction. Oxidation was followed using the FTIR carbonyl index and was found to accelerate under tensile stress. Some samples broke during UV-tension exposure and did so in a shorter time when stress was applied in the machine direction than when it was applied in the transverse direction. Samples with different TiO2 pigments gave different rates of carbonyl development; some showed greater acceleration when stress was applied parallel to the machine direction, others when it was applied transversely. The carbonyl index was approximately the same at break for all longitudinally stressed samples and a higher carbonyl index was found at the onset of cracking for transversely strained samples.
Biaxial Orientation of Multilayer LDPE/PET Films: Structure and Properties
In this study, initially thick low density polyethylene / polyethylene terephthalate (LDPE/PET) multilayer blown films were biaxially stretched at different temperatures. The effect of draw temperature and draw speed as well as adhesion between the LDPE and PET layers, through a middle tie layer, on orientation and some properties is studied. The properties of interest are tensile properties, tear, impact strength and haze. The results indicate that the tie layer enhances the properties of stretched films and that toughness is strongly affected by draw ratio and little by draw speed and temperature in the ranges studied.
Haze Improvement with Addition of HP-LDPE or HDPE; Part II - Mechanistic Understanding
Adding small amounts (less than 10%) of High Pressure Low Density Polyethylene (HP-LDPE) or High Density Polyethylene (HDPE) to a Metallocene Linear Low Density Polyethylene (mLLDPE) led to a reduction in haze of the resulting blown films. It was found that for both systems the haze reduction was mainly due to the reduction of surface roughness. mLLDPE films shows a rough surface with large lamellar aggregates or spherulitic superstructure. By adding HP-LDPE or HDPE to mLLDPE, the lamellar aggregates became smaller or the structure became simply a row structure in HP-LDPE blends. Both changes led to smoother surfaces. Although majority of the haze came from the light scattering of the rough film surface, the similarity between surface morphology and bulk morphology suggests that haze could be correlated to the bulk structure. In fact, it was found that the haze showed a good correlation with lamellar orientation. Blends with a higher lamellar orientation showed lower haze. Attempt to correlate haze with overall melt elasticity was not successful. The results suggested that the overall melt elasticity was not the dominate factor for forming oriented lamellae. Instead, the formation of oriented lamellae is promoted by the small amounts of molecules with extremely long relaxation times, which behave as oriented nuclei.
Predictions of MD Tear Strengths of Some Solution Octene LLDPE Film Resins
By incorporating both polymer properties and processing variables, a robust model has been developed through multivariate statistical analysis for the MD tear strengths of some solution octene LLDPE resins produced using NOVA Chemicals' Advanced SCLAIRTECH technology. It is found that the model is applicable to different resins and processing conditions. The model suggests that MD tear strength is a nonlinear function of polymer properties, machine direction strain rate and process time. It has demonstrated its utility in product development at extrusion film lines of different dimensions, and to resins produced at both pilot and commercial scales.
Linear and Non-Linear Biaxial Stress-Optical Behavior in PET Films as Observed by Real Time True Stress-True Strain-Birefringence Technique
Biaxial stretching of polymer films such as PET is a common process in the industry. Being able to monitor the stress-strain mechanical behavior of the films during stretching and linking this with the birefringence behavior provides a good tool to investigate stress and strain optical behavior of these films undergoing complex structural organization The results indicate that PET exhibits four stage stress optical behavior in simultaneous biaxial mode. The first stage is traditional linear stress optical behavior with stress optical constant (SOC) of 5.8 GPa-1 (5800 Brewsters). In the second stage birefringence rapidly increases and this is typically associate with the formation of poorly ordered crystals that are assumed to be at the nodes of the physical network. In the third stage the birefringence begins to level off with considerable negative slope variation with stress where the crystallinity further develops. The fourth stage was observed only at high stretching rates and in this distinct stage, birefringence become near constant while stress continues to increase as the chains have reached their full extensibilities.
The Effect of Maleic Anhydride Coupling Agent on Melt Processed Semi-Crystalline PET Nanocomposite Films
Semi-crystalline PET/montmorillonite nanocomposite films were processed by melt-extrusion along with 0.5% maleic anhydride as a coupling agent. Mechanical, thermal, barrier and morphological properties of the nanocomposite films with and without the coupling agent were examined. The nanocomposites have demonstrated an intercalated/exfoliated morphology with the montmorillonite acting as a crystal-nucleating agent in all of the nanocomposite film samples. DSC experiments show this effect through faster nucleation rates and an increased overall degree of crystallization. A depressed glass transition temperature is observed in all nanocomposite samples along with an increased Young's modulus and decrease in film toughness.
The Influence of Molecular Weight on the Relaxation Behavior of Uniaxially Strethed PEN Films as Investigated by Real Time Spectral Birefringence Technique
The influence of molecular weight (Mw) on the structural evolution of as cast amorphous poly (ethylene naphthalene), PEN, during uniaxial stretching and further relaxation is investigated by real time measurement of the true mechanical and optical behavior of the material in the rubbery state. Uniaxial deformation behavior reveals that stress-optical behavior is composed of three regions: (I) traditional stress optical region where the polymer remains amorphous, (II) fast birefringence increase region that accompany rapid rise in crystallinity and (III) birefringence saturation region. Both materials follow the stress optical rule (SOR) at low deformation levels with a stress optical constant of 27.5 GPa-1. Stress-optical behavior deviates from linearity in both MW PEN's when crystallinity exceeds 7% and the material exhibit nematic order. The deviation from linearity occurs at lower stress levels for the low MW material, nevertheless. The mechanism of neck formation has a considerable influence on the crystallization of the material. After neck starts the crystallinity increases rapidly in both materials, reaching a saturation value of approx. 35% in crystallinity when strain hardening occurs. The preliminary studies revealed that the relaxation behavior of PEN involves a complete orientation recovery following the stress optical rule when the material is first stretched within the Region I and if stretched beyond the linear range the relaxation stage is found to accompany partial orientation relaxation followed by crystallization.
Haze Improvement with Addition of HP-LDPE or HDPE: Part I - Blown Film Property Comparison
Blends of a Metallocene Linear Low Density Polyethylene (mLLDPE) with a variety of high pressure Low Density Polyethylene (HP-LDPE) or High Density Polyethylene (HDPE) at different blend ratios were investigated. Effects of these additions on blown film haze and toughness are discussed.Dramatic improvement in haze is achievable either by HP-LDPE addition or by HDPE addition. The improvement in haze, however, is usually accompanied with losses in mechanical property. Careful choice of blending partner and level is crucial for the best balance of haze and mechanical properties.
The Influence of Draw Conditions on the Morphology and Physical Performance of POE Film
The influence of draw conditions on the morphology and physical performance of polyethylene-octene elastomer(POE) film were studied in this paper. The influence of draw conditions on the morphology of POE film was discussed via wide-angle X-ray diffraction (WAXD). The results showed that draw conditions caused POE film to produce a (110) plane crystalline peak in PE. When the draw ratio (DR) = 3, the interference intensity at draw temperature (DT) = 90? was greater than that at DT = 75?; and when DR = 6, the interference intensity at DT = 75? was greater than that at DT = 90 ? . Elastic recovery rate and stress-strain value were tested using an Instron multi-testing machine. The results were used to establish a dynamic deformation mechanism. The results showed that, after draw processing of POE, the stress value fell after approaching the saturation point with the increase in draw ratio. Furthermore, it was also shown that the elastic recovery rate and stress retention rate were better at DT = 75? than at DT = 90?.
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