Modification of Polyethylenes by Reactive Extrusion

The main aim of the study was to optimise the reactive extrusion conditions in the conventional modification processes of polyethylenes in a single screw extruder.The optimum conditions for peroxide crosslinking of low density polyethylene (LDPE), linear low density polyethylene (LLDPE) and their blend were determined in a torque rheometer. The actual reactive extrusion was performed in a laboratory single screw extruder using the optimum parameters. The influence of the coagent, triaUyl cyanurate (TAC), on the cross linking of low density polyethylene in the presence of peroxide was also investigated. The peroxide crosslinking was found to improve the mechanical properties and the thermal stability of the polyethylenes. The efficiency of crosslinking was found to be improved by the addition of coagent such as TAC.The optimum conditions for silane grafting viz temperature, shear rate, silane and DCP concentrations were determined on a torque rheometer in the case of LDPE, LLDPE and their blend. Silane grafting of LDPE in the presence of peroxide was performed with and without addition of water. Compounding of such mixtures in the melt at high temperatures caused decomposition of the peroxide and grafting of alkoxy silyl groups to the polyethylene chains.The optimum parameters for maleic anhydride modification of LDPE, LLDPE and their blend were determined. The grafting reaction was confinned by FTIR spectroscopy. Modification of polyethylenes with maleic anhydride in the presence of dicumyl peroxide was found to be useful in improving mechanical properties. The improvement was found to be mainly due to the grafting of carboxyl group and formation of crosslinks between the chains. The cross linking initiated improvements indicate extended property profiles and new application fields for polyethylenes.On the whole the study shows that the optimum conditions for modifying polyethylenes can be determined on a torque rheometer and actual modification can be performed in a single screw extruder by employing the optimum parameters for improved mechanical! thermal behaviour without seriously affecting their processing behaviour.

Oxidation and stabilisation chemistry of metallocene-based polyolefins during melt processing

Metallocene catalyzed linear low density polyethylene (m-LLDPE) is a new generation of olefin copolymer. Based on the more recently developed metallocene-type catalysts, m-LLDPE can be synthesized with exactly controlled short chain branches and stereo-regular microstructure. The unique properties of these polymers have led to their applications in many areas. As a result, it is important to have a good understanding of the oxidation mechanism of m-LLDPE during melt processing in order to develop more effective stabilisation systems and continue to increase the performance of the material. The primary objectives of this work were, firstly, to investigate the oxidative degradation mechanisms of m-LLDPE polymers having different comonomer (I-octene) content during melt processing. Secondly, to examine the effectiveness of some commercial antioxidants on the stabilisation of m-LLDPE melt. A Ziegler-polymerized LLDPE (z-LLDPE) based on the same comonomer was chosen and processed under the same conditions for comparison with the metallocene polymers. The LLDPE polymers were processed using an internal mixer (torque rheometer, TR) and a co-rotating twin-screw extruder (TSE). The effects of processing variables (time, temperature) on the rheological (MI, MWD, rheometry) and molecular (unsaturation type and content, carbonyl compounds, chain branching) characteristics of the processed polymers were examined. It was found that the catalyst type (metallocene or Ziegler) and comonomer content of the polymers have great impact on their oxidative degradation behavior (crosslinking or chain scission) during melt processing. The metallocene polymers mainly underwent chain scission at lower temperature (<220°C) but crosslinking became predominant at higher temperature for both TR and TSE processed polymers. Generally, the more comonomers the m-LLDPE contains, a larger extent of chain scission can be expected. In contrast, crosslinking reactions were shown to be always dominant in the case of the Ziegler LLDPE. Furthermore, it is clear that the molecular weight distribution (MWD) of all LLDPE became broader after processing and tended generally to be broader at elevated temperatures and more extrusion passes. So, it can be concluded that crosslinking and chain scission are temperature dependent and occur simultaneously as competing reactions during melt processing. Vinyl is considered to be the most important unsaturated group leading to polymer crosslinking as its concentration in all the LLDPE decreased after processing. Carbonyl compounds were produced during LLDPE melt processing and ketones were shown to be the most imp0l1ant carbonyl-containing products in all processed polymers. The carbonyl concentration generally increased with temperature and extrusion passes, and the higher carbonyl content fonned in processed z-LLDPE and m-LLDPE polymers having higher comonomer content indicates their higher susceptibility of oxidative degradation. Hindered phenol and lactone antioxidants were shown to be effective in the stabilization of m-LLDPE melt when they were singly used in TSE extrusion. The combination of hindered phenol and phosphite has synergistic effect on m-LLDPE stabilization and the phenol-phosphite-Iactone mixture imparted the polymers with good stability during extrusion, especially for m-LLDPE with higher comonomer content.

Investigation of the oxidative degradation mechanisms and melt stabilisation of a new generation metallocene polytehylene

The two main objectives of the research work conducted were firstly, to investigate the processing and rheological characteristics of a new generation metallocene catalysed linear low density polyethylene (m-LLDPE), in order to establish the thermal oxidative degradation mechanism, and secondly, to examine the role of selected commercial stabilisers on the melt stability of the polymers. The unstabilised m-LLDPE polymer was extruded (pass I) using a twin screw extruder, at different temperatures (210-285°C) and screw speeds (50-20rpm) and was subjected to multiple extrusions (passes, 2-5) carried out under the same processing conditions used in the first pass. A traditional Ziegler/Natta catalysed linear low density polyethylene (z-LLDPE) produced by the same manufacturer was also subjected to a similar processing regime in order to compare the processability and the oxidative degradation mechanism (s) of the new m-LLDPE with that of the more traditional z-LLDPE. The effect of some of the main extrusion characteristics of the polymers (m-LLDPE and z-LLDPE) on their melt rheological behaviour was investigated by examining their melt flow performance monitored at two fixed low shear rate values, and their rheological behaviour investigated over the entire shear rates experienced during extrusion using a twin-bore capillary rheometer. Capillary rheometric measurements, which determine the viscous and elastic properties of polymers, have shown that both polymers are shear thinning but the m-LLDPE has a higher viscosity than z-LLDPE and the extent of reduction in viscosity of the former when the extrusion temperature was increased from 210°C to 285°C was much higher than in the case of the z-LLDPE polymer. This was supplied by the findings that the m-LLDPE polymer required higher power consumption under all extrusion conditions examined. It was fUliher revealed that the m-LLDPE undergoes a higher extent of melt fracture, the onset of which occurs under much lower shear rates than the Ziegler-based polymer and this was attributed to its higher shear viscosity and narrower molecular weight distribution (MWD). Melt flow measurements and GPC have shown that after the first extrusion pass, the initial narrower MWD of m-LLDPE is retained (compared to z-LLDPE), but upon further multiple extrusion passes it undergoes much faster broadening of its MWD which shifts to higher Mw polymer fractions, paliicularly at the high screw speeds. The MWD of z-LLDPE polymer on the other hand shifts towards the lower Mw end. All the evidence suggest therefore the m-LLDPE undergoes predominantly cross-linking reactions under all processing conditions whereas z-LLDPE undergoes both cross-linking and chain scission reactions with the latter occurring predominantly under more severe processing conditions (higher temperatures and screw speeds, 285°CI200rpm). The stabilisation of both polymers with synergistic combinations of a hindered phenol (Irganox 1076) and a phosphite (Weston 399) at low concentrations has shown a high extent of melt stabilisation in both polymers (extrusion temperatures 210-285°C and screw speeds 50-200rpm). The best Irganox 1076/Weston 399 system was found to be at an optimum 1:4 w/w ratio, respectively and was found to be most effective in the z-LLDPE polymer. The melt stabilising effectiveness of a Vitamin E/Ultranox 626 system used at a fraction of the total concentration of Irganox 1076/Weston 399 system was found to be higher in both polymers (under all extrusion conditions). It was found that AOs which operate primarily as alkyl (Re) radical scavengers are the most effective in inhibiting the thermal oxidative degradation of m-LLDPE in the melt; this polymer was shown to degrade in the melt primarily via alky radicals resulting in crosslinking. Metallocene polymers stabilised with single antioxidants of Irganox HP 136 (a lactone) and Irganox E201 (vitamin E) produced the highest extent of melt stability and the least discolouration during processing (260°C/1 OOrpm). Furthermore, synergistic combinations of Irganox HP I 36/Ultranox 626 (XP-60) system produced very high levels of melt and colour stability (comparable to the Vitamin E based systems) in the mLLDPE polymer. The addition of Irganox 1076 to an Irganox HP 136/Ultranox 626 system was found not to result in increasing melt stability but gave rise to increasing discolouration of the m-LLDPE polymer. The blending of a hydroxylamine (lrgastab FS042) with a lactone and Vitamin E (in combination with a phosphite) did not increase melt stability but induced severe discolouration of resultant polymer samples.

Metallocene ethylene-1-octene copolymers:effect of extrusion conditions on thermal oxidation of polymers with different comonomer content

Metallocene ethylene-1-octene copolymers having different densities and comonomer content ranging from 11 to 36 wt% (m-LLDPE), and a Ziegler copolymer (z-LLDPE) containing the same level of short-chain branching (SCB) corresponding to one of the m-LLDPE polymers, were subjected to extrusion. The effects of temperature (210-285 °C) and multi-pass extrusions (up to five passes) on the rheological and structural characteristics of these polymers were investigated using melt index and capillary rheometry, along with spectroscopic characterisation of the evolution of various products by FTIR, C-NMR and colour measurements. The aim is to develop a better understanding of the effects of processing variables on the structure and thermal degradation of these polymers. Results from rheology show that both extrusion temperature and the amount of comonomer have a significant influence on the polymer melt thermo-oxidative behaviour. At low to intermediate processing temperatures, all m-LLDPE polymers exhibited similar behaviour with crosslinking reactions dominating their thermal oxidation. By contrast, at higher processing temperatures, the behaviour of the metallocene polymers changed depending on the level of comonomer content: higher SCB gave rise to predominantly chain scission reactions whereas polymers with lower level of SCB continued to be dominated by crosslinking. This temperature dependence was attributed to changes in the different evolution of carbonyl and unsaturated compounds including vinyl, vinylidene and trans-vinylene. © 2007 Elsevier Ltd. All rights reserved.

Experimental Modeling of Twin-Screw Extrusion Processes to Predict Properties of Extruded Composites

Twin-screw extrusion is used to compound fillers into a polymer matrix in order to improve the properties of the final product. The resultant properties of the composite are determined by the operating conditions used during extrusion processing. Changes in the operating conditions affect the physics of the melt flow, inducing unique composite properties. In the following work, the Residence Stress Distribution methodology has been applied to model both the stress behavior and the property response of a twin-screw compounding process as a function of the operating conditions. The compounding of a pigment into a polymer melt has been investigated to determine the effect of stress on the degree of mixing, which will affect the properties of the composite. In addition, the pharmaceutical properties resulting from the compounding of an active pharmaceutical ingredient are modeled as a function of the operating conditions, indicating the physical behavior inducing the property responses.

Volatile compounds in the thermoplastic extrusion of bovine rumen

The volatile compounds of raw and extruded bovine rumen, extracted by dynamic headspace, were separated by gas chromatography and analyzed by GC-MS. Raw and extruded materials presented thirty-two volatile compounds. The following compounds were identified in raw bovine rumen: heptane, 1-heptene, 4-methyl-2-pentanone, toluene, hexanal, ethyl butyrate, o-xylene, m-xylene, p-xylene, heptanal, limonene, nonanal, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane and octadecane. The following compounds were identified in the extruded material: 1-heptene, 2,4-dimethylhexane, toluene, limonene, undecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane and nonadecane. Mass spectra of some unidentified compounds indicated the presence of hydrocarbons with branched chains or cyclic structure.

Recovery and upgrading bovine rumen protein by extrusion: effect of lipid content on protein disulphide cross-linking, solubility and molecular weight

Bovine rumen protein with two levels of residual lipids (1.9 per cent or 3.8 per cent) was subjected to thermoplastic extrusion under different temperatures and moisture contents. Protein solubility in different buffers, disulphide cross-linking and molecular weight distribution were determined on the extrudates. After extrusion, samples with 1.9 per cent residual lipids content had a higher concentration of protein insoluble by undetermined forces, irrespective of feed moisture and processing temperature used. Lipid content of 3.8 per cent in the feed material resulted in more protein participating in the extrudate network through non-covalent interactions (hydrophobic and electrostatic) and disulphide bonds. A small dependency of the extrusion process on moisture and temperature and a marked dependency on lipid content, especially phospholipid, was observed, Electrophoresis under non-reducing conditions showed that protein extrusion with low feed moisture promoted high molecular breakdown inside the barrel, probably due to intense shear force, and further protein aggregation at the die end

Amorphous HfO(2) and Hf(1-x)Si(x)O via a melt-and-quench scheme using ab initio molecular dynamics

We have performed ab initio molecular dynamics simulations to generate an atomic structure model of amorphous hafnium oxide (a-HfO(2)) via a melt-and-quench scheme. This structure is analyzed via bond-angle and partial pair distribution functions. These results give a Hf-O average nearest-neighbor distance of 2.2 angstrom, which should be compared to the bulk value, which ranges from 1.96 to 2.54 angstrom. We have also investigated the neutral O vacancy and a substitutional Si impurity for various sites, as well as the amorphous phase of Hf(1-x)Si(x)O(2) for x=0.25, 0375, and 0.5.

Sugarcane bagasse cellulose/HDPE composites obtained by extrusion

Natural fibers used in this study were both pre-treated and modified residues from sugarcane bagasse. Polymer of high density polyethylene (HDPE) was employed as matrix in to composites, which were prodUced by mixing high density polyethylene with cellulose (10%) and Cell/ZrO(2)center dot nH(2)O (10%), using an extruder and hydraulic press. Tensile tests showed that the Cell/ZrO(2)center dot nH(2)O (10%)/HDPE composites present better tensile strength than cellulose (10%)/HDPE composites. Cellulose agglomerations were responsible for poor adhesion between fiber and matrix in cellulose (10%)/HDPE composites. HDPF/natural fibers composites showed also lower tensile strength in comparison to the polymer. The increase in Young`s modulus is associated to fibers reinforcement. SEM analysis showed that the cellulose fibers insertion in the matrix Caused all increase of defects, which were reduced When modified cellulose fibers were Used. (C) 2008 Elsevier Ltd. All rights reserved.

Magnetostriction of melt-spun Fe(85)Ga(15), Fe(78)Ni(7)Ga(15) and Fe(78)Co(7)Ga(15) stacked ribbon samples

A set of stacked ribbon samples with the compositions Fe(85)Ga(15), Fe(78)Ni(7)Ga(15) and Fe(78)Co(7)Ga(15) were prepared. XRD on these ribbons show that the binary Fe(85)Ga(15) ribbon exhibits the disordered A2 structure where as the addition of Co and Ni leads to the appearance of an additional ordered DO(3) structure. A comparison of the ratio of the XRD-line intensities gave strong evidence of a (100) texture perpendicular to the ribbon surface. The optical studied microstructure supports these results because it shows a columnar grain growth parallel to the solidification direction-which is parallel to ribbon thickness. The highest magnetostriction was found for Fe(78)Ni(7)Ga(15) (370 ppm), while the Fe(78)Co(7)Ga(15) a smaller magnetostriction of 270 ppm was found. The enhancement of the magnetostriction is attributed to the (100) texture in these ribbons. (C) 2009 Elsevier B.V. All rights reserved.

Thermoplastic starch modified during melt processing with organic acids: The effect of molar mass on thermal and mechanical properties

Thermoplastic starch (TPS) was modified with ascorbic acid and citric acid by melt processing of native starch with glycerol as plasticizer in an intensive batch mixer at 160 degrees C. It was found that the molar mass decreases with acid content and processing time causing the reduction in melting temperature (T(m)). As observed by the results of X-ray diffraction and DSC measurements, crystallinity was not changed by the reaction with organic acids. T(m) depression with falling molar mass was interpreted on the basis of the effect of concentration of end-chain units, which act as diluents. FTIR did not show any appreciable change in starch chemical compositions, leading to the conclusion that the main changes observed were produced by the variation in molar mass of the material. We demonstrated that it is possible to decrease melt viscosity without the need for more plasticizer thus avoiding side-effects such as an increase in water affinity or relevant changes in the dynamic mechanical properties. (C) 2010 Elsevier B.V. All rights reserved.

Microstructure and texture of duplex stainless steel after melt-spinning processing

The microstructure and texture of melt-spun UNS S31803 (DIN W. Nr. 1. 4462) duplex stainless steel were analyzed after casting and solution treatment. The cast ribbons contained austenite (gamma) and ferrite (alpha or delta) with roughly equal compositions. The alpha and gamma had < 100 > and < 110 > partial fiber textures, respectively. After solution treatment, the texture was maintained, the amount of gamma phase increased, and the alloying elements were partitioned as expected, according to whether they were ferrite or austenite stabilizers. (c) 2006 Elsevier Inc. All rights reserved.

Photodegradation of Thermodegraded Polypropylene/High-Impact Polystyrene Blends: Mechanical Properties

The influence of the addition of high-impact polystyrene (HIPS) on polypropylene (PP) photodegradation was studied with blends obtained by extrusion with and without styrene-butadiene-styrene (SBS) copolymer (10 wt % with respect to the dispersed phase). The concentrations of HIPS ranged from 10 to 30 wt %. The blends and pure materials were exposed for periods of up to 15 weeks of UV irradiation; their mechanical properties (tensile and impact), fracture surface, and melt flow indices were monitored. After 3 weeks of UV exposure, all of the materials presented mechanical properties of the same order of magnitude. However, for times of exposure greater than 3 weeks, an increasing concentration of HIPS resulted in a better photostability of PP. These results were explained in light of morphological observations. This increase of photostability was even greater when SBS was added to the blends. It was more difficult to measure the melt flow index of the binary PP/HIPS blends than that of PP for low concentrations of HIPS; this was most likely due to energy transfer between the blend domains during photodegradation. This phenomenon was not observed for the ternary blends. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 770-779, 2011

Development and Characterization of L-Alanyl-L-Glutamine Containing Pellets employing Extrusion-Spheronization Method and Drying Process in Fluidized Bad Equipment.

Development and Characterization of L-Alanyl-L-Glutamine Containing Pellets employing Extrusion-Spheronization Method and Drying Process in Fluidized Bad Equipment"". In this work, five formulations of L-alanyl-L-glutamine (glutamine dipeptide) containing pellets with different drug concentration were developed and evaluated: F1 (9.07%); F2 (17.70%); F3 (27.98%); F4 (37.74%) e F5 (47.53%). Pellets were prepared by extrusion-spheronization method and, further, dried in fluidized bad equipment. The following assays were carried out with the batches obtained: granulometry, friability, true density and morphologic analysis. Between the five formulations evaluated, pellets obtained from F3 present best yield (75.80%), most uniform particle size distribution (89.67% of pellets with size in the range of 0.80 to 1.18), most high true density (2.1634 g/ml) and best aspect (1.0795 +/- 0.0410). Due to these features, pellets obtained from F3 were considered adequate to further polymeric coating process in order to produce a multiparticulate system to prolong L-alanyl-L-glutamine release.

Gastro-resistant Pellets of Didanosine obtained by Extrusion and Spheronization: Assessing the Production Process

The aim this work was develop gastro-resistant pellets of didanosine as well as study the impact on the pellets properties, regarding the way as the binder was added and drying process used. The pellets formation was accompanied by analysis of morphological parameters and didanosine dissolution. In the most cases, pellets showed diameter around 1.0 mm and shape parameters acceptable. The variations of the process did not interfere significantly in pellets size. In turn, drying in fluid bed favored the dissolution of didanosine, in contrast to binder addition on powder form that impaired. In another hand, this last resulted in the best aspect factor (about 1.1). Gastro-resistant pellets showed adequate dissolution, compatible with this type of dosage form. The variables of process studied enabled obtain pellets with characteristics of shape and dissolution just slightly different, indicating flexibility of the formulation for production of gastro-resistant pellets of didanosine.