Structural characterization of polyolefins by pyrolysis—hydrogenation glass capillary gas chromatography

In order to obtain quantitatively specific and high-resolution pyrograms of high polymers, fundamental splitting conditions for pyrolysis—gas chromatography were studied using a vertical micro-furnace type of pyrolyzer attached to a glass capiliary separation column. High-resolution pyrograms were measured for polyolefins such as polyethylenes (PE), polypropylenes (PP) and various kinds of ethylen—propylene copolymers [P(E-co-P)] using a pyrolysis—hydrogenation device. Microstructures such as short branchings for PE, stereoregularities and chemical inversions for PP and sequence distributions for P(E-co-P) are discussed on the basis of the pyrograms.     

Static and shear induced crystallization of glass fiber reinforced poly(m‐xylylene adipamide) with nucleating additives

Static and shear induced crystallization studies were carried out on a glass fiber reinforced poly(m‐xylylene adipamide) with various fiber contents. The crystallization experiments were performed using calorimetry and a shearing hot stage coupled with an optical microscope. The crystallization times were measured as a function of the temperature, the shear rate, and the fiber content. In static conditions, no nucleating ability of the fibers was highlighted. However, the shear treatment led to a substantial decrease of the crystallization times for all materials. Moreover, the shear effect is largely influenced by the fiber content, because the shear really undergone by the matrix between the fibers is locally higher than the nominal shear. A previously proposed crystallization kinetics model based on both Avrami and Hoffman–Lauritzen equations and taking into account the nucleating effect of the shear is improved. Hence, the fibers effect is included taking into account the higher local shear between the fibers. The nucleation rate due to the shear is described by a power law of the shear rate, where the prefactor is linked to the fibers amount. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2982–2992, 2007     

Microwave-assisted extraction by fast sample preparation for the systematic analysis of additives in polyolefins by high-performance liquid chromatography

This paper presents a new approach for complete and systematic analysis of organic additives in polyolefins. The proposed procedure is a convenient combination of sample preparation, performed by microwave-assisted extraction (MAE), and direct chromatographic evaluation of extract by high-performance liquid chromatography coupled with ultraviolet and evaporative light scattering detection. In particular two microwave-assisted processes are reported and discussed: the one-step MAE, useful for additives with low-medium dipolarity (like stabilizers, flame retardant, antistatics, slip and processing agents), and the two-step MAE, useful for additives with either high dipolarity (like organic salts, antigasfading, antiacid, nucleating agent) or high molecular mass (like polymeric hindered amine light stabilizers). Both the proposed processes have been tested on representative additives in five commercially common polymeric matrices, demonstrating their satisfactory analytical results, in terms of repeatability and percentage recoveries, and their good performances, in terms of safety and time/solvent consumption, in comparison with those of traditional extraction methods.     

Radiation-assisted PET recycling using glass fiber reinforcement and reactive additives

Post-consumer poly(ethylene terephtalate) (PET) material has been recycled in an upgrading procedure. Radiation treatment of modest dose (10 kGy) has been applied to activate a reactive additive (epoxy-acrylate, 2% to the PET) to bond together the matrix (recycled PET) and the reinforcement (chopped glass fiber, 10–20% to the PET). Tensile-, bending- and impact-resistance of the treated, recycled PET has been improved significantly. A new composite engineering material has been manufactured this way of reactive reinforcing recycling, surpassing the original, virgin PET especially in impact properties. The new thermoplastic is well suitable for injection molding of technical parts.     

Evaluation of a microwave assisted extraction prior to high performance liquid chromatography for the determination of additives in polyolefins

This work presents a method for the reliable determination and quantitation of frequently used stabilizers in polyolefins. The extraction of the stabilizers from the polymeric matrix was investigated for several different solvents and solvent mixtures in a monomode microwave reaction system. Ethyl acetate showed the best extraction performance with respect to easy and rapid sample preparation. For this solvent, a systematic and comprehensive survey of time- and temperature-dependence of extraction efficiency was carried out. Extractions utilizing ethyl acetate for 30 min at 130 °C showed the best overall performance for all investigated analytes. Additionally, the influence of the physical form of the sample was investigated. The extraction of pellets and powder was compared and, regardless of the physical form, the reproducibility for the whole method developed for all chosen analytes was below 2%.     

Nanoclay synergy in flame retarded/glass fibre reinforced polyamide 6

Exfoliated clay nanocomposites of flame retarded/glass fibre reinforced polyamide 6 were prepared by twin-screw extrusion compounding. A flame retardant system based on phosphorus compounds and zinc borate was used at various levels in glass fibre reinforced PA6 and nanocomposites. Thermal stability and combustion behaviours were evaluated by TGA, LOI, UL94 and cone calorimetry. Substitution of a certain fraction of the flame retardant with nanoclays was found to significantly reduce the peak heat release rate and delay ignition in the cone calorimeter. Moreover, remarkable improvements were obtained in LOI along with maintained UL94 ratings. Residue characterization by FTIR, XRD and SEM ascribed the enhanced flame retardancy of nanocomposite formulations to the formation of a glassy boron/aluminium phosphate barrier reinforced by clay layers at the nanoscale. The physically strong and consolidated barriers formed from nanocomposites were much more effective in impeding heat and mass transfer compared to those from conventional formulations.     

Oxidation of a carbon/glass reinforced cyanate ester composite

The decomposition/oxidation behaviour of a carbon/glass fibre reinforced thermosetting pre-impregnated material based on polymerized aromatic cyanate ester compounds (commercial name GURIT-PN900-C582-43) has been investigated. Experiments were carried out for thermally thick samples exposed in a preheated reaction chamber (temperatures between 650–950 K) and a continuous gas flow (inlet velocity between 0.6 and 4.2 cm/s). Temperature measurements indicate that, in air, the process takes place under a mixed kinetic-diffusive control with three main dynamic stages corresponding to oxidative decomposition, heterogeneous ignition delay and oxidation. The oxidative decomposition stage is always much faster than the total duration of the ignition delay and oxidation stages (factors of 60–85). SEM pictures show dramatic changes in the material structure with amounts of solid residue, at the conclusion of the conversion process, varying from about 62% (resin char, glass and carbon fibres) to 29% (essentially the glass fibres) (against 85–75% for thermal degradation). Also, with the aid of thermogravimetric curves measured in air for the composite material and a charred residue, a three-step oxidation mechanism is proposed consisting of the oxidative decomposition of the resin, the oxidation of the resin char and the oxidation of the carbon fibres with estimated activation energies of 95, 136 and 185 kJ/mol, respectively.     

Apparent shear strength of hybrid glass fibre reinforced composite joints

The incorporation of nano or micro ceramic particles into fibre reinforced composites (FRC) to enhance their stiffness and durability has been widely investigated. This mechanism has been attributed to the increase in stiffness of the polymeric matrix phase and shear strength of FRCs due to the presence of particles at the interlaminar regions. In order to elucidate such effect, hybrid single-lap joints consisted of ceramic particles and glass fibre reinforced composites were evaluated to better assess the mechanical interlocking effect provided by silica and cement inclusions. A full factorial design (2³) was performed to identify the effect of the type of particle (silica and cement), particle weight fraction (2.5 and 5 wt%) and glass fibre grammage (200 and 600 g/m²) on the apparent shear strength and adherent strength of single-lap joints under tensile loading. The ceramic particle inclusions led to increased apparent shear strength and adherent strength. The inclusion of 5 wt% ceramic particles into 600 g/m² cross-ply glass fibre composites enhanced both adherent and apparent shear strengths.     

Epitaxy of helical polyolefins

The structural rules which govern the epitaxial crystallisation of polymers - and especially polyolefins - on organic substrates are established. Illustrative examples involve isotactic and syndiotactic polypropylenes and poly( l-butene). Investigation of the film structure by electron microscopy, electron diffraction and atomic force microscopy reveals some unprecedented features, including in particular the selection of the contact plane according to the chirality of its constituent helices, and direct observation of both right and left hands of polyolefin helices.     

Plasma fluorination of polyolefins

ESCA and contact angle measurements were used to characterize the surfaces of Polyethylene and polypropylene films exposed to SF₆, CF₄, and C₂F₆ plasmas. None of these gases polymerized in the plasma. However, all plasma treatments grafted fluorinated functionalities directly to the polymer surfaces. SF₆ plasmas graft fluorine atoms to a polyolefin surface. CF₄ plasmas also react by a mechanism dominated by fluorine atoms, but with some contribution from CF_x-radical reactions. Although C₂F₆ does not polymerize, the mechanism of grafting is still dominated by the reactions of CF_x radicals. For all gases studied, the lack of polymerization is attributed to competitive ablation and polymerization reactions occurring under conditions of ion bombardment.     

Post-polymerization functionalization of polyolefins

Polyolefins are macromolecular alkanes and include the most familiar and most commercially produced plastic, polyethylene. The low cost of these materials combined with their diverse and desirable property profiles drive such large-scale production. One property that renders polyolefins so attractive is their resistance to harsh chemical environments. However, this attribute becomes a severe limitation when attempting to chemically convert these plastics into value-added materials. Functionalization of polymers is a useful methodology for the generation of new materials with wide ranging applications, and this tutorial review describes both new and established methods for the post-polymerization modification of polyolefins.     

Catalytic degradation of polyolefins

Silica, alumina, silica-aluminas and zeolites were screened as catalysts for polyolefins degradation. The degradations were carried out at temperatures from 200°C till to 600°C under vacuum. The degradation products were analyzed using gas chromatography-mass spectrometry (GC-MS). The comparison between these products and those obtained by thermal degradation in the absence of catalyst gives us many informations about the different mechanisms of the two degradation reactions. Kinetic measurements and thermogravimetry provided further useful data for screening the catalysts, finding the best operating conditions.     

Impact resistance of hybrid glass fiber reinforced epoxy/nanoclay composite

The effect of nanoclay addition in Glass Fiber Reinforced Epoxy (GFRE) composites on impact response was studied. The epoxy nanocomposite matrix with 1.5 and 3.0 wt% loading of I.30E nanoclay was produced by high shear mixing. Hybrid GFRE nanoclay composite plates were manufactured by hand layup and hot pressing techniques using electrical grade-corrosion resistant (E-CR) glass fiber mats. The laminates were then subjected to low-velocity impact with energies between 10 and 50 J. Addition of nanoclay was found to improve peak load and stiffness of GFRE. Nanoclay loading of 1.5 wt% resulted in optimum properties, with 23% improvement in peak load and 11% increase in stiffness. A significant reduction in physical damage was also observed for hybrid nanocomposite samples as compared to GFRE. This was mainly attributed to transition in damage mechanism due to nanoclay addition. Clay agglomeration in samples with 3.0 wt% loading contributed towards limiting the improvement in impact resistance.     

Radar transparent glass fabric reinforced polyetherimide/Cloisite 30B nanocomposites

High performance radar transparent materials (RTMs) are important materials for the fabrication of radomes, nosecones, etc. of high velocity aerospace vehicles. RTMs with good mechanical performance and temperature capability are required for such applications. Toward this, fabric reinforced nano‐reinforced matrix composites (FRNCs), using reinforcing E‐glass fabric in Cloisite 30B reinforced polyetherimide (PEI) nanocomposite matrix (GNRPEI), was prepared. The properties of GNRPEI were evaluated and compared with E‐glass fabric reinforced PEI composites (GRPEI) with special reference to their radar transparent character for aerospace applications. Tensile and flexural properties along with interlaminar shear strength of GRPEI were observed to be lower than those of GNRPEI. Thermal behavior of both the composites was similar in differential scanning calorimetry and thermal gravimetric analysis. But, in dynamic mechanical analysis, an increase in storage modulus and decrease in loss tangent were observed in GNRPEI compared to GRPEI. The values of dielectric constant and loss tangent of GNRPEI were lesser than those of GRPEI, but no significant difference was observed in the values of transmission and reflection losses for both the composites at 8–12 GHz frequency. FRNCs, based on organoclay reinforced PEI matrix, hold good promise as high performance RTMs. Copyright © 2010 John Wiley & Sons, Ltd.     

Metallocene polyolefins and their blends#

Commercial copolymers of 1‐octene and ethylene: metallocene catalyzed (mLLDPE) and Ziegler‐Natta catalyzed (znLLDPE), a low density polyethylene (LDPE), and high density polyethylene (HDPE), were characterized with respect to branching, crystallization behaviour and dynamic‐mechanical properties. It was found that the crystallinity of the polymers is more influenced by the homogeneity of the short‐chain branching than by its content. The study of blends of mLLDPE and znLLDPE with LDPE and HDPE showed that the interaction between mLLDPE and LDPE is stronger than between znLLDPE and LDPE. Blends containing mLLDPE showed a composition depending improvement of the storage modulus G' which was not observed in znLLDPE/LDPE blends. The HPDE blends followed a linear mixing rule. Co‐crystallization was found mLLDPE/LDPE and partially in znLLDPE/LDPE and znLLDPE/HDPE blends, respectively.     

New reactive additives for interface modification in multicomponent polyolefin systems

New reactive additives were synthesised and used as interface modifiers in different multicomponent polyolefine systems. The synthesis was carried out in computer‐controlled reactor by means of Diels‐Alder reaction and condensation. These additives are capable of combining the benefits of dispersing and coupling agents. A part of the synthesised reactive surfactants have also synergistic effect in flame retardant systems. Their surface‐active character facilitates the reactive compounding. The undesirable transport processes of stabilisers and components of flame‐retardants in polyolefine systems could be effectively controlled by interface modification.