Ab Anne Spoelstra

The rubber particle size to control the properties-processing balance of thermoplastic/cross-linked elastomer blends

The influence of the number-averaged rubber particle size (dn) on the mechanical and rheological properties of thermoplastic/cross-linked elastomer blends was studied, with the focus on thermoplastic vulcanizates (TPVs) based on poly(propylene) (PP) and ethylene-propylene-diene (EPDM) rubber. Time-resolved small-angle X-ray scattering measurements revealed that the criteria to obtain tough behavior are very different for TPVs than for traditional rubber-toughened thermoplastics, since the deformation mechanism of TPVs under tensile conditions is dominated by yielding of the semi-crystalline, thermoplastic matrix without the occurrence of matrix crazing and internal rubber cavitation. The formation of interlamellar voids, as occurs in the unfilled thermoplastic during deformation, is more effectively suppressed with decreasing dn, which leads to a significant enhancement of the ultimate tensile properties. Additionally, the decrease in dn leads to an enhanced elastic recovery, but also increases the melt viscosity. These results demonstrate that dn is an important parameter to control the balance between the mechanical properties and the melt processability of blends based on thermoplastics and cross-linked elastomers.

Role of superheated water in the dissolution and perturbation of hydrogen bonding in the crystalline lattice of polyamide 4,6

Here, we demonstrate that water, in the superheated state, is a solvent for polyamide 4,6 (PA4,6) and that the water molecules can strongly influence hydrogen bonding. In the presence of superheated water, the melting temperature of PA4,6 can be suppressed by nearly 100 degrees C. The depression in the melting temperature follows the Flory-Huggins principle. The instantaneous dissolution of the polymer hardly influences the molar mass of the polymer. However, if the polymer is retained in solution above the dissolution temperature for more than 10 min, hydrolysis occurs. These findings suggest that the dissolution of the aliphatic polymer in superheated water is mainly a physical process as opposed to a chemical process. Time resolved X-ray studies show that the dissolution occurs prior to the Brill transition temperature, as reported earlier. Crystals grown from the water solution show a lath-like morphology with interchain and intersheet distances that are similar to the distances obtained for crystals grown from other known solvents. Electron diffraction further confirmed that the crystals grown from superheated water are single crystals, where the chains are perpendicular to the ab-plane. SAXS performed on dried sedimented water grown single crystals showed a lamellar thickness of 6 nm. The lamellar thickness is in accordance with other reported studies on PA4,6, confirming that the single crystals incorporate four repeat units between re-entrant folds with an amide group incorporated in the tight fold. Solid state NMR studies performed on mats of these single crystals showed two different mobilities of the proton associated with the amide groups: a higher mobility linked to the amide protons in the fold and a reduced mobility of the hydrogen bonded amide protons within the crystal. Additionally, the solid state NMR studies on the dried water crystallized single crystals show the presence of water molecule(s) in the vicinity of the amide groups. This was confirmed by infrared studies that conclusively demonstrated the appearance of two new bands arising due to the binding of a water molecule in the vicinity of the amide group (i.e., NH3(+) and COO(-) bands that disappear upon heating at approximately 200 degrees C). Additionally, DSC traces of the water crystallized PA4,6 show an exothermic event in the same temperature region (i.e., in the vicinity of the Brill transition temperature, where the bound water exits from the lattice). Furthermore, this event was corroborated by TGA data.

Structure–property relationships of reactively compatibilized PHB/EVA/starch blends

A method is addressed to prepare poly(hydroxybutyrate)/poly(ethylene-co-vinyl acetate)/starch (PHB/EVA/starch) blends with fine dispersion of starch, i.e. by an in situ compatibilization in the presence of maleic anhydride (MA) and peroxide. The starch particle size is reduced from hundreds-μm to sub-μm after the compatibilization accompanied by an improvement in interfacial adhesion. Meanwhile, starch-in-EVA-type morphology is observed in the blends. The EVA and starch gradually changed into a (partially) co-continuous phase with increasing MA content. Consequently, toughness of the blends was improved as evidenced by an increase in elongation at break and tensile-fracture energy (work). Cavitation, fibrillation and matrix yielding are regarded as the toughening mechanism for the compatibilized blends. In addition, the Tg of the EVA phase is dependent on its phase morphology in the blends while the thermal behavior of the PHB was only slightly affected by the compatibilization.

An ATRP-based approach towards water-borne anisotropic polymer–Gibbsite nanocomposites

Polymer–Gibbsite composite latex particles were synthesised via an atom transfer radical polymerisation (ATRP) based approach. A random ATRP cooligomer, consisting of acrylic acid and butyl acrylate units, was synthesized using ATRP. This cooligomer was used as a stabiliser for the Gibbsite platelets and served as a macroinitiator for copper-mediated starved-feed emulsion polymerisation. Using a hydrophobic ligand for Cu2+ and optimising the feeding profile of ascorbic acid and the [ascorbic acid]/[Cu2+] ratio, successful Activator ReGenerated by Electron Transfer (ARGET) ATRP emulsion polymerisation was conducted in a controlled way, using only the anionic ATRP cooligomer as a surfactant. Cryo-TEM characterisation revealed a “muffin-like” morphology of the resulting composite latex particles, which was not affected by monomer feed composition and feeding profile.

Fabrication of PEDOT–OTS-patterned ITO substrates

The fabrication of a poly(3,4-ethylenedioxythiophene) (PEDOT) pattern is demonstrated. As template, an n-octadecyltrichlorosilane (OTS) monolayer self-assembled on indium tin oxide (ITO) was structured by UV–ozone photolithography, resulting in an ITO–OTS patterned surface. The conducting properties of the ITO were utilized for the selective electropolymerization of 3,4-ethylenedioxythiophene (EDOT), whereby the electropolymerization was inhibited by the insulating OTS. Differently sized PEDOT–OTS patterns were obtained. The electronic properties of the patterns were finally evaluated in a test OLED device.

Characterization of the morphology of co-extruded, thermoplastic/rubber multi-layer tapes.

Tapes with alternating semi-crystalline thermoplastic/rubber layers with thicknesses varying from 100 nm up to several microm were prepared by multi-layer co-extrusion. The variation in layer thickness was obtained by varying the thermoplastic/rubber feed ratio. A systematic study on the use of various microscopy techniques to visualize the morphology of the layered systems is presented. The relatively large length scales and the sample preparation make optical microscopy (OM) unsuitable to study the morphology of the multi-layer tapes. Although excellent contrast between the thermoplastic and rubber layers can be obtained, the usually applied, relatively large magnifications limit the use of transmission electron microscopy (TEM) and atomic force microscopy (AFM) to small sample areas. The large range of applicable magnifications makes scanning electron microscopy (SEM) the most suitable technique to study the morphology of the multi-layer tapes. The sample preparation for SEM with a secondary electron (SE) detector is often based on the removal of one of the components, which may induce changes in the morphology. SEM with a back-scattered electron (BSE) detector is a very convenient method to study the morphology over a wide range of length scales, where the contrast between the different layers can be enhanced by chemical staining. Finally, the nucleation behavior (homogeneous versus heterogeneous) of the semi-crystalline layers, as probed by differential scanning calorimetry (DSC), provides valuable information on the layered morphology. The use of relatively straightforward DSC measurements shows a clear advantage with respect to the discussed microscopy techniques, since no sample preparation is required and relatively large samples can be studied, which are more representative for the bulk.

Rapid, direct fabrication of antireflection-coated microlens arrays by photoembossing

Photoembossing is a rapid, low cost process to create surface relief structures in polymer thin films via a reaction/diffusion mechanism. It is demonstrated that this technique can be used to create a microlens array of which the focal length can be easily controlled by tuning the processing parameters. In addition, the technique is shown to be particularly interesting since it does not require any physical contact during the development of the microlens array. Additional coatings (e.g., a solution-processable antireflection coating) can therefore be applied prior to the development of the microlens array when the film is still flat. This stimulates the formation of films with a homogeneous thickness distribution and obviates the use of further postprocessing steps.

Solid-state drawing of post-consumer isotactic poly(propylene): Effect of melt filtration and carbon black on structural and mechanical properties

Post-consumer plastic waste obtained via mechanical recycling is usually applied in thick-walled products, because of the low mechanical strength due to the presence of contaminants. In fact, sorted post-consumer isotactic poly(propylene) (i-PP) can be considered as a blend of 95% i-PP and 5% poly(ethylene), with traces of poly(ethylene terephthalate) (PET). By applying a treatment such as solid-state drawing (SSD) after melt extrusion, the polymer chains can be oriented in one direction, thereby improving the stiffness and tensile strength. In this research, molecular processes such as crystal break-up and chain orientation of these complex blends were monitored as a function of draw ratio. The melt filter mesh size - used to exclude rigid PET particles - and the addition of carbon black (CB) - often added for coloration in the recycling industry - were varied to investigate their influence on the SSD process. This research shows that despite the blend complexity, the molecular processes during SSD compare to virgin i-PP and that similar draw ratios can be obtained (λmax=20), albeit at reduced stiffness and strength as a result of the foreign polymers present in post-consumer i-PP. It is observed that the process stability improves with decreasing mesh size and that higher draw ratios can be obtained. The addition of carbon black, which resides in the dispersed PE phase, also stabilizes the SSD process. Compared to isotropic post-consumer i-PP, the stiffness can be improved by a factor 10 to over 11GPa, while the tensile strength can be improved by a factor 15-385MPa, which is approx. 70% of the maximum tensile strength achieved for virgin i-PP.

Encapsulation of unmodified Gibbsite via conventional emulsion polymerisation using charged co-oligomers

Gibbsite platelets were successfully encapsulated via starved-feed conventional emulsion polymerisation using anionic co-oligomers without the need for any surface modification of the platelets. Charged co-oligomers, consisting of butyl acrylate and acrylic acid units, were synthesized using atom transfer radical polymerisation (ATRP) and used as stabilisers for the initial Gibbsite platelets and the formed latex particles. Optimisation of co-oligomer concentration resulted in efficient encapsulation where every latex particle contained a Gibbsite platelet. Cryo-TEM characterisation showed the Gibbsite platelet completely covered with a polymer layer and this morphology was not affected by the investigated co-oligomer composition or chain length.

Rheology and Rheometry For Highly Filled Reactive Materials

The modeling and experimental investigation of the flow of highly filled reactive materials is studied. For significant numerical simulations it is of decisive importance that the material considered is characterized for all constitutive equations, although experimental problems still exists. The most important constitutive equation is the rheological equation for the stress tensor. For highly filled reactive materials, the usual characterization techniques fail. A new characterization method is proposed which circumvents these problems. In this method complex flows are encountred and differences between numerical and experimental results are used to adjust the parameter values and/or the constitutive model.