Materials Science Forum Vols. 730-732

Abstract: In this study the influence of nanoclay and glass fibre in the shrinkage and ejection forces in polypropylene matrix in tubular parts moulded by injection moulding were analysed. An instrumented mould was used to measure the part surface temperature and ejection forces in tubular parts. The materials used were a polypropylene homopolymer Domolen 1100L nanoclay for polyolefin nanocomposites P-802 Nanomax in percentages of 2%, 6% and 10% and a polypropylene homopolymer with content of 10% of glass fibre Domolen P1-013-V10-N and 30% of glass fibre Domolen P1-102-V30-N with 2% of nanoclay. The shrinkage and ejection forces were analysed. The results show that the incorporation of nanoclays decreases the shrinkage and ejection forces whereas glass fibre decreases the shrinkage and increase ejection forces due to the increase of the elastic modulus. The nanoclays decrease the ejection force when compared with glass fibre and pure PP. The effects of nanoclays are less pronounced than those of glass fibre. The effect of the mould temperatures on the ejection forces in the mouldings produced with the mentioned materials were also analysed. The ejection force decreases with the increase of the temperature of the mould.

Abstract: The Keggin-type TBA₄H₂[BW₁₁Mn(H₂O)O₃₉].H₂O (BW₁₁Mn) compound was isolated and characterized. The first sphere of coordination for the manganese atom was determined by EXAFS analysis. Six oxygen atoms were found in the range of 1.80-2.64 Å from the manganese. BW₁₁Mn showed to be an active, efficient and selective catalyst for cis-cyclooctene (1a) epoxidation in the presence of stoichiometric quantities of H₂O₂. After 5 h of reaction almost complete conversion was achieved (86% of conversion). Selectivity was always 100 % for the epoxide.

Abstract: Structural foams (SF) consist of a sandwich-like material composed by a cellular core and a solid skin. It is the ideal material solution for injection moulding of short production series of large size parts. The injection moulding of SF is a low pressure process, thus it is a viable alternative for light moulding tools. The right formulation of structural foams and the use of adequate processing conditions are important to optimize the performance of the plastics part. In this study the processing conditions (injection speeds and percentages of mould filling) and the amount of chemical blowing agent (CBA) added to polypropylene were assessed on injection moulding circular discs. A hybrid mould with epoxy/aluminium composite cavity was used to produce the parts. The structural foam performance was evaluated by rheological, morphological and mechanical tests.

Abstract: In the last years there have been made several studies, involving many materials, with the aim of trying to explain some physical, chemical and mechanical macroscopic properties of these materials, across the study of the free volumes at the atomic and molecular scale. The positron annihilation lifetime spectroscopy (PALS) is one of the most widely used in this type of studies, and it was here used to characterize the free volumes fraction of a commercial epoxy and trying to understand the mechanism associated with the process of moisture absorption which leads to an increase of mass and volume on this commercial epoxy.

Abstract: The glued laminated timber (glulam) mechanical properties may be evaluated through the determination of the key mechanical properties of the lamellae that compose that element. Simple bending and tension parallel to the grain tests were performed in order to assess the strength class of three glulam elements. Regarding the bending tests, 8 samples were taken from a glulam beam and assessed. Values for the resistant bending tension and both local and global modulus of elasticity were obtained. For the tension parallel to the grain tests, a total of 120 samples were assessed. The samples were divided regarding the structural element from where they were extracted as well to the type of failure mode found in the tests. The values of the lamellae properties were then used for determination of the properties of the glulam material. The data gathered from the tests was assessed statistically and concluded that the mechanical properties of the glulam elements did not fulfill the required parameters of the normative requirements.

Abstract: Adhesive joints are largely employed nowadays as a fast and effective joining process. The respective techniques for strength prediction have also improved over the years. Cohesive Zone Models (CZM’s) coupled to Finite Element Method (FEM) analyses surpass the limitations of stress and fracture criteria and allow modelling damage. CZM’s require the energy release rates in tension (G_n) and shear (G_s) and respective fracture energies in tension (G_n^c) and shear (G_s^c). Additionally, the cohesive strengths (t_n⁰ for tension and t_s⁰ for shear) must also be defined. In this work, the influence of the CZM parameters of a triangular CZM used to model a thin adhesive layer is studied, to estimate their effect on the predictions. Some conclusions were drawn for the accuracy of the simulation results by variations of each one of these parameters.

Abstract: We have employed molecular dynamics simulations to study the behavior of virtual polymeric materials under an applied uniaxial tensile load. Through computer simulations, one can obtain experimentally inaccessible information about phenomena taking place at the molecular and microscopic levels. Not only can the global material response be monitored and characterized along time, but the response of macromolecular chains can be followed independently if desired. The computer-generated materials were created by emulating the step-wise polymerization, resulting in self-avoiding chains in 3D with controlled degree of orientation along a certain axis. These materials represent a simplified model of the lamellar structure of semi-crystalline polymers, being comprised of an amorphous region surrounded by two crystalline lamellar regions. For the simulations, a series of materials were created, varying i) the lamella thickness, ii) the amorphous region thickness, iii) the preferential chain orientation, and iv) the degree of packing of the amorphous region. Simulation results indicate that the lamella thickness has the strongest influence on the mechanical properties of the lamella-amorphous structure, which is in agreement with experimental data. The other morphological parameters also affect the mechanical response, but to a smaller degree. This research follows previous simulation work on the crack formation and propagation phenomena, deformation mechanisms at the nanoscale, and the influence of the loading conditions on the material response. Computer simulations can improve the fundamental understanding about the phenomena responsible for the behavior of polymeric materials, and will eventually lead to the design of knowledge-based materials with improved properties.

Abstract: In this work the syntheses of covalently grafted Ni(II)-complexes formed with various N- or C-protected amino acid ligands (L-histidine, L-tyrosine, L-cysteine and L-cystine) inspired by the active site of the Ni-SOD enzyme are presented. Merrifield’s resin was used as support to mimic the proteomic skeleton of the enzyme. Conditions of the syntheses were altered and the structural features of the substances obtained were studied by infrared spectroscopy. It was found that the preparation of covalently anchored Ni(II)−amino acid complexes was successful in all cases. In many cases the structures of the anchored complexes and the coordinating groups substantially varied upon changing the conditions of the syntheses. The obtained materials were studied by energy dispersive X-ray fluorescence coupled to scanning electron microscope (SEM−EDX). All the covalently anchored materials displayed superoxide dismutase (SOD) activity and some proved to be exceptionally efficient in the biochemical test reaction.

Abstract: Adhesive bonding as a joining or repair method has a wide application in many industries. Repairs with bonded patches are often carried out to re-establish the stiffness at critical regions or spots of corrosion and/or fatigue cracks. Single and double-strap repairs (SS and DS, respectively) are a viable option for repairing. For the SS repairs, a patch is adhesively-bonded on one of the structure faces. SS repairs are easy to execute, but the load eccentricity leads to peel peak stresses at the overlap edges. DS repairs involve the use of two patches, one on each face of the structure. These are more efficient than SS repairs, due to the doubling of the bonding area and suppression of the transverse deflection of the adherends. Shear stresses also become more uniform as a result of smaller differential straining. The experimental and Finite Element (FE) study presented here for strength prediction and design optimization of bonded repairs includes SS and DS solutions with different values of overlap length (L_O). The examined values of L_O include 10, 20 and 30 mm. The failure strengths of the SS and DS repairs were compared with FE results by using the Abaqus^® FE software. A Cohesive Zone Model (CZM) with a triangular shape in pure tensile and shear modes, including the mixed-mode possibility for crack growth, was used to simulate fracture of the adhesive layer. A good agreement was found between the experiments and the FE simulations on the failure modes, elastic stiffness and strength of the repairs, showing the effectiveness and applicability of the proposed FE technique in predicting strength of bonded repairs. Furthermore, some optimization principles were proposed to repair structures with adhesively-bonded patches that will allow repair designers to effectively design bonded repairs.

Abstract: Metal-Organic Framework Materials MIL‑101(Cr) ([Cr₃X(H₂O)₂O(bdc)₃]∙n(H₂O), where X⁻ = F⁻ or OH⁻, n ≈ 25 and H₂bdc stands for 1,4-benzene-dicarboxylic acid] and MOF‑5(Zn) [Zn₄O(bdc)₃] were prepared by hydrothermal or solvothermal methods as well as Microwave‑Assisted Synthesis (MWAS), for which the detailed synthetic parameters were optimized. The crystal structures were confirmed by powder X-ray diffraction and the materials were further characterized by FT‑IR absorption spectroscopy. MIL‑101(Cr) and MOF‑5(Zn) showed weak catalytic activity in the oxidation of terpene, thiophene and cis-cyclooctene. Reasonable catalytic activity was observed for MOF-5(Zn) in the epoxidation of cis-cyclooctene and a 100 % of selectivity was observed for the epoxide. The structural stability of the materials was tested under the employed catalytic medium for oxidation reactions. MOF-5(Zn) revealed a remarkable structural stability at high temperature and also in the presence of high oxidant amounts.