Band 35, Heft 3

This paper presents the effect of process parameters of twin screw extruder and addition of Cloisite-15A on mechanical, thermal and moisture barrier properties of epoxy/Cloisite-15A nanocomposites. Four lobed kneading blocks were used the in shearing zone of the extruder, based on their effectiveness in dispersing nanofillers in epoxy. Screw speeds from 100 min −1 to 400 min −1 , number of passes up to 15, temperature from 5°C to 80°C and Cloisite-15A contents from 1 wt.% to 2.5 wt.% were considered for designing the L 12 Orthogonal Array. Improvements in tensile strength, compression strength, flexural strength, impact strength, hardness and moisture diffusivity in the nanocomposites were 11.89%, 20.06%, 27.73%, 37.26%, 25.48% and 56.22% respectively, when compared to neat epoxy. The improvements were achieved for screw speed of 400 min –1 , 5 passes through the extruder, processing temperature of 5°C and 2 wt.% of Cloisite-15A. Dispersion of Cloisite-15A in epoxy was studied by XRD, SEM and TEM. Thermal stability and moisture barrier properties were superior in the nanocomposites.

This study experimentally investigated the effect of different molecular weights of Poly vinyl acetate (PVAc) on electrospinning ability of PVAc/DMAC sol-gels. The influences of polymer solution concentration and electrospinning process parameters (needle tip to collector distance, flow rate, and applied voltage) on the mean diameters of electrospun PVAc nanofibers were examined by design of the experiments based on the Taguchi method. Three levels were considered for each process factor as inputs for the Taguchi DoE technique. To characterize and optimize the mentioned parameters, Taguchi's L9 orthogonal design (four parameters, three levels) was used. The “smaller-the-better” approach was used to utilize the optimum production conditions based on the signal-to-noise (S/N) ratios. The results indicated that the polymer solution concentration was the most important parameter on the mean diameter of the nanofibers. The minimum nanofiber diameter at the optimum conditions was measured about 52 nm. In conclusion, the Taguchi DoE method was identified as an efficient technique to characterize and optimize the electrospinning process parameters to increase the robustness of nanofiber fabrication.

In this study, polyphenylene sulfide (PPS) was introduced in polyphenylene ether (PPE) blend to improve the processability of PPE and to secure the flame retardancy of the blend without deteriorating physical properties. Through the study of the binary blend of PPE/PPS, it was found that the shear thinning behavior and the external lubrication effect of PPS can improve the processability of PPE. Thermal analysis of the blend showed that the glass transition temperature of the PPS component decreases by the plasticization while that of the PPE component increases by the anti-plasticization effect. The modulus of the binary blend increased with the PPS content, and the tensile strength decreased but followed the additive rule. The change in tensile properties can be explained by the synergy effect of partial miscibility between PPE and PPS due to structural similarity, and non-isotropic morphology formation. Impact strength increased sharply in PPE60 due to the mechanical grafting effect by co-continuous phase formation. In the ternary blend with SEBS-MAH applied to PPE60, the impact strength steep increased at a content of 10 wt% or more due to the dramatic morphology change based on the compatibilization effect. Flame retardancy of V0 was also observed in all compositions where SEBS-MAH was applied within 20 phr.

The process of dispersing filler in polymer matrix is vital to the behavior of polymer composites. The current study involves understanding the extent of dispersion of filler by only varying the nature of mixing during the process. Identical polymer composite materials are processed via two different kinds of mixing sections on the screw in a twin-screw extruder, differing in the type and amount of stress they impose on the filler agglomerate. An aggressive (90 0 ) Kneading Block (KB) mixing section is compared with recently developed Extensional Mixing Elements (EMEs), which impart extension dominated mixing while KB imparts shear dominated mixing. Various EME geometries of different levels of aggressiveness were computationally studied and validated. Composites obtained from KB are compared with composites processed using five different EME geometries. Three composites of Polypropylene (PP) filled with carbon black, graphene nano platelets and carbon nanotubes were studied independently. Composites processed through EMEs display about an order of magnitude better dispersion of filler agglomerate over the composites processed through KB. In addition, enhanced modulus and yield stress is observed for composites processed through EMEs. An improvement of 63% to 266% in the strain achieved for EME processed composites is seen under biaxial film stretching.

It is generally accepted that the benefit of anisotropic nanofiller addition is strongly dependent on the state of the dispersion of these fillers in a polymer matrix. In this paper the influence of melt-compounding conditions on the dispersion of a needle-like clay, i. e. sepiolite, in poly(∊-caprolactone) (PCL) is investigated. The crystallisation behavior as well as the rheological and mechanical properties of PCL/sepiolite nanocomposites with filler contents up to 5 wt.% are studied. By changing the screw speed during melt-mixing in a micro-compounder, the state of dispersion was varied, with the higher speed leading to better dispersion and breakdown of the sepiolite agglomerates or bundles. Rheometry showed that better dispersed nanocomposites displayed an increase in viscosity due to network formation at slightly higher filler loadings. Likewise, better dispersed composites showed a modest increase in crystallisation temperature at low filler content, accompanied by a decrease in both nucleation efficiency and degree of crystallisation at higher loadings. Better dispersed nanocomposite systems also showed superior mechanical properties, particularly at higher filler loadings. However, overall the reinforcing efficiency of sepiolite in all nanocomposites was relatively low. This was mainly a consequence of the relatively low filler aspect ratio and the simultaneous breakup of sepiolite needles together with a breakdown of bundles during compounding.

This article presents comparative experimental and numerical studies to investigate the deformation and contact force of orthotropic microplates under indentation test. A simple model is developed to obtain the 3D homogenized elastic properties of orthotropic materials. In the FE simulation, the microplate is assumed to be a fully elastic orthotropic composite, and the indenter is a rigid body. Experimental indentation test is performed to obtain load-displacement curve, indentation profile, and maximum indentation depth. The numerical studies are performed to investigate the effect of indenter radius, material orthotropy, and microplate thickness on deformation of microplate under indentation load and contact pressure. The numerical model is applied to simulate two different load conditions: microplate rested on a fully supported rigid fixture, and microplate rested on a hollow support rigid fixture with circular cut-out. Numerical and experimental studies achieve excellent agreement and good correlation proving the validity of the proposed homogenization model. These parametric studies proved that the indentation behavior of orthotropic laminated structures is material independent and it depends greatly on the plate thickness.

Thermosetting polyurethane foams are nowadays produced with typical bubble size, d > 150 μm, with plenty of room for improvement towards the cellular structure refinement, to gain, among others, in the thermal insulation performances. We herein report a first example of a microcellular thermosetting polyurethane foam, i. e. with bubble size below 5 μm, produced via the gas foaming technology. In particular, high-pressure CO 2 , N 2 and their mixtures were utilized as blowing agents: solubilized separately into the polymer precursors, they were brought into a supersaturated state by a pressure reduction to induce the bubble nucleation and growth. To achieve microcellular foams, we made use of a novel two-stage pressure reduction program, concurrent to the polymer curing. The first stage is a pressure quench O (10 –2 s) from the saturation pressure to an intermediate pressure to induce the nucleation of a large amount of dense bubbles. The second stage is a slow O (10 2 s) further pressure decrease to ambient pressure, allowing for a slow bubble growth, designed to reach ambient pressure exactly when the curing reached completion.

Plantain (Musa paradisiaca) is a widely cultivated plant in Nigeria which generates lots of residues (such as its peels) during its consumption. This study investigated the tensile, microstructural and moisture absorption properties of plantain peel reinforced polystyrene composites. The filler composition was varied between 0 wt% and 40 wt% and all analyses were done as per ASTM standards. The force at break and Young's modulus increased with increasing filler content and had maximum values of 405 N and 380 MPa respectively. The elongation at break point of plantain peel powder reinforced bio-composite reduced with increase in filler content, indicating that the biomass fillers led to a reduction in the deformability of the composites due to a poor transfer of stress at the weak fiber-plastic interphase. It was furthermore observed that composites with higher filler content were more susceptible to moisture diffusivity due to the hydrophilic nature of the filler powder. Microstructural analysis revealed that a more uniform distribution of the plantain fiber occurs at 40% fiber content compared to those of higher filler content.