All issues / Volume 8 (2014) / Issue 5 (May)
This is an editorial article. It has no abstract.
This paper presents an innovative and effective methodology to characterize plastic flow and failure in single point incremental forming (SPIF) of polymers that allows determining the stresses and the accumulated values of ductile damage directly from the experimental values of strain at various positions over the deformed polymer sheets. The approach traces the deformation path of material elements in conical and pyramidal SPIF parts, undergoing linear strain loading paths from beginning until failure, and is built upon the generalization of the analytical framework conditions assumed by Glover et al.  to the pressure-sensitive yield surfaces of polymers under incompressible, non-associated, plastic flow. Experimentation in conventional and multi-stage SPIF of Polyvinylchloride (PVC) sheets confirms the effectiveness of the proposed methodology and demonstrates that standard non-coupled damage models currently utilized in sheet metal forming are inapplicable to describe failure in polymers. Instead fracture forming limit lines (FFL’s) should be employed.
A micro-Raman study is carried out to investigate the influence of the filler on the curing process of bisphenol A diglycidyl ether (DGEBA)-based epoxy matrix composites. The composites are cured (14 h at 393 K) with an anhydride (methyl tetrahydro phthalic anhydride, MTHPA, 100:90 pbw), catalyzed with a tertiary amine (0.7 pbw) and filled with a 30% volume of Cu particles of approximately 75 µm in diameter. The experimental results are compared with those obtained for the same epoxy resin unfilled and for the same composite with Cu filler but not catalyzed. The micro-Raman experimental technique is used to search for information on the curing process in different regions of the matrix, near to and far from the copper filler, taking into account the results of differential-scanning-calorimetry measurements performed on the same composites. The results provide information on the influence of the copper filler on the curing process of the epoxy matrix. Differences were observed in the peaks associated with the epoxy ring and the ester group as a function of the distance to the nearest copper particle, but no differences were observed between the different composites.
The aim of the present work is to assemble extracellular matrix components onto poly (L-lactic acid) (PLLA) films using layer-by-layer (LBL) depositing method to enhance the cell-material interaction. To introduce charges onto the hydrophobic and neutral PLLA surface so that the electronic assembly can be processed, poly (ethylene imine) (PEI) was covalently bonded to modify the PLLA films. Positively charged collagen I (Col I) was then deposited onto the aminolyzed PLLA film surface in a LBL assembly manner using hyaluronic acid (HA) as a negatively charged polyelectrolyte. The PEI modification efficiency was monitored via X-ray photoelectron spectroscopy (XPS) measurements. The results of Surface Plasmon Resonance (SPR) and Water contact angle (WCA) monitoring the LBL assemble process presented that the HA/Col I deposited alternately onto the PLLA surface. The surface topography of the films was observed by Atomic force microscope (AFM). In vitro osteoblast culture found that the presence of Col I layer greatly improved the cytocompatibility of the PLLA films in terms of cell viability, cell proliferation and Alkaline Phosphatase (ALP) expression. Furthermore, osteoblast extensions were found to be directed by contact guidance of the aligned Col I fibrils. Thus, these very flexible systems may allow broad applications for improve the bioactivity of polymeric materials, which might be a potential application for bone tissue engineering.
The objective of the present work is to enhancing the toughness and minimizing the CTE of a special class of bisphenol E cyanate ester (BECy) resin by blending it with a thermoplastic toughening agent. Poly(ether sulfone) was chosen as a high temperature resistant thermoplastic resin to enhance the thermo-mechanical properties of BECy. The influence of poly(ether sulfone)/BECy blend composition on the morphology and phase behavior was studied using scanning electron microscopy and dynamic mechanical analysis. The mechanical properties of the blends were evaluated by flexural tests, which demonstrated significant enhancement in the material’s toughness with an increase in PES concentration from 0 to 15 wt%. The coefficient of thermal expansion of pure BECy was reduced from 61 to 48 ppm/°C in the blends with PES, emphasizing the multi-functional benefits of PES as a toughening agent in BECy.
The microstructures of Estane 5703 aged at 70°C in dry and wet air have been studied by small-angle neutron scattering. The samples were swollen in deuterated toluene for enhancing the contrast. The scattering data show the characteristic domain structure of polyurethanes consisting of soft and hard segments. Debye-Anderson-Brumberger function used with hard sphere structure factor, and the Teubner-Strey model are used to analyze the two-phase domain structure of the polymer. The combined effects of temperature and humidity have a strong disruption effect on the microstructures of Estane. For the sample aged at 70°C in wet air for 1 month, the domain size, described by the correlation length, increases from 2.3 to 3.8 nm and their distance, expressed by hard-sphere interaction radius, increases from 8.4 to 10.6 nm. The structure development is attributed to degradation of polymer chains as revealed by gel permeation chromatography. The hydrolysis of ester links on polymer backbone at 70°C in the presence of water humidity is the main reason for the changes of the microstructure. These findings can contribute to developing predictive models for the safety, performance, and lifetime of polyurethanes.
The aim of this work was to investigate the suitability of electrospinning for biodrug delivery and to develop an electrospinning-based method to produce vaginal drug delivery systems. Lactobacillus acidophilus bacteria were encapsulated into nanofibers of three different polymers (polyvinyl alcohol and polyvinylpyrrolidone with two different molar masses). Shelf life of the bacteria could be enhanced by the exclusion of water and by preparing a solid dosage form, which is an advantageous and patient-friendly way of administration. The formulations were stored at –20, 7 and 25°C, respectively. Viability testing showed that the nanofibers can provide long term stability for huge amounts of living bacteria if they are kept at (or below) 7°C. Furthermore, all kinds of nanowebs prepared in this work dissolved instantly when they got in contact with water, thus the developed biohybrid nanowebs can provide new potential ways for curing bacterial vaginosis.
Dispersing hydrophilic nanoparticles in hydrophobic polymers: HDPE/ZnO nanocomposites by a novel template-based approach
M. Salzano de Luna, M. Galizia, J. Wojnarowicz, R. Rosa, W. Lojkowski, C. Leonelli, D. Acierno, G. Filippone
Vol. 8., No.5., Pages 362-372, 2014
Vol. 8., No.5., Pages 362-372, 2014
The efficiency of a novel template-based approach for the dispersion of hydrophilic nanoparticles within hydrophobic polymer matrices is investigated. The procedure envisages the permeation of a well dispersed nanoparticle suspension inside a micro-porous matrix, obtained through selective extraction of a sacrificial phase from a finely interpenetrated co-continuous polymer blend. Specifically, a blend of high density polyethylene (HDPE) and polyethylene oxide (PEO) at 50/50 wt% is prepared by melt mixing. The addition of small amounts of organo-clay promotes the necessary refinement of the blend morphology. Once removed the PEO, the micro-porous HDPE matrix is dipped in a colloidal suspension of zinc oxide nanoparticles which exhibits low interfacial tension with HDPE. A system prepared by traditional melt mixing is used as reference. Melt- and solid-state viscoelastic measurements reveal a good quality of the filler dispersion despite the uneven distribution on micro-scale. The latter can be capitalized to minimize the filler content to attain a certain improvement of the material properties or to design nano-structured polymer composites.