pinecone/core-2020-05-10-deduplication huggingface dataset:
Spherical calcium phosphate nanoparticle fillers allow polymer processing of bone fixation devices with high bioactivity

Treatment of bone defects generally requires a fixation device. Biodegradable implants can often prevent second operations in contrast to metallic implants that are surgically removed after healing. In this study, we investigate the preparation of a bone fixation device with additional bioactivity by adding nanoparticulate amorphous tricalcium phosphate (ATCP) to improve bonding to bone. Medically approved poly(lactide-co-glycolide) (PLGA) and spherical (ATCP) nanoparticles were blended directly or through a two-step approach, where ATCP was first dispersed in PLGA by solvent casting, extruded and hot pressed producing blocks and bone screws. The latter route yielded good particle dispersion while blending alone led to inhomogeneous mixtures. Samples were immersed in simulated body fluid and showed rapid formation of surface hydroxyapatite layers (examined by X-ray diffraction and scanning electron microscopy) already after 3 days, thus confirming very high bioactivity. Polymer degradation during processing and upon simulated implantation conditions was followed by gel permeation chromatography. The elevated temperature during extrusion was the strongest single factor contributing to PLGA degradation. Screws could be machined out of extruded cylinders and demonstrated the ability to process PLGA/ATCP 90/10 composites with regular workshop tools. These properties suggest the use of such composites as improved, bioactive, and degradable bone fixation systems particularly in oral and maxillofacial surgery. POLYM. ENG. SCI., 50:952-960, 2010. (C) 2009 Society of Plastics Engineer
Origin of the Bubble Defect in the Extrusion Coating Process

International audienceDuring the extrusion coating process, a polymer film is extruded through a flat die, stretched in air, then coated on a substrate (steel sheet in our case) in a laminator consisting of a chill roll and a flexible pressure roll. The nip, i.e., the area formed by the contact between the pressure and the chill rolls, constitutes the very heart of the extrusion coating process. Indeed, in this region, some of the most critical properties, such as adhesion, barrier properties, optical properties, are achieved. The thermomechanical analysis of Sollogoub et al., Polym. Eng. Sci., 48, 1634 (2008), was used to study the origin of the bubble defect appearing during the extrusion coating process. First, we investigate the influence of process parameters on the bubble defect. Then, we compute the thermomechanical parameters of the process, and finally, we derive a realistic bubble defect appearance criterion. POLYM. ENG. SCI., 00:000-000, 2010. ª2010 Society of Plastics Engineer
3D Model for Powder Compact Densification in Rotational Molding

During rotational molding, a loosely packed, low-density powder compact transforms into a fully densified polymer part. This transformation is a consequence of particles sintering. Powder compact density evolution of the polymer powder is measured experimentally. Obtained results show that the powder densification process consists of two stages, and its mechanism during these two stages is not the same. During the first stage, densification occurs by grains coalescence, and air between the grains escape by open pores between particles. These open pores close in time by particles coalescence progress, and remaining air entrapped in polymer melt becomes air bubbles. Surface tension, viscosity, grains size, and temperature are the controlling parameters during first stage. A three-dimensional model is proposed for the densification of polymer powder during first stage. Second stage starts after bubble forming. Diffusion is the controlling phenomena during this stage. A diffusion-based model is used for the second stage of densification. By comparing with the other models, proposed model exhibits several advantages: it is proposed in three-dimensional and takes into account the nature of layer-by-layer powder densification. Model verification by experimental data obtained for densification of two different polymers shows a close agreement between model prediction and experiments
Investigation of precipitated calcium carbonate as a processing aid and impact modifier in poly(vinyl chloride)

This article was published in the journal, Polymer Engineering and Science [© Society of Plastics Engineers] and the definitive version is available at: http://dx.doi.org/10.1002/pen.23191The effect of ultra-fine precipitated calcium carbonate (PCC), with a primary particle size of 50 nm, on the fusion behavior and mechanical properties of Ca/Zn stabilized poly(vinyl chloride) PVC has been investigated. The optimum concentration of PCC was determined and, in addition, experimental design was used to examine possible synergies between PCC and two important additives in an unplasticized PVC (PVC-U) formulation: namely, the processing aid and impact modifier. Dry blends were extruded and tested by differential scanning calorimetry, tensile testing, and Charpy impact testing. The results confirm that ultrafine PCC can give rise to large improvements in single notch impact strengths. Control values of 8 kJ/m were increased to 79 kJ/m through the addition of ultra-fine PCC. There was also found to be a significant increase in fusion levels but no effect on the tensile strength of the samples. It is concluded that PCC behaves as both a processing aid and impact modifier in PVC-U formulations, and the reasons for this are discussed
Experimental analyses of the poly(vinyl chloride) foams' mechanical anisotropic behavior

Assessing a full set of mechanical properties is a rather complicate task in the case of foams, especially if material models must be calibrated with these results. Many issues, for example anisotropy and heterogeneity, influence the mechanical behavior. This article shows through experimental analyses how the microstructure affects different experimental setups and it also quantifies the degree of anisotropy of a poly(vinyl chloride) foam. Monotonic and cyclic experimental tests were carried out using standard compression specimens and non-standard tensile specimens. Results are complemented and compared with the aid of a digital image correlation technique and scanning electron microscopy analyses. Mechanical properties (e.g., elastic and plastic Poisson's ratios) are evaluated for compression and tensile tests, for two different material directions (normal and in-plane). The material is found to be transversely isotropic. Differences in the results of the mechanical properties can be as high as 100%, or even more depending on the technique used and the loading direction. Also, the experimental analyses show how the material's microstructure behavior, like the evolution of the herein identified yield fronts and a spring back phenomenon, can influence the phenomenological response and the failure mechanisms as well as the hardening curves. POLYM. ENG. SCI., 52:2654-2663, 2012. (C) 2012 Society of Plastics EngineersNational Council for Research and Development (CNPq)National Council for Research and Development (CNPq) [133595/2008-0]Sao Paulo Research Foundation (FAPESP) [2009/00544-5]Sao Paulo Research Foundation (FAPESP
Poly-Left-Lactic Acid tubular scaffolds via Diffusion Induced Phase Separation (DIPS): control of morphology

In this work, tubular poly-left-lactic acid scaffolds for\ud
vascular tissue engineering applications were produced\ud
by an innovative two-step method. The scaffolds\ud
were obtained by performing a dip-coating around a\ud
nylon fiber, followed by a diffusion induced phase separation\ud
process. Morphological analysis revealed that\ud
the internal lumen of the as-obtained scaffold is equal\ud
to the diameter of the fiber utilized; the internal surface\ud
is homogeneous with micropores 1–2 lm large. Moreover,\ud
a porous open structure was detected across the\ud
thickness of the walls of the scaffold. An accurate\ud
analysis of the preparation process revealed that it is\ud
possible to tune up the morphology of the scaffold\ud
(wall thickness, porosity, and average pore dimension),\ud
simply by varying some experimental parameters. Preliminary\ud
in vitro cell culture tests were carried out\ud
inside the scaffold. The results showed that cells are\ud
able to grow within the internal surface of the scaffolds\ud
and after 3 weeks they begin to form a ‘‘primordial’’\ud
vessel-like structure. Modeling predictions of the dipcoating\ud
process display always an underestimate of\ud
experimental data (dependence of wall thickness upon\ud
extraction rate)
Uni- and biaxial impact behavior of double-gated nanoclay-reinforced polypropylene injection moldings

Polypopylene/nanoclay three-dimensional parts were
produced without intermediate steps by direct injection
molding to explore the influence of flow features and
nanoclay incorporation in their impact performance.
The nanocomposite was obtained by direct compounding
of commercial PP with nanoclay masterbatch. The
as-molded morphology was analyzed by X-ray and
TEM analyses in terms of skin-core structure and
nanoclay particle dispersion. The nanoclay particles
induced the reduction of b-form spherulites, a known
toughener. The impact behavior was assessed in tensile
and biaxial modes. The PP nanocomposite molding
toughness was practically unaffected by the processing
melt temperature and flow rate. Conversely the
nanoclay presence is influent in the impact performance.
Under biaxial stress impact, the regions close to
weld lines are tougher than the bulk and the fracture
develops with main crack paths along the flow direction
and the weld line. Cracking along the weld line
results from less macromolecular interpenetration and
chain entanglement, and unfavorable nanoparticle orientation.
It seems that a failure mechanism which
involves nanoclay delamination and multiple matrix
crazing explains the toughening of PP in the directions
where the nanoparticle orientation with respect to
loading is adequate.Contract grant sponsors: CONICET, ANPCyT from Argentina, MINCyT (Argentina) - FCT (Portugal), Universities Nacional de Mar del Plata and Minho
Methods for quantifying the stable sintering region in laser sintered polyamide-12

This is the peer reviewed version of the following article: VASQUEZ, M., HAWORTH, B. and HOPKINSON, N., 2013. Methods for quantifying the stable sintering region in laser sintered polyamide-12. Polymer Engineering and Science, 53 (6), pp. 1230 - 1240, which has been published in final form at http://dx.doi.org/10.1002/pen.23386 .  This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.Manufacturing complex parts by the laser sintering process requires a minimum amount of energy input for consolidation of polymer particles to occur; however too much energy can result in a decline in mechanical properties. This decrease is thought to be the result of polymer chain degradation. A stable sintering region (SSR) has been proposed to describe the optimum temperature range for successful laser sintering. This article will aim to quantify the SSR for polyamide-12 by using thermogravimetric analysis (TGA) to provide a framework for identifying key laser sintering processing parameters. Weight loss with respect to temperature is the main measurement output of the TGA procedure. However, the precise temperature and thermal history of a material is difficult to quantify during the laser sintering process; instead an energy input approach has been developed. A degradation energy was calculated from the TGA data and was used in conjunction with a laser sintering formula called energy melt ratio to prescribe build parameters for laser sintered parts. The mechanical properties of these parts illustrated the effect of degradation at various levels of energy input. Implications for this work include optimizing the material selection process for polymer laser sintering materials beyond polyamide-12. © 2012 Society of Plastics Engineers
Effect of Prior Photodegradation on the Biodegradation of Polypropylene/Poly(3-hydroxybutyrate) Blends

In this work, the effect of blend composition and previous\ud
photodegradation on the biodegradation of polypropylene/\ud
poly(3-hydroxybutyrate) (PP/PHB) blends\ud
was studied. The individual polymers and blends with\ud
or without the addition of poly(ethylene-co-methyl acrylate-\ud
co-glycidyl methacrylate) [P(E-MA-GMA)] as a\ud
compatibilizer (in the case of 80/20 blend) were\ud
exposed to UV light for 4 weeks and their biodegradation\ud
was evaluated. The biodegradation of PHB phase\ud
within the blends was hindered as PHB was the dispersed\ud
phase and PP fibrous particles were observed\ud
at the surface of the blend samples after biodegradation.\ud
Previous photodegradation lessened PHB biodegradation\ud
but enhanced the biodegradation of PP and\ud
the blends within the biodegradation time studied.\ud
Photodegradation resulted in cracks at the surface of\ud
PP and the blends, which probably facilitated the biotic\ud
reactions due to an easier access of the enzymes to\ud
deeper polymer layers. It also resulted in a decrease of\ud
molecular weight of PP phase and formation of carbonyl\ud
and hydroxyl groups which were consumed during\ud
biodegradation. Size exclusion chromatography\ud
analysis revealed that only the short chains of PP were\ud
consumed during biodegradation.Capes, FAPESP, CNPq for financial support and Kleber Vaccioli for performing the respirometry experiments
Preparation and characterization of high performance exfoliated montmorillonite/silicone rubber nanocomposites with enhanced mechanical properties

This is the peer reviewed version of the following article: Polymer Engineering and Science, which has been published in final form at http://dx.doi.org/10.1002/pen.23528. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Highly exfoliated and intercalated silicone rubber (SR) nanocomposites based on natural montmorillonite (Cloisite Na+) and organically modified montmorillonite (Cloisite 30B and Cloisite 20A) were successfully prepared by melt-mixing technique. Dispersion of the nanoclays in the rubber nanocomposites was subsequently investigated. As indicated by the X-ray diffraction (XRD) analysis, intercalation and exfoliation of the clay particles in the nanocomposites was achieved at less than 8 parts per hundred (phr) rubber by weight, irrespective of the initial interlayer spacing of the nanoclay particles. Both Cloisite Na+ and Cloisite 30B were spontaneously transformed into exfoliated microstructures during the vulcanisation stage. Overall, the use of the nanoclays in silicone rubber improved the Young’s modulus, tensile strength and elongation at break by more than 50% as compared to the control rubber. In addition, this work provided a fresh insight into the way intercalated and exfoliated morphologies affect mechanical properties of silicone rubber nanocomposites. It was shown that the exfoliated Cloisite Na+ yielded outstanding mechanical properties with low hysteresis at the same loading of the exfoliated Cloisite 30B and intercalated Cloisite 20A organoclays. As expected, the formation of crosslinks affected the mechanical properties of the rubber vulcanizate significantly
Talc as a nucleating agent and reinforcing filler in poly(lactic acid) composites

This article was published in the journal, Polymer Engineering and Science [© Society of Plastics Engineers] and the definitive version is available at: http://dx.doi.org/10.1002/pen.23543The effect of talc on the crystallinity and mechanical properties of a series of poly(lactic acid) (PLA)/talc composites has been investigated. The composites were prepared by melt blending followed by compression molding. It was found that talc acted as a nucleating agent and increased the crystallinity of the PLA from 2% to 25%. There was significant improvement in Young's modulus of the composites with increasing talc addition and these results were found to fit the Halpin Tsai model. Thermo-mechanical tests confirmed that the combination of increased crystallinity and storage modulus leads to improvement in the heat distortion properties
Fabrication and characterization of poly(methyl methacrylate)/CaCu3Ti4O12 composites

Composites comprising Poly(Methyl Methacrylate) (PMMA) and CaCu3Ti4O12 (CCTO) via melt mixing followed by hot pressing were fabricated. These were characterized using X-ray diffraction, thermo gravimetric, scanning electron microscopy, and Impedance analyzer for their structural, morphology, and dielectric properties. Composites were found to have better thermal stability than that of pure PMMA. The composite, with 38 Vol % of CCTO (in PMMA), exhibited remarkably low dielectric loss at high frequencies and the low frequency relaxation is attributed to the space charge polarization/MWS effect. Theoretical models were employed to rationalize the dielectric behavior of these composites. At higher temperatures, the relaxation peak shifts to higher frequencies, due to the merging of both beta and alpha relaxations into a single dielectric dispersion peak. The AC conductivity in the high frequency region was attributed to the electronic polarization. POLYM. ENG. SCI., 54:551-558, 2014. (c) 2013 Society of Plastics Engineer
Effect of hybrid reinforcement based on precipitated silica and montmorillonite nanofillers on the mechanical properties of a silicone rubber

This is the peer reviewed version of the following article: NIK ISMAIL, N.I., ANSARIFAR, A. and SONG, M., 2014. Effect of hybrid reinforcement based on precipitated silica and montmorillonite nanofillers on the mechanical properties of a silicone rubber. Polymer Engineering and Science, 54(8), pp. 1909-1921., which has been published in final form at http://dx.doi.org/10.1002/pen.23734. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."Silicone rubber (SR) nanocomposites containing precipitated silica (PS), montmorillonite (MMT) and PS/MMT hybrid fillers were prepared through melt-mixing technique. In the SR/PS/MMT nanocomposite, the hybrid filler weight ratio was increased progressively from 0.4 to 1.7 while keeping the MMT weight constant. The viscosity, cure characteristics and mechanical properties of the nanocomposites were subsequently measured. The optimum cure time increased and the scorch time and rate of cure decreased. Furthermore, when the hybrid filler weight ratio was raised to its optimum, the tensile strength, Young’s modulus, modulus at 100% and 300% elongation (M100 and M300), elongation at break, stored energy density at break and hardness of the nanocomposite improved. The stress-strain properties of the nanocomposite with the hybrid filler improved at high deformation in comparison with those containing the PS and MMT fillers. The MMT filler exfoliated in the SR/MMT nanocomposite but did not in the nanocomposites containing the hybrid filler. Notably, the mechanical properties of the nanocomposite benefitted from the hybrid filler. This was due to the filler-filler and filler-rubber network formation in the rubber by the PS particles. Finally, effect of the PS, MMT and hybrid fillers on the energy loss or hysteresis of the rubber was measured
Preparation of micro/nanocellular polypropylene foam with crystal nucleating agents

Open-cell, porous microcellular foams with nanofibrillated structures were prepared from high tacticity isotactic polypropylene (i-PP) with a crystal nucleating and gelling agent. The 1, 3:2, 4 bis-O-(4-methylbenzylidene)-d-sorbitol gelling agent (Gel-all MD) was used as the crystal nucleating and gelling agent, which enhanced the crystallization and gelation of i-PP with a three-dimensional network of highly connected nanofibrils. The core-back foam injection molding technique was employed to foam the i-PP with nitrogen (N2) at a high expansion ratio, where the crystal nucleating agent induced bubble nucleation and bubble growth in the inter-lamella region and opened the cell walls with a nanoscale-fibrillated structure. The effects of the nucleating agent on the open cell content (OCC), density and crystallinity were thoroughly investigated. We prepared open-cell micro/nanocellular foams with an average cell size of microscale voids of < 5 μm. Nanometer-scale fibrillated structures were formed on the cell wall of the microscale void, the expansion ratio was five-fold and the open cell content was over 90%
Open-cell foams of polyethylene terephthalate/bisphenol a polycarbonate blend

Open microcellular foams of polyethylene terephthalate (PET)/polycarbonate (PC) blends were prepared by controlling their foaming behavior at the interface between these two polymers. Interface modification was a crucial factor in governing the foaming behavior and cell morphology of the blend foams: annealing at 280°C, i.e., conducting the transesterification reaction, generates a PET-b-PC copolymer, which lowers the interfacial tension, increases the affinity between PET and PC, and decreases the crystallinity of the PET domains. When CO2 foaming was performed at the interface modified with the copolymer, an interesting fibril-like structure was formed. The cell density of the PET/PC blend then increased, and its cell size reduced to the microscale while maintaining a high open-cell ratio. The effect of heat annealing (transesterification reaction) on CO2-foaming was studied to reveal the relationship among the interface affinity, crystallinity, and degree of fibrillation. The optimal heat-annealing procedure generated a fibril-like structure in the PET/PC blend foams with a high cell density (7 × 1011 cm−3), small cell size (less than 2 μm), and 100% open-cell ratio
Continuous Modification of Polypropylene Via Photoinitiation

This is the peer reviewed version of the following article: Amintowlieh, Y., Tzoganakis, C., & Penlidis, A. (n.d.). Continuous modification of polypropylene via photoinitiation. Polymer Engineering & Science, 55(10), 2423–2432 which has been published in final form at https://doi.org/10.1002/pen.24133 This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.A twin screw extruder was used for continuous modification of polypropylene (PP) via UV radiation. Long chain branches were incorporated in the PP backbone to modify its rheological properties. Benzophenone (BPH) as photoinitiator and trimethylolpropane triacrylate (TMPTA) as coagent were utilized during PP photomodification. Radiation was carried out after mixing in the extruder on solid stretched strands with approximately 0.3 mm thickness. The effects of photoinitiator concentration, radiation time and coagent presence were studied via a replicated two-level full factorial design of experiments. It was shown that photomodification of PP can be done continuously. Formation of long chain branches (LCBs) in the experimental runs was confirmed via rheological measurements. Gel content of the samples was also measured. It was found that long chain branches can be formed in PP with and without TMPTA at certain processing conditions. The amount of gel in the samples prepared with TMPTA was higher; however, the gel content could be controlled by manipulating BPH concentration and radiation time.Natural Sciences and Engineering Research Council (NSERC) of Canada
Canada Research Chair (CRC) progra