Papers by LUIS RAMOS DE VALLE
Starch - Stärke
Environmental impact concern of conventional polymer foams has attracted considerable interest fo... more Environmental impact concern of conventional polymer foams has attracted considerable interest for the development of natural‐based polymer foams. Starch is a biopolymer that is gaining acceptability due to its renewability, availability, environmental biodegradation, and low cost. Extrusion is particularly desirable to produce starch‐based foams because it can produce a homogeneous mixing, high heat transfer, high pressure, reduction of the residence time, and low production costs. This review explains the transformation of starch during the foam processing and their relationship with extrusion conditions such as water content, barrel temperature, screw configuration and speed, die temperature, and die dimensions and how all these factors impact on the cell morphology, apparent density, expansion ratio, and final properties of starch‐based foams. The strategies to reduce water sensitivity are described, as well as the effect of amylose content and the addition of additives to impro...
Polymers for Advanced Technologies, 2022
Polymer International, 2010
The compatibilization effects provided by different amine‐functionalized polyethylenes (PEs) vers... more The compatibilization effects provided by different amine‐functionalized polyethylenes (PEs) versus those provided by a maleated polyethylene (PEgMA), for forming PE‐based film nanocomposites, were studied. Amine‐functionalized PEs were prepared by reaction of PEgMA with two primary amines, 2‐aminoethanol (EA) and 1,12‐aminododecane (D12), and a tertiary amine, 2‐[2‐(dimethylamino)ethoxy]ethanol (DMAE), in the melt to form the corresponding PEgEA, PEgD12 and PEgDMAE. Nanocomposites were prepared by melt mixing in a twin‐screw extruder PE and these three functionalized compatibilizers with a modified montmorillonite clay. The purpose of the current work was to determine the effect of the various amine‐functionalized PEs on the degree of exfoliation and optical properties of PE–clay nanocomposites in order to obtain nanocomposite films for greenhouse cover applications. Fourier transform infrared analysis confirmed the formation of the amine‐modified PE compatibilizers. Structural, mo...
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine
Temporary antibiotic-loaded cement spacers are widely used for treating chronic periprosthetic hi... more Temporary antibiotic-loaded cement spacers are widely used for treating chronic periprosthetic hip infections. The aim of this study is to evaluate the short-term tribological performance of ultra-high-molecular-weight polyethylene (UHMWPE) and (60Co) gamma-irradiated cross-linked UHMWPE (XLPE) self-mated systems as frictional pairs for temporary total hip spacers. A three-axial hip joint simulator, FIME II, was used to test the UHMWPE and XLPE self-mated systems under variable load profiles. A fetal bovine serum solution was used as a lubricant. After simulation tests, wear measurements of damaged coupled surfaces were made with a coordinate measuring machine. Finally, surfaces were characterized with scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and nanoindentation tests. The mass loss test results for UHMWPE were 11.91 ± 3.43 mg for the cups and 4.57 ± 0.92 mg for the heads. Whereas, the results for XLPE showed a significant reduction,...
Computational Materials Science, 2022
Polymer Composites, 2013
The modification of magnesium hydroxide (MH) with triethoxy vinyl silane (TVS) was carried out vi... more The modification of magnesium hydroxide (MH) with triethoxy vinyl silane (TVS) was carried out via three different methods and the results are discussed with respect to their effect on the flame retardant and the tensile properties of high density polyethylene (HDPE) nanocomposites. Via a xylene suspension of MH and TVS, via a water suspension of MH and TVS, and via powder mixing of MH and TVS. It was found that in all three cases, SiAOAMg bonds formed on the MH particles surface. Also, this silane modification induced a certain level of particle agglomeration, but without modifying their morphology or particle size. It was also found that the flame retardant properties of the HDPE nanocomposites did not improve because of the use of silane modified MH. During the flame retardant tests, all nanocomposites passed the UL-94-HB, but it was observed that the flame permanence time was longer when using modified MH. The tensile properties were negatively affected by the addition of unmodified MH; the nanocomposites became hard and brittle, with reduced flexibility. This negative effect was diminished when using silane modified MH.
Physics and Chemistry of Liquids, 2001
Densities of the binary systems 2,2′-oxybis[propane] with benzene, toluene, cyclohexane, and meth... more Densities of the binary systems 2,2′-oxybis[propane] with benzene, toluene, cyclohexane, and methyl ethanoate have been measured as a function of the composition, at 298.15 K and atmospheric pressure, using an Anton Paar DMA 5000 oscillating U-tube den-sitometer. The calculated excess volumes were correlated with the Redlich-Kister equation and with Legendre's polynomials. The excess volumes are negative for the systems of
Macromolecular Materials and Engineering, 2007
Cover: The picture depicts the mechanism of peroxide‐assisted coupling of isotatic poly(propylene... more Cover: The picture depicts the mechanism of peroxide‐assisted coupling of isotatic poly(propylene) (iPP) and carbon nanofibers (CNFs), which, in turn, leads to improved adhesion between the filler (CNF) and the polymeric matrix (iPP) and increased stiffness of the matrix. Further details can be found in the article by A. de la Vega Oyervides, J. Bonilla Ríos,* L. F. Ramos de Valle, L. A. S. de Almeida Prado, and K. Schulte on page 1095.
Journal of Applied Polymer Science, 2008
A layer of a polyethylene–silver nanoparticles composite was deposited on a five layer barrier fi... more A layer of a polyethylene–silver nanoparticles composite was deposited on a five layer barrier film structure. Different methods were used for the nanocomposite layer deposition: laminating, casting, and spraying over the multilayer structure. For the casting and spraying methods, the silver nanoparticles were previously dispersed in the polymer solution, with the assistance of ultrasound energy. The effect of silver nanoparticles and deposition method on the barrier, mechanical, and optical properties of the multilayer films was evaluated. The efficiency of silver ion release from the PE‐Silver nanocomposite deposited on the multilayer films and their antimicrobial characteristics were investigated and discussed. The silver ion release and biocide effect of the multilayer films was found to be dependant on the silver nanoparticle content and on the deposition method used. The observed results could be helpful in the design of industrial films for packaging. © 2008 Wiley Periodicals...
Journal of Vinyl and Additive Technology
Journal of Vinyl and Additive Technology
Key Engineering Materials
Addition of different contents of ground tire rubber (GTR) of different particles size in crossli... more Addition of different contents of ground tire rubber (GTR) of different particles size in crosslinked-foamed compounds based on low density polyethylene (LDPE)/ethylene vinyl acetate (EVA) was studied. Compounds were made by melt mixing in an internal mixer at 100°C and 60 rpm. Trigonox 145-45B as crosslinking agent, azodicarbonamide (ADC) as chemical blowing agent (CBA) and ZnO/SiO2as foaming co-agents, were used. GTR of 149, 74, and 44 μm particle size was incorporated as “cell nucleating agent”, each particle size at 5, 10, and 20 phr. Morphological parameters such as average cell size (d), cell size distribution and cellular density (NC) were evaluated from images acquired by scanning electron microscopy (SEM). The results obtained from the SEM characterization show a significant reduction ofd, a significance increment onNC, up to 5.81*105to 3.62*107cells/cm3and a better homogenization of the cell size distribution in the foamed compounds with high GTR contents of the smaller pa...
Journal of Applied Polymer Science
Polymer Engineering & Science
International Journal of Polymer Science, 2016
In a first step, 1,3-butadiene was selectively polymerized at 60°C in styrene as solvent using Nd... more In a first step, 1,3-butadiene was selectively polymerized at 60°C in styrene as solvent using NdV3/DIBAH/EASC as the catalyst system. The catalyst system activation process, the addition order of monomers and catalyst components, and the molar ratios [Al]/[Nd] and [Cl]/[Nd] were studied. The catalyst system allowed the selective 1,3-butadiene polymerization, reaching conversions between 57.5 and 88.1% with low polystyrene contents in the order of 6.3 to 15.4%. Molecular weights ranging from 39,000 to 150,000 g/mol were obtained, while cis-1,4 content was found in the interval of 94.4 to 96.4%. On the other hand, the glass transition temperatures of synthesized materials were established in the range of −101.9 to −107.4°C, explained by the presence of polystyrene segments in the polybutadiene chains; in the same sense, the polybutadienes did not show the typical melting endotherm of high cis-polybutadienes. In a second step, the resulting styrene/high cis-1,4 polybutadiene solutions...
Journal of Nanomaterials, 2016
Morphological evolution and dielectric properties of poly(ethylene naphthalate)- (PEN-) graphene ... more Morphological evolution and dielectric properties of poly(ethylene naphthalate)- (PEN-) graphene nanocomposites nonisothermally crystallized have been investigated. PEN-graphene nanocomposites containing 0.01, 0.025, 0.05, 0.075, and 0.1 wt% of graphene were prepared by melt blending in a mini twin screw extruder. The results showed that graphene exhibited a superior influence on morphological and conformational structure of PEN during nonisothermal crystallization at low graphene contents. Crystallization temperature (Tc) was found to be increased up to 18°C supporting the high nucleating activity of graphene layers. Wide angle X-ray diffraction (WAXD) and Fourier Transform Infrared Spectroscopy (FTIR) indicated that graphene modifies the conformation of PEN chains promoting crystallinity and favoring the evolution from α to β crystalline form with homogeneous lamellar thickness. It may be attributed to the structural similarity between naphthalene rings and graphene structure and ...
International Journal of Material Forming, 2015
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Papers by LUIS RAMOS DE VALLE