Suspensions of cellulose microfibrils resulting from the homogenization of parenchymal cell walls were surface silylated with isopropyl dimethylchlorosilane. When mild silylation conditions were ...applied, the microfibrils retained their morphology, but could be dispersed in a non-flocculating manner into organic solvents. The rheological properties of these suspensions in methyl oleate were investigated, using a range of concentrations and shear rates. The suspensions presented characteristic thickening and shear thinning effect, but no marked yield stress point. These properties are discussed and compared with those of the aqueous suspension of the parent un-derivatized microfibrils.
The influence of nanoclays on the structural changes of hydrated poly(l-lactic acid) (PLLA) was investigated at two temperatures, above and below its Tg. Samples of a commercial PLLA and ...nanocomposites with 2 wt% of an organically modified montmorillonite and an unmodified halloysite were kept in a phosphate buffered solution for different times at 37 and 58 °C and then characterized. The crystallinity degrees and the nature of the crystalline structures developed were determined by differential scanning calorimetry, X-Ray Diffraction and Fourier Transform infrared spectroscopy. While in the cold crystallization of PLLA in dry conditions the α form is obtained only above 100 °C, different mixtures of α and α′ forms were obtained in water at 58 °C, depending on the clay used. The hydrolytic degradation of PLLA played a main role in the structural transformations found at long immersion times, since the short chains formed allowed greater crystallinity degrees and leaded to more perfect crystals. PLLA structure is changed by clays because of its ability as nucleating agents but also due to its effect on the hydrolytic degradation. The unmodified tubular halloysite inhibited degradation, so that lower degrees of crystallinity were obtained in the halloysite based nanocomposite. On the other hand, the modified montmorillonite acted as catalyst of degradation, which explained the appearance of crystalline structures in the nanocomposite with montmorillonite after 84 days of immersion at 37 °C.
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•Mixtures of α and α′ polymorphs are developed in hydrated PLLA at 58 °C.•Hydrolysis plays a main role in the PLLA crystallization at long immersion times.•The crystallization of hydrated PLLA depends on the chemical nature of the clay.•Montmorillonite induces the crystallization of hydrated PLLA even at 37 °C.
Mixed matrix membranes, MMM, based on polyethylene, PE, and silica mesoporous material, MCM-41, have been prepared using these hybrid materials obtained by in situ polymerization in order to achieve ...higher permeability, selectivity or both magnitudes relative to the existing polymeric PE membranes. Different methodologies are used to enhance interfacial adhesion between components, PE matrix and MCM-41. These basically consist of promoting the modification of MCM-41 surface with undecenoic acid, UA/triisobutylaluminum, TIBA, system before the polymerization and of incorporating UA in the polymer chains by copolymerization. The influence of UA on the degradation behavior is evaluated for all of the hybrids and the transport properties, in terms of permeability and diffusivity coefficients as well as permselectivity at different gases and temperatures are checked in some of the resulting materials.
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► Several approaches are checked for decorating MCM-41/PE hybrids. ► Effective interactions between UA/TIBA with the silanol surface groups of the MCM-41 are detected. ► Incorporation of MCM-41 increases permeability of O2, N2 and CO2 compared with those for HDPE. ► Membranes are prepared by melt compression, an attractive protocol from industrial standpoint.
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► Novel hybrids based on PVDF and different contents of Cu nanoparticles have been prepared. ► A complete structural and morphological characterization of the nanocomposites has been ...performed. ► Interactions between PVDF matrix and Cu nanoparticles is deduced from FTIR. ► Attenuation of the electromagnetic radiation increases spectacularly with the Cu content.
Novel hybrids based on PVDF and varied concentration of Cu nanoparticles have been prepared in order to analyze their electromagnetic interference shielding response and, consequently, their capability to be a good alternative to replace metals for that application. Very promising results have been found in this area. Moreover, a complete structural and morphological characterization, as well as a previous evaluation of their mechanical behavior, has also been performed.
This work covers the synthesis and characterization of in-reactor Ultra-High Molecular Weight Polyethylene/High Density Polyethylene, UHMWPE/HDPE, blends by in situ polymerization in a single ...reactor, through dual catalyst immobilization. These blends are synthesized combining two different catalysts (one for each targeted molar mass) co-immobilized in mesoporous Santa Barbara Amorphous, SBA-15, particles. First, the ethylene polymerization behavior is investigated, under different polymerization conditions. Then, studies on the thermal, mechanical and rheological characteristics of the produced in-reactor blends are presented and their performance is compared and discussed in a comprehensive way. Moreover, the effect of different filler contents on the properties exhibited by the resulting materials is investigated. Results have shown that these in-reactor UHMWPE/HDPE blends exhibit a complex thermal, mechanical and rheological behavior, which depends mainly on the proportion between the two polymer components and on the amount of SBA-15.
Incorporation of a small content of undecenoic acid is proposed as an approach to introduce polar groups within the macromolecular architecture of high density polyethylene-based materials in order ...to promote an easier degradation after their useful service life. The influence of these hydrophilic groups during thermo and photo-oxidation processes has been then evaluated by several complementary techniques. In addition to different degradation rates, distinct ratios of oxidized species (lactones, ketones, carboxylic acids, esters and aldehydes) are found depending on: a) the initial material (neat high density polyethylene or ethylene-co-undecenoic acid copolymer); b) the type of oxidation (thermo or photoinduced); and c) the absence or presence of a specific prodegradant additive. An important increase of crystallinity has been observed in the final oxidized samples, indicating that the extent of degradation is rather significant.
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•PVDF–TiO2 nanocomposites are highly efficient biocidal materials under UV light.•These hybrids surprisingly maintain antimicrobial features within visible range.•Appropriate ...interfacial interactions lead to an increase of the absorption at visible region.•Anatase incorporation does not alter the PVDF crystalline lattice developed.•Some crystalline characteristics are dependent on TiO2 content.
Highly efficient antibacterial nanocomposite films consisting of a commercially available poly(vinylidene difluoride) (PVDF) incorporating synthesized TiO2 nanoparticles have been prepared with different anatase contents by a simple approach with absence of any solvent. These materials display powerful antimicrobial activity toward both Gram-negative and Gram-positive bacteria under UV and, surprisingly, visible lights. Their optical characterization has pointed out that absorption is significantly increased in the nanocomposites at the visible range, being this aspect behind the excellent capability exhibited against microorganisms.
Prodegradant additives (PDA) came up in the last few decades as a possible solution to the low degradability of polyolefins. PDAs attack polyolefins chains cutting and degrading them to a degree that ...eventually may allow phagocytosis by microorganisms. Also, considering that the PDA is added in very low quantities, main additives suppliers affirm that a priori they neither alter mechanical properties nor the recyclability of the polymer. In order to verify these claims, this work comprehends a systematic study to analyze the effectiveness of some commercially available PDAs on different polyolefins. Diverse degradability analysis of LDPE, HDPE and PP additivated with 1 and 2 wt% of PDA were performed comparing changes on molecular weights, rheological and mechanical properties among them and base polyolefins, all under two kinds of experiments: natural and UV accelerated aging. It was found that the addition of PDA accelerates degradation since after both aging processes samples with PDA were significantly more degraded than base polyolefins under same conditions. Moreover, processing also contributes to the degradation process, being more noticeable in PP. However, results demonstrate that chain scission of polyolefins additivated with PDA is not being improved to an extent that would allow biodegradation.
Ethylene–vinyl alcohol, EVOH, copolymers with two different vinyl alcohol compositions have been modified to incorporate different reactive functional groups by using phthalic anhydride, chloroacetyl ...chloride and 4-nitrophenyl chloroformate. Moreover, coupling reactions between EVOH copolymers functionalized with 4-nitrophenyl carbonate groups and three aminosaccharides (d-(+)-glucosamine, d-(+)-galactosamine and d-(+)-mannosamine) have been carried out in dimethyl sulfoxide at 70°C. The structure of the resulting functionalized copolymers and new glycopolymers was confirmed by FTIR, 1H and 13C NMR. In addition, the thermal characterization of glycopolymers has been performed by DSC. A unique thermal transition, ascribed to the glass transition, is observed in both glycopolymer series. The semicrystalline character of the initial EVOH copolymers is vanished and complete amorphous polymeric materials are obtained since the resulting glycopolymers present relatively long and bulky pendant chains impossible to be included in the EVOH crystallites.
Isotactic propene/higher α-olefin quenched copolymers at intermediate commoner contents primarily crystallize into a mesomorphic phase.
Several isotactic propene-α-olefin copolymers using 1-octene, ...1-dodecene and 1-tetradecene as comonomers (CiPO, CiPDD and CiPTD, respectively) have been synthesized and their structure and thermal/mechanical/viscoelastic properties have been evaluated. At intermediate comonomer molar content ranged from around 4 to 9, the mesomorphic phase is developed under rather mild quenching conditions and independently of length of the comonomer. Thermal and mechanical parameters diminish as α-olefin content increases and their dependence on composition changes as function of existence of three-dimensional monoclinic crystallites or less ordered entities.
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