Ana B. Morales-Cepeda

Preparation and characterization of candelilla fiber (Euphorbia antisyphilitica) and its reinforcing effect in polypropylene composites

Candelilla bagasse fiber (CBF) was prepared by a mesh sieve and ball-milling process and its reinforcing effect in a polymer matrix analyzed. Composites of polypropylene (PP) and CBF were prepared by melt blending with varying amounts (20, 25, and 30xa0wt%) of fiber using maleic anhydride PP as coupling agent. The chemical composition of CBF was analyzed according to Technological Association of the Pulp and Paper Industry (TAPPI) methods, and the morphology and thermal and chemical properties of CBF and its composites were analyzed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and tensile testing. In general, fibers extracted from candelilla by a reduction process are comparable in terms of micro- and nanostructure to other lignocellulosic fibers. Dynamic light scattering (DLS) results reveal that sieve-milling reduces the fiber size. The results also show that the thermal stability of PP was enhanced when using CBF, but the crystallinity index of the PP composites decreased slightly according to DSC and XRD results. Furthermore, the Young’s modulus was increased in PP/CBF samples with and without MAPP to obtain improved wettability and fiber–polymer adhesion. We found that CBF is an excellent alternative to replace conventional materials or synthetic fibers, as well as for reinforcement in polymer composites.

EFFECT OF INITIATOR AND CROSS-LINKING AGENT ON A SEMI-IPN OF (PU-STARCH)/PMMA

The variations of the cross-linking agent, initiator, and molar ratio in the synthesis of a semi-interpenetrating polymer network (IPN) of polyurethane-starch/polymethyl methacrylate (PMMA) were studied for their viscoelastic and morphologic properties. The synthesized semi-IPNs were evaluated by means of dynamic mechanical analysis (DMA), finding that a relationship exists between the quantity of cross-linker and the storage module, where alpha and beta relaxations are present in the polymethyl methacrylates rigid chains, and this peak widens upon increasing the quantity of PMMA in the semi-IPN. The morphology of the semi-IPNs shown by SEM and AFM micrographies suggests that 0.5 wt.% of initiator and 3 wt.% of cross-linker demonstrate uniform surfaces.

Crystallization behavior of polypropylene/silver nanocomposites using polyethylene glycol as reducing agent and interface modifier

In this work, isotactic polypropylene (iPP) nanocomposites were prepared containing silver nanoparticles (Ag-NPs) with a novel and easy method, using polyethylene glycol (PEG) as reducing agent and surface modifier. Ag-NPs were prepared using different amounts in weight of silver nitrate into PEG to induce the formation of Ag-NPs. PP/Ag nano compounds were prepared by melt blend method: single-screw extruder and internal Brabender mixer. The effects of Ag-NPs and PEG on the crystallization, morphology, thermal, and mechanical properties were evaluated. Ag-NPs with a particle size of 80 nm and typical growth of the β-form in iPP were observed. The presence of PEG in samples of PP/Ag-NPs was detected by infrared spectrometry and the peak characteristic of Ag-NPs by ultraviolet–visible analysis. X-Ray diffraction patterns and differential scanning calorimetry thermograms showed the β-phase formation in both of the dispersion methods, but Brabender mixer showed higher percentages of crystallinity (31% of β-phase). The elongation at break was increased and it was directly dependent on the relative amount of crystalline β-phase. PEG is an excellent precursor to get Ag-NPs and a good interface modifier of iPP.

Carbon Fiber Composites of Pure Polypropylene and Maleated Polypropylene Blends Obtained from Injection and Compression Moulding

A comparative study of the mechanical performance of PP and PP/PP-g-MAH blends reinforced with carbon fibre (CF) obtained by two different moulding techniques is presented. Three filler contents were used for fabricating the composites: 1, 3, and 5u2009pph (parts per hundred). The crystallisation behaviour of the composites was studied by differential scanning calorimetry. Morphological and structural features of these samples were observed by atomic field microscopy and Fourier-transform infrared spectroscopy, respectively. Mechanical properties of the injection and compression moulded composites were evaluated by means of tensile and impact resistance tests. The fracture surface of the impacted samples was observed by scanning electron microscopy. The processing method had a noticeable effect on the results obtained in these tests. Young’s modulus was enhanced up to 147% when adding 5u2009pph CF to a PP matrix when processed by compression moulding. Addition of PP-g-MAH and CF had a favourable effect on the tensile and impact strength properties in most samples; these composites showed improved performance as the filler content was increased.

Deposition of Ibuprofen Crystals on Hydroxypropyl Cellulose/Polyacrylamide Gel: Experimental and Mathematic Modeling Releasing

The crystallization of nonsteroidal anti-inflammatory drug [2-(4-isobutyl-phenyl) propionic acid] ibuprofen (IBP) on a hydroxypropyl cellulose (HPC) and polyacrylamide (PAAm) gel was studied as well as the release kinetics of the drug. The IBP was crystallized on the gel surface of HPC/PAAm. It had a prismatic shape and the growth was made in an aqueous medium; the crystallinity grade of the gels HPC/PAAm and HPC/PAAm-IBU increased to 68% and to 58%, respectively. The release of IBP is performed by two means: by a non-Fickian diffusion process and by relaxation of the chains of the gel; without regard to temperature and the diffusion media, this correlates with the lower critical solution temperature (LCST) of the proposed gel. This polymer matrix provides an option for releasing nonsteroidal anti-inflammatory drugs in a temperature range of 35–39°C. Korsmeyer and Peppas mathematical model was simulated for data releases, statistically significant at 95% confidence level.

Gels from acrylic acid and hydroxypropyl cellulose via free radical polymerization

Abstract A hydrogel from acrylic acid and hydroxypropyl cellulose was made. The percentages of raw materials and crosslinkers were varied and its swelling behavior was evaluated. Some of the gels obtained absorbed more than 300% wt. The gels with higher swelling percentages were characterized by means of IR spectroscopy, differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), and scanning electron microscopy (SEM). The FTIR showed the presence of the main reactants in the gel, while the DSC showed a phase separation in the gel. This gel is partly biodegradable because of the content of hydroxypropyl cellulose and has the viscoelastic properties of poly(acrylic acid).

Influence of modified polyethylene compatibilizer on filler dispersion and flammability characteristics of linear low density polyethylene/cyclo olefin copolymer blends containing flame retardant combinations

Abstract In this study, the combination of organomodified montmorillonite (MMT), magnesium hydroxide (MDH), graphene oxide (GO) and expandable graphite (EG) as intumescent flame retardant for Linear Low-Density Polyethylene-Cyclo-Olefin Copolymer (LLDPE/COC) blends has been investigated. An amine-alcohol modified polyethylene (PEgDMAE) was used as compatibilizer. Limiting oxygen index (LOI), cone calorimeter determinations and flammability test (Underwriters Laboratory – UL-94) were used to evaluate the flame retardant properties. The structural characterization was measured by FTIR and scanning electron microscopy (SEM). The mechanical properties were also evaluated by Dynamic-mechanical analysis (DMA). The PEgDMAE compatibilizer enhanced the filler dispersion and increased the LOI to 22% for clay, 23% for GO and 26.5% for EG composites. The results indicated that the combination of each additive makes it possible to reduce the total Magnesium hydroxide filler content from 55 to 20% to achieve the flame retardant requirements. The flame retardant and mechanical properties of LLDPE/COC blends increased to a higher extent when using the combination of these additive fillers.

Composites of polypropylene/Candelilla fiber (Euphorbia antisyphilitica): Synergic of wax-polypropylene grafted Maleic anhydride

Abstract Previous studies of Candelilla bagasse fiber (CBF) have demonstrated the improvement of fiber-polymer adhesion; in the present investigation, the CBF was used to reinforce fiber of Polypropylene composites varying the amount of fiber (0, 20 and 30 wt%), using Maleic anhydride as compatibilizer. The total wax of cuticle/intercuticular varies between 9.5 and 10.5 wt%; according to the TAPPI standard Polypropylene/candellia fiber, composites were realized with intercuticular wax. The amount of fiber of 20% and 30% varied in the composite, with and without compatibilizer. In this paper, we will demonstrate that this cuticular fiber wax acts in synergy with the composite in mechanical properties, mechanical dynamics analysis to observe adherence and in “cole-cole” diagrams.

Synergistic effect of silver nanoparticle content on the optical and thermo-mechanical properties of poly(l-lactic acid)/glycerol triacetate blends

Monodispersed silver nanoparticles (Ag-NPs) were synthesized by chemical reduction in aqueous medium and transferred in chloroform to be redispersed in the plasticized matrix of poly(l-lactic acid) (PLA) by melt compounding. PLA nanocomposites were prepared using a combination of Ag-NPs in amounts of 0.01, 0.025, 0.05, 0.075 and 0.1% in weight, with 10 pph (parts per hundred) of glycerol triacetate (GTA) to be characterized by UV–Vis and Fourier transformed infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). Optical properties showed that PLA nanocomposites have monodispersed Ag-NPs due to the intense SPR (surface plasmon resonance) absorption band at 414xa0nm, with a calculated particle size ofxa0~30xa0nm. The crystallinity is gradually raised at a maximum level (21.1%) compared to the pure PLA (2.3%) and Tg drastically decreased from 61 to 36.8xa0°C when Ag-NPs are incorporated in the plasticized PLA matrix. These results were consistent with the enhanced elastic modulus in DMA analysis, explained from the viewpoint of a good nanofiller dispersion and crystallization behavior, providing a stable and ordered crystal (α-form) in agreement with FTIR and DSC analysis. Finally, the outcomes indicate a synergistic effect between Ag-NPs and the plasticizer GTA, due to the nucleating effect of the monodispersed Ag-NPs and the mobility chain promoted by the plasticizer in the macromolecular arrangement of the PLA.