M.U. de la Orden

Comparative spectroscopic study of the modification of cellulosic materials with different coupling agents

The reactions of two cellulosic materials (an industrial cellulosic by-product from a Kraft pulp mill facility and a reference material) with three coupling agents, used to improve compatibility between cellulosic reinforcements and thermoplastic matrices, were studied by diffuse reflectance Fourier-transform infrared (DRIFT) spectroscopy and diffuse reflectance ultraviolet-visible spectroscopy. A maleated polypropylene wax (Epolene E-43™) and two silanes (N-2-aminoethyl-3-aminopropyltrimethoxysilane and methyltrimethoxysilane) were used as coupling agents. The two cellulosic materials reacted in a similar way and the three coupling agents were covalently bonded to the cellulose. For the aminosilane, a reaction with cellulose involving a fraction of the amino groups was detected. A simple method, based on the analysis of the oxidation kinetics of treated and untreated materials, was developed to compare the degree of cellulose modification achieved by each coupling agent. The analysis revealed that a reduced fraction of the cellulose reactive groups was converted by esterification with the maleated polypropylene. However, when applied in the appropriate conditions, the two silanes converted most of such cellulose reactive groups. Finally, the reaction of cellulose with mixtures of coupling agents was studied. The aminosilane-treated cellulose reacted with the maleated polypropylene with formation of amide links.

Abrasion resistance in the Tumble test of sol–gel hybrid coatings for ophthalmic plastic lenses

Hard abrasion-resistant coatings for ophthalmic plastics were obtained from mixtures of tetraethoxysilane, 3-metacryloxypropyltrimethoxysilane and methyl methacrylate, and were cured at 120°C and 140°C for different times. The Tumble test was used to measure the abrasion resistance of these coated plastics. This abrasion resistance was strongly dependent on the curing time and temperature. The infrared analysis of the curing processes showed that, in order to achieve the highest abrasion resistance, these acrylic hybrid coatings must be fully polymerized, but overcuring must be carefully avoided. Finally, a linear correlation was found between the abrasion resistance of these coated samples (as measured by the Tumble test) and their microhardness.

Study of the effects of the reaction conditions on the modification of clays with polyelectrolytes and silanes

New organically modified clays have been obtained from sodium montmorillonite, using either a cationic polyelectrolyte (polyethylenimine) or a novel homemade bisphenol-A silane as modifiers. The modification processes have been carried out in different reaction media, in order to study the effects on the properties of the modified clays of several reaction parameters, such as the pH of the polyethylenimine solution or the nature of the solvent used in the silanization. The obtained clays were characterized using X-ray diffraction, thermogravimetric analysis, and FTIR spectroscopy. Clays modified with polyelectrolyte or silane show significant increases in the basal spacing. The properties of polyelectrolyte-modified clays depend on the pH of the treating solution. The increase in the basal spacing of polyelectrolyte-modified clays varies only slightly with the pH; however, this reaction parameter clearly determines the total amount of polyelectrolyte introduced in the clay. The properties and applications of silane-modified clays are strongly dependent on the presence of water in the reaction media used for the silanization. These results have been explained by considering that the reaction conditions determine the nature and the amount of material intercalated into the clay.

Effect of E-glass short fibre on the degradation of polypropylene

Abstract The effect of E-glass short fibre on the degradation of polypropylene was studied by thermogravimetric and differential thermal analysis. This filler catalyses degradation at low temperature, particularly in air, catalysis being strongly dependent upon the nature of the fibre surface; catalysis is prevented by pretreatment with HCl, which partly dissolves the soluble oxides of the fibre surface and intensely hydrates the fibre.

Thermal and fourier transform-infrared study of E-glass short-fiber functionalization with methylvinyldichlorosilane and vinyltrichlorosilane

Abstract Thermal analysis and Fourier transform-infrared (FT-IR) spectroscopy were used to study the nature of the coatings deposited on E-glass short fibers by treatments with methylvinyldichlorosilane (MVDCS) and vinyltrichlorosilane (VTCS) applied from various reaction media. The coatings obtained from aqueous or toluene solutions of both silanes were polysiloxanes and showed high thermal stability in a nitrogen atmosphere. However, in an air atmosphere, vinyl group oxidation occurred at temperatures near 200°C. Coatings obtained from toluene solutions in the presence of pyridine consisted mostly of pyridinium chloride, which could be removed by heating at 100°C. After heating at 100°C, a coating consisting of polyvinylsiloxanes subsisted on fibers treated with VTCS. However, no stable coatings were obtained from MVDCS under these reaction conditions.

Thermal and FTIR study of E-glass short fiber functionalization with chloromethyldimethylchlorosilane

Abstract The functionalization of E-glass short fibers by treatment with chloromethyldimethylchlorosilane has been studied in various media. Both thermal and FTIR analysis indicated that pyridine-catalyzed reaction in refluxing toluene produced surface immobilization of the -Si(CH3)2CH2-N+C 5H5 Cl− group by siloxane bonds, while refluxing in toluene alone failed to immobilize silane. This coating shows high thermal stability. In aqueous solution at pH 3.3, a deposit forms consisting of substantial amounts of silane (removed at 80°C) together with a small quantity of the -Si(CH3)2CH2Cl group coupled to the surface by siloxane bonds (removed only above 350°C).

Effects of previous leaching with hydrochloric acid of E-glass short fibre on the fibre reaction with chlorosilanes

Abstract Leaching of E-glass fibres with HCl and its effect on the reaction of fibre with chlorosilanes were studied by FTIR spectroscopy and thermal analysis. Leaching removes basic oxides from the fibre, increases fibre surface area and causes intense surface hydration as well as water diffusion into the fibre. Fibre hydration can be reduced by drying the fibre at high temperatures. Surface hydration increases the amount of polyvinylsiloxane coating formed when fibre reacts with vinyltrichlorosilane in refluxing toluene, but prevents the fibre from reacting with monochlorosilanes in toluene or aqueous solution.

Effects of Aging and Different Mechanical Recycling Processes on the Structure and Properties of Poly(lactic acid)-clay Nanocomposites

The growing use of poly(lactic acid) (PLA) and PLA-based nanocomposites in packaging has raised the interest of studying the mechanical recycling of the wastes and the properties of the recycled materials. The main objective of this work was to study the effect of two different mechanical recycling processes on the structure and properties of a PLA-montmorillonite nanocomposite. The two recycling processes included accelerated thermal and photochemical aging steps to simulate the degradation experienced by post-consumer plastics during their service life. One of them also included a demanding washing process prior to the reprocessing. A decrease in the molecular weight of PLA was observed in the recycled materials, especially in those subjected to the washing step, which explained the small decrease in microhardness and the increased water uptake at long immersion times. Water absorption at short immersion times was similar in virgin and recycled materials and was accurately described using a Fickian model. The recycled materials showed increased thermal, optical and gas barrier properties due to the improved clay dispersion that was observed by XRD and TEM analysis. The results suggest that recycled PLA-clay nanocomposites can be used in demanding applications.

FTIR Study on Chemical Modification of E-Glass Short Fiber with Tert-Butyldiphenylchlorosilane

Abstract The reaction of E-glass short fibers with tert-butyldiphenylchlorosilane (TBDPCS) and trimethylchlorosilane (TMCS) was studied by FTIR spectroscopy in water and in toluene. Fiber coating obtained from TMCS in aqueous solution contained siloxane bonds, by which the trimethylsilyl group was attached to the glass surface. Coatings obtained from TBDPCS, however, consisted of silane and silanol, and no siloxane bonds were observed. This may be attributed to the effect of steric hindrance in the reaction.