Thermodynamic Parameters of Crosslinked Elastomers (BR, SBR and NBR) and Their Blends.

Herein, a methodology is employed based on the Flory-Rehner equation for estimating the Flory-Huggins interaction parameter (χ12*) of crosslinked elastomer blends. For this purpose, binary elastomer blends containing polybutadiene rubber (BR), styrene-butadiene rubber (SBR) and nitrile-butadiene rubber (NBR), were prepared in a mixing chamber at a temperature below the activation of the crosslinking agent. Swelling tests with benzene were employed to determine the crosslinked fraction, finding that after 20 min of thermal annealing, the BR and NBR were almost completely crosslinked, while the SBR only reached 60%. Additionally, the BR-SBR blend increased by 2-3 times its volume than its pure components; this could be explained based on the crosslink density. From the mechanical tests, a negative deviation from the rule of mixtures was observed, which suggested that the crosslinking was preferably carried out in the phases and not at the interface. Furthermore, tensile tests and swelling fraction (ϕsw) results were employed to determine the average molecular weight between two crosslinking points (Mc), and subsequently χ12*. Calculated χ12* values were slightly higher than those reported in the literature. The calculated thermodynamic parameters for the blends showed positive ΔGmix values and endothermic behavior, suggesting their immiscible nature.

Dibutyl Itaconate and Lauryl Methacrylate Copolymers by Emulsion Polymerization for Development of Sustainable Pressure-Sensitive Adhesives.

Renewable polymers possess the potential to replace monomers from petrochemical sources. The design and development of polymeric materials from sustainable materials are a technological challenge. The main objectives of this study were to study the microstructure of copolymers based on itaconic acid (IA), di-n-butyl itaconate (DBI), and lauryl methacrylate (LMA); and to explore and to evaluate these copolymers as pressure-sensitive adhesives (PSA). The copolymer synthesis was carried out through batch emulsion radical polymerization, an environmentally friendly process. IA was used in a small fixed amount as a functional comonomer, and LMA was selected due to low glass transition temperature (Tg). The structure of synthesized copolymers was studied by FTIR, 1H-NMR, Soxhlet extraction, and molecular weight analyses by GPC. Furthermore, the viscoelastic and thermal properties of copolymer films were characterized by DMA, DSC, and TGA. The single Tg displayed by the poly(DBI-LMA-IA) terpolymers indicates that statistical random composition copolymers were obtained. Moreover, FTIR and NMR spectra confirm the chemical structure and composition. It was found that a cross-linked microstructure and higher molecular weight are observed with an increase of LMA in the feed led. The Tg and modulus (G') of the copolymers film can be tuned with the ratio of DBI:LMA providing a platform for a wide range of applications as a biobased alternative to produce waterborne PSA.

Chemical Characterization and Enzymatic Control of Stickies in Kraft Paper Production.

Paper recycling has increased in recent years. A principal consequence of this process is the problem of addressing some polymeric components known as stickies. A deep characterization of stickies sampled over one year in a recycled paper industry in México was performed. Based on their chemical structure, an enzymatic assay was performed using lipases. Compounds found in stickies by Fourier-transform infrared spectrometry were poly (butyl-acrylate), dioctyl phthalate, poly (vinyl-acetate), and poly (vinyl-acrylate). Pulp with 4% (w/w) consistency and pH = 6.2 was sampled directly from the mill once macrostickies were removed. Stickies were quantified by counting the tacky macrostructures in the liquid fraction of the pulp using a Neubauer chamber before the paper was made, and they were analyzed with rhodamine dye and a UV lamp. Of the two commercial enzymes evaluated, the best treatment condition used Lipase 30 G (Specialty Enzymes & Biotechnologies Co®, Chino, CA, USA) at a concentration of 0.44 g/L, which decreased 35.59% of stickies. SebOil DG (Specialty Enzymes & Biotechnologies®) showed a stickies reduction of 21.5% when used at a concentration of 0.33 g/L. Stickies in kraft paper processes were actively controlled by the action of lipases, and future research should focus on how this enzyme recognizes its substrate and should apply synthetic biology to improve lipase specificity.

Poly-Lactide/Exfoliated C30B Interactions and Influence on Thermo-Mechanical Properties Due to Artificial Weathering.

Thermal stability as well as enhanced mechanical properties of poly-lactide (PLA) can increase PLA applications for short-use products. The conjunction of adequate molecular weight (MW) as well as satisfactory thermo-mechanical properties, together, can lead to the achievement of suitable properties. However, PLA is susceptible to thermal degradation and thus an undesired decay of MW and a decrease of its mechanical properties during processing. To avoid this PLA degradation, nanofiller is incorporated as reinforcement to increase its thermo-mechanical properties. There are many papers focusing on filler effects on the thermal stability and mechanical properties of PLA/nanocomposites; however, these investigations lack an explanation of polymer/filler interactions. We propose interactions between PLA and Cloisite30B (C30B) as nanofiller. We also study the effects on the thermal and mechanical properties due to molecular weight decay after exposure to artificial weathering. PLA blank and nanocomposites were subjected to three time treatments (0, 176, and 360 h) of exposure to artificial weathering in order to achieve comparable materials with different MW. MW was acquired by means of Gel Permeation Chromatography (GPC). Thermo-mechanical properties were investigated through Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), Dynamic Mechanical Thermal Analysis (DMTA) and Fourier Transform Infrared Spectroscopy (FTIR).

Morphology and thermal properties of clay/PMMA nanocomposites obtained by miniemulsion polymerization.

Miniemulsion polymerization was used as the synthetic method to produce clay/poly(methyl methacrylate) nanocomposites. Two kinds of interfacial interactions clay-polymer particle were observed by electron microscopy, one where the polymer particles are adhered on the surface of the larger fragments of clay, and another where nanometric fragments of clay are encapsulated by polymer particles. Variations in the glass transition temperature (T(g)) and thermomechanical properties of the matrix, as function of clay content, were observed. In particular, at the highest clay loading (1.0 wt%) depression of T(g) and thermomechanical properties were observed. The increased clay-polymer matrix interfacial area appears to be the conditioning factor that determines such behavior.

Comparative study on the mechanical and fracture properties of acrylic bone cements prepared with monomers containing amine groups.

In this work, the effect of the incorporation of comonomers containing amine groups on the mechanical and fracture properties of acrylic bone cements was studied. Cements were prepared with either diethyl amino ethyl acrylate (DEAEA), dimethyl amino ethyl methacrylate (DMAEM) or diethyl amino ethyl methacrylate (DEAEM) as comonomer in the liquid phase. It was found that strength and modulus decreased with increasing comonomer content in the bending and compressive tests. It was also observed that fracture toughness (K(IC)) and the critical strain energy release rate (G(IC)) increase with increasing comonomer concentration and are significantly higher compared to the control formulation. The mechanical and fracture properties of cements were also evaluated after soaking the specimens in Simulated Body Fluid (SBF) for 3 and 6 months. It was found that the mechanical properties of cements decreased when the samples were stored in SBF, although the impact strength increased in the first 3 months and then decreased. SEM micrographs were in agreement with the results obtained during mechanical characterization as the increase in toughness was confirmed by the appearance of ductile tearing pattern which is associated with plastic deformation.

Synthesis of carbon black/polystyrene conductive nanocomposite. Pickering emulsion effect characterized by TEM.

In this study, carbon black/polystyrene electrically conductive composites were obtained by suspension polymerization technique. The composite was characterized using transmission electron microscopy, which indicated two outstanding features concerning to the carbon black; first, that the carbon particles were adsorbed onto the surface of the polystyrene particles, similarly as in the Pickering emulsion phenomenon and second, that the primary aggregate structure of the carbon black was significantly affected by the dispersion process. On the other hand, the composite resistivity was in the order of 200 Ωcm, which was attributed to the direct contact of primary carbon black particles (percolation) and not to the tunneling effect. The obtained composite was evaluated as the electrically conductive element in SBR matrix.

Evidence of multi-walled carbon nanotube fragmentation induced by sonication during nanotube encapsulation via bulk-suspension polymerization.

The synthesis of multi-walled carbon nanotube/polystyrene composites, with nanotube concentrations of 0.04, 0.08 and 0.16 wt%, was carried out by in situ bulk-suspension polymerization with the assistance of sonication. By using this method both encapsulation and exfoliation of the nanotubes into the polymer host were achieved. Evidence of significant nanotube fragmentation was found by scanning electron microscopy; the cause of such fragmentation was attributed to the induction of strong cavitation due to the application of ultrasound during the synthesis. Infrared spectroscopy showed no evidence of the formation of covalent bonds between the nanotubes and the polystyrene during the process of synthesis. The thermal stability was not improved by the inclusion of the nanotubes, it was attributed to the low nanotube concentrations; however, composites glass transition temperature showed improvements.