Polimerização 1,4-cis de butadieno com sistemas catalíticos Ziegler-Natta à base de neodímio

Nowadays the catalyst systems based on neodymium are the ones most used in the high cis polybutadiene production. These systems contain a neodymium compound (catalyst), an alkylaluminium compound (cocatalyst) and a halogen compound (halogenating agent). The microstructure, molecular weight characteristics and the reaction activity are influenced by the nature and concentration of catalyst system components. Those characteristics are also affected by the polymerization conditions. This paper presents a brief review on 1,4-cis-butadiene polymerization on neodymium catalysts.

Desempenho físico-químico e mecânico de concreto de cimento Portland com borracha de estireno-butadieno reciclada de pneus

Physicochemical and mechanical techniques were carried out to characterize three concrete tyre-rubber waste dosages such as 5, 10 and 15%, w/w. The elastomeric material was identified as styrene-butadiene rubber (SBR). It was observed that the growing SBR content in the mixture decreased the concrete performance. The best results were presented by 5% w/w tyre-rubber waste concrete sample. This composition was tested at Mourão hydroelectric powerplant spillway as repairing material.

Étude de dispositifs électroniques moléculaires à l'aide de modèles simples

Cette thèse en électronique moléculaire porte essentiellement sur le développement d’une méthode pour le calcul de la transmission de dispositifs électroniques moléculaires (DEMs), c’est-à-dire des molécules branchées à des contacts qui forment un dispositif électronique de taille moléculaire. D’une part, la méthode développée vise à apporter un point de vue différent de celui provenant des méthodes déjà existantes pour ce type de calculs. D’autre part, elle permet d’intégrer de manière rigoureuse des outils théoriques déjà développés dans le but d’augmenter la qualité des calculs. Les exemples simples présentés dans ce travail permettent de mettre en lumière certains phénomènes, tel que l’interférence destructive dans les dispositifs électroniques moléculaires. Les chapitres proviennent d’articles publiés dans la littérature. Au chapitre 2, nous étudions à l’aide d’un modèle fini avec la méthode de la théorie de la fonctionnelle de la densité de Kohn-Sham un point quantique moléculaire. De plus, nous calculons la conductance du point quantique moléculaire avec une implémentation de la formule de Landauer. Nous trouvons que la structure électronique et la conductance moléculaire dépendent fortement de la fonctionnelle d’échange et de corrélation employée. Au chapitre 3, nous discutons de l’effet de l’ajout d’une chaîne ramifiée à des molécules conductrices sur la probabilité de transmission de dispositifs électroniques moléculaires. Nous trouvons que des interférences destructives apparaissent aux valeurs propres de l’énergie des chaînes ramifiées isolées, si ces valeurs ne correspondent pas à des états localisés éloignés du conducteur moléculaire. Au chapitre 4, nous montrons que les dispositifs électroniques moléculaires contenant une molécule aromatique présentent généralement des courants circulaires qui sont associés aux phénomènes d’interférence destructive dans ces systèmes. Au chapitre 5, nous employons l’approche « source-sink potential » (SSP) pour étudier la transmission de dispositifs électroniques moléculaires. Au lieu de considérer les potentiels de sources et de drains exactement, nous utilisons la théorie des perturbations pour trouver une expression de la probabilité de transmission, T(E) = 1 − |r(E)|2, où r(E) est le coefficient de réflexion qui dépend de l’énergie. Cette expression dépend des propriétés de la molécule isolée, en effet nous montrons que c’est la densité orbitalaire sur les atomes de la molécule qui sont connectés aux contacts qui détermine principalement la transmission du dispositif à une énergie de l’électron incident donnée. Au chapitre 6, nous présentons une extension de l’approche SSP à un canal pour des dispositifs électroniques moléculaires à plusieurs canaux. La méthode à multiples canaux proposée repose sur une description des canaux propres des états conducteurs du dispositif électronique moléculaire (DEM) qui sont obtenus par un algorithme auto-cohérent. Finalement, nous utilisons le modèle développé afin d’étudier la transmission du 1-phényl-1,3-butadiène branché à deux rangées d’atomes couplées agissant comme contacts à gauche et à la droite.

Low Temperature Curing of NBR for Property Improvement

Zinc salts of ethyl, isopropyl, and butyl xanthates are prepared in the laboratory, and the effect of these xanthates with zinc diethyl dithiocarbamate (ZDC) on the vulcanization of HAF-filled nitrile butadiene rubber (NBR) compounds has been studied at different temperatures. The cure times of these compounds have been compared with that of NBR compounds containing TMTD/MBTS. The rubber compounds with the three xanthate accelerators and ZDC are cured at various temperatures from 60 to 150°C. The sheets are molded and properties such as tensile strength, tear strength, cross-link density, elongation at break, compression set, abrasion resistance, flex resistance, etc. have been evaluated. The properties show that zinc salt of the xanthate/ZDC accelerator system has a positive synergistic effect on the cure rate and mechanical properties of NBR compounds.

Studies on NBR/PVC Blends

Studies conducted on butadiene-acrylonitrile copolymer (NBR)/poly(vinyl chloride) (PVC) blends at different temperatures indicate that an optimum temperature exists for the formation of a particular blend. The mechanical properties of the blends confirm this observation. PVC stabilizer based on, magnesium oxide , zinc oxide, and stearic acid was found to be very useful in NBR/PVC blends.

Starved Extrusion for the Improvement of Mechanical Properties of Rubber Vulcanizates

Filled compounds of natural rubber, isobutylene-isoprene rubber and styrene-butadiene rubber compounds were extruded through a laboratory extruder by varying the feeding rate at different temperatures and revolutions per minute. The extruded compounds were vulcanized up to their optimum cure times and the mechanical properties of the vulcanizates were determined. The properties suggest that there is a particular feeding rate in the starved fed region which results in maximum mechanical properties. The study shows that running the extruder at a slightly starved condition is an attractive means of improving the physical properties.

Polymer-Solvent Interaction Parameter for NR/SBR and NR/BR Blends

Polymer-solvent interaction parameters for the blends of natural rubber (NR) with styrene-butadiene rubber (SBR) and polybutadiene rubber ( BR) are calculated using the Flory-Rehner equation by equating the network density of the vulcanizates in two solvents.

Studies on the Cure Characteristics of Elastomer Blends

Blends of natural rubber (NR) with styrene-butadiene rubber (SBR), polybutadiene rubber (BR), ethylene-propylene terpolymer (EPDM) and acrylonitrile-butadiene rubber (NBR) were vulcanised using an efficient vulcanisation (EV) system and a semi-EV system. Compatible blends show a definite pattern of curing whereas the incompatible blends show no such pattern.

Studies on the Cure Characteristics and Vulcanizate Properties of 50 / 50 NR /SBR Blend

Blends of 50/50 natural rubber (NR) and styrene-butadiene rubber (SBR) are vulcanized using several conventional and semi-EV systems. The cure characteristics and vulcanizate properties are compared. The quantity and quality of crosslinks in each case are deciphered by chemical probes to correlate them with the vulcanizate properties.

Effect of Blending Techniques on the Curing of Elastomer Blends

Compounding of styrene-butadiene copolymer/polybutadiene , natural rubber/ ethylene-propylene-diene terpolymer and natural rubber/butadiene-acrylonitrile copolymer blends was done in three different ways and their curing behaviour and the tensile properties of the es are compared.

Rubber Seed Oil: A Multipurpose Additive in NR and SBR Compounds

ABSTRACT: Rubber seed oil was used as a multipurpose ingredient in natural rubber (NR) and styrene butadiene rubber (SBR) compounds. The study shows that the oil, when substituted for conventional plasticiser, imparts excellent mechanical properties to NR and SBR vulcanizates. Further, it also improves aging resistance, reduces cure time, increases abrasion resistance and flex resistance, and reduces blooming.

Development of Elastomeric Hybrid Composite Based on Synthesised Manosilica and Short Nylon Fiber

Nanoscale silica was synthesized by precipitation method using sodium silicate and dilute hydrochloric acid under controlled conditions. The synthesized silica was characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), BET adsorption and X-Ray Diffraction (XRD). The particle size of silica was calculated to be 13 nm from the XRD results and the surface area was found to be 295 m2/g by BET method. The performance of this synthesized nanosilica as a reinforcing filler in natural rubber (NR) compound was investigated. The commercial silica was used as the reference material. Nanosilica was found to be effective reinforcing filler in natural rubber compound. Filler-matrix interaction was better for nanosilica than the commercial silica. The synthesized nanosilica was used in place of conventional silica in HRH (hexamethylene tetramine, resorcinol and silica) bonding system for natural rubber and styrene butadiene rubber / Nylon 6 short fiber composites. The efficiency of HRH bonding system based on nanosilica was better. Nanosilica was also used as reinforcing filler in rubber / Nylon 6 short fiber hybrid composite. The cure, mechanical, ageing, thermal and dynamic mechanical properties of nanosilica / Nylon 6 short fiber / elastomeric hybrid composites were studied in detail. The matrices used were natural rubber (NR), nitrile rubber (NBR), styrene butadiene rubber (SBR) and chloroprene rubber (CR). Fiber loading was varied from 0 to 30 parts per hundred rubber (phr) and silica loading was varied from 0 to 9 phr. Hexa:Resorcinol:Silica (HRH) ratio was maintained as 2:2:1. HRH loading was adjusted to 16% of the fiber loading. Minimum torque, maximum torque and cure time increased with silica loading. Cure rate increased with fiber loading and decreased with silica content. The hybrid composites showed improved mechanical properties in the presence of nanosilica. Tensile strength showed a dip at 10 phr fiber loading in the case of NR and CR while it continuously increased with fiber loading in the case of NBR and SBR. The nanosilica improved the tensile strength, modulus and tear strength better than the conventional silica. Abrasion resistance and hardness were also better for the nanosilica composites. Resilience and compression set were adversely affected. Hybrid composites showed anisotropy in mechanical properties. Retention in ageing improved with fiber loading and was better for nanosilica-filled hybrid composites. The nanosilica also improved the thermal stability of the hybrid composite better than the commercial silica. All the composites underwent two-step thermal degradation. Kinetic studies showed that the degradation of all the elastomeric composites followed a first-order reaction. Dynamic mechanical analysis revealed that storage modulus (E’) and loss modulus (E”) increased with nanosiica content, fiber loading and frequency for all the composites, independent of the matrix. The highest rate of increase was registered for NBR rubber.

Studies on the use of nano zinc oxide and modified silica in NR, CR and SBR

Department of Applied Chemistry, Cochin University of Science and Technology

Studies on short nylon fiber - reclaimed rubber/elastomer composites

The thesis deals with the development of short nylon fiber-reclaimed rubber/elastomer composites. Three rubbers viz, natural rubber, acrylonitrile butadiene rubber and styrene butadiene rubber were selected and were partially replaced with reclaimed rubber. The blend ratio was optimized with respect to cure characteristics and mechanical properties. Reclaimed rubber replaced 40 parts of NR and SBR and 20 parts of NBR without much affecting the properties. These blends were then reinforced with short nylon fibers. The mechanical properties of the composites were studied in detail. In all the cases the tensile strength, tear strength and the abrasion resistance increased with increase in fiber content. In the case of NRlreclaimed rubber blends, the tensile strength-fiberloading relationship was non-linear where as in the case of NBRlreclaimed rubber blends and SBRlreclaimed rubber blends the tensile strength-fiber loading relationship was linear. All the composites showed anisotropy in mechanical properties. The effect of bonding system on the composite properties was also studied with respect to cure characteristics and mechanical properties. For this, a 20 phr fiber loaded reclaimed rubber/elastomer composites were selected and the effect of MDI/PEG resin system was studied. The resin used was 5 phr and the resin ratios used were 0.67: I, 1:1, 1.5:1 and 2:1. The bonding system improved the tensile strength, tear strength and abrasion resistance. The best results are with SBRlreclaimed rubber-short nylon fiber composites. The optimized resin ratio was 1:1 MDI/PEG for all the composites.