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This work investigates natural rubber (NR) composites vulcanized with different combinations of accelerators in efficient cure systems. The NR compounds were characterized for cross-link density, hardness, tensile strength, and dynamical–mechanical properties, before and after aging. Among the cure systems used, that containing the highest amount of free sulfur presented the best mechanical performance, before and after aging; concerning dynamic properties after the aging, the composition with a lower number of cross-links was the best.

Carbon black and high performance silica have been widely employed as binary system filler in tire tread formulations. This study evaluated the total and partial substitution of silica by metakaolin (MK) on the properties of tread rubber composites. Dynamic mechanical thermal analysis and abrasion tests were conducted as typical assessments of tire tread performance: rolling resistance (fuel consumption), wet traction (safety), and abrasion (durability). Further the energy spent by the equipment during the processing of formulations was also analyzed, as well as rheological and mechanical properties. A significant reduction of rolling resistance was obtained with 75% and 100% of silica substitution by MK, which could lead to lower heat buildup in tire tread applications, without showing negative effects on wet traction, although abrasion showed undesired results. The substitution of silica by MK also lowered energy demanded for processing. No major changes were observed in vulcanization parameters and mechanical properties, which is interesting considering the fact that MK is nonreinforce filler.

Rubber dams employed for endodontic treatment are commonly based on natural rubber latex compounds and it is essential that they remain unbroken throughout the different procedures. The in-use failure of some types of rubber dams can be related to the time spent under tension in contact with saliva and/or to sodium hypochlorite. Five different types of commercial rubber dams were assessed with respect to physico-mechanical properties (crosslink density, stress at break, tear strength and stress relaxation), morphological aspects (Scanning Electron Microscopy), and elemental analyses (energy-dispersive X-ray spectrometry). Moreover, a special bench apparatus was developed to mimic actual conditions of rubber dams during endodontic procedures. Results showed that the device performance was reliable and comparable to observations during clinical activity corroborated by the stress relaxation test. Samples based on sulfur curing system with predominance of accelerator has better performance under stress relaxation tests than those samples with higher concentration of sulfur.

Fluoromica is a clay mineral obtained from chemical modification of talc with Na2SiF6. In this study, it was used to prepare clay mineral polymer composites (CPN) based on nitrile rubber. The composites were compounded in a roll mill and it was studied the effect of the fluoromica content as well as the shear ratio employed during the preparation. The composites were assessed based on the mechanical properties, dynamic-mechanical performances, rheological properties, and morphological aspects. The results suggested that the formation of chemical crosslinks was affected with the presence of the clay mineral, moreover, little or no reinforcement effect was achieved most likely to the lack of interaction with the matrix.

This work aims at studying not only the rheological behavior of natural rubber-based compositions by making use of different contents of fluoromica or ME 100 synthetic mica in a natural rubber (NR) matrix, but also the different filler-filler and matrix-filler interactions before and after curing. The ME 100 content in NR varied from 0 to 10 phr (parts per hundred parts of resin) and the results enabled to conclude on the influence of the mineral filler on the curing parameters, as well as on the limit amount of ME 100 for the best performance resulting from the best filler distribution/interaction in the polymer matrix. All data were compared with those of the unfilled composition. Based on complex viscosity, curing parameters, dynamic modulus and Payne effect tests it was concluded that the mica content limit for the best performance was 7 phr.

Epoxidized natural rubber (ENR) and synthetic non-modified hydrotalcite (HT) compounds were prepared and evaluated. Natural rubber (NR) was epoxidized with 20.6% of epoxy groups from a chemical modification of the latex. A sulfur-based curing system formulation with accelerators was used. The amounts of HT in the ENR-HT compositions was varied between 0, 2, 3 and 5 phr. All compositions were evaluated as to cure parameters, rheological properties, thermal resistance and crosslink density. The results showed that the mineral filler does not have a significant influence on the cure parameters. Different methods of crosslink density determination were used (swelling at equilibrium and elastic modulus). The results turn out to be equivalent and rise as the amount of filler is increased. The best results were found for the 5 phr hydrotalcite compound (ENR-HT5).

A method is proposed in order to reduce significantly the influence of the coating shear stress and its cohesion failure on the normal adhesion stress of metallic films on polymers. Most methods used so far were not able to avoid the interference of the cohesion failure when the interface was delaminated in order to measure the adhesion strength. Our method has been proved to work and the results are more accurate than the standard pull-off method. The experiments consisted in delaminating copper films deposited by physical vapor deposition on four different kinds of polymeric substrates: polypropylene, polyamide 6, high impact polystyrene and polyethylene terephthalate. The polymer surfaces have also been modified by means of substrate sanding and flaming processes. Optical and scanning electron microscopies were used to study the morphology of both the removed copper film and the polymer surface after pulling-off. Adhesion work was measured by contact angle to determine the necessary energy to pull-off the metal–polymer interface.

The focus of this paper is to establish a characterisation method for seven polyamide (PA) grades to determine the major material to manufacture an automotive worm gear. The composite properties were measured according to the worm gear loadings: tensile strength, Young’s modulus, abrasion and impact resistance. They were also correlated to the PA moisture absorption and its glass fibre (GF) reinforcement. The data from mechanical tests were applied in the finite element analysis (FEA) using the von Mises stress criterion. Before the rig tests of the PA worm gears, the injection process was evaluated, through the capillary rheometry. A higher difficulty to process PA 6/6 30% GF was found, due to its lower apparent viscosity. In the end, the influence of moisture absorption was as decisive to the gear’s material selection as the GF to the pinion. Thus, the PAs with the best performance were: PA 6 with 30% GF (gear) and with PA 60% GF (pinion).

A reciclagem de resíduos de borracha é de extrema importância nos dias de hoje, tanto em relação aos impactos ambientais quanto à conservação de energia. Considerando que a maioria dos trabalhos publicados atualmente se refere à reciclagem de pneus, o objetivo deste trabalho foi desenvolver e caracterizar formulações contendo um tipo de resíduo industrial, proveniente da fabricação de perfis automotivos, à base de copolímero de butadieno e estireno (SBR) para possível aplicação na própria empresa. As composições foram preparadas e caracterizadas pela determinação das propriedades térmicas (calorimetria diferencial de varredura), reológicas (analisador de processamento de borracha), reométricas (reômetria de disco oscilatório), mecânicas (resistência à tração e ao rasgamento), químicas (densidade de ligações cruzadas) e morfológicas (microscopia eletrônica de varredura). Os resultados obtidos para as composições foram comparados aos de uma amostra controle, de mesma composição, que foi fornecida pela empresa geradora do resíduo de SBR. Os resultados mecânicos indicaram que o processo de revulcanização proposto foi efetivo. Os valores dos parâmetros de tensão na ruptura e resistência ao rasgamento foram de 70 e 50%, respectivamente, em relação aos valores encontrados para a amostra controle, indicando a possibilidade do uso desse resíduo em artefatos de menor exigência técnica. The recycling of waste rubber has very important significances, such as protection of the environment and conservation of energy. Considering that most of published works concerning this subject are about tire recycling, the objective of this work was to develop and characterize formulations containing a type of industrial waste, from the manufacture of automotive profiles, based on styrene-butadiene rubber (SBR) for possible application in the industry. The compositions were formulated and characterized by thermal (differential scanning calorimetry), rheological (rubber processor analyzer), rheometrical (oscillatory disc rheomether), mechanical (tensile strength and tear resistance), chemical (cross-link density) and morphological properties (scanning electron microscopy). The results obtained for these compositions were compared to a control sample purchased for the industry, with the same formulation of the SBR scraps. Obtained results show that the revulcanization process was effective. Values for tensile strength and tear resistance were 70 and 50%, respectively, compared to values found for the control sample, indicating the possibility of using this residue as artifacts of lower technical requirement.

Composites of recycled poly(ethylene terephthalate) (PET) and short glass fibers (GFs) in different compositions (0, 20, 30, and 40 wt% of GFs) with optimized microstructures and high mechanical performance were obtained through melt processing. Composites showed appropriate dispersion and distribution and suitable bonding of the GF throughout the PET matrix, using either recycled bottle-grade PET in its degraded form or in a solid-state polymerized (SSP) form and GFs treated with either aminosilane or epoxysilane coupling agents. The high level of reinforcement of these PET/GF composites was confirmed by comparison of the experimental elastic modulus values of PET/GF composites with theoretical ones obtained using the Halpin–Tsai model. An important aspect highlighted by this study is that although it has been stated in the literature that this is only possible with the use of twin-screw extruders, these PET/GF composites with optimized microstructure and with high mechanical performance were compounded using a single-screw extruder with a double-flight barrier screw. In general, slightly better mechanical strengths were achieved for the composites based on the SSP recycled PET, which may be associated with its highly entangled amorphous phase arising from its higher molecular weight.

Este trabalho tem como objetivo a incorporação da mica à matriz do elastômero termoplástico de poliuretano (TPU) tipo poliéter, para o desenvolvimento de novos materiais nos quais as propriedades inerentes da mica possam ser combinadas às do TPU. Este elastômero termoplástico tem alto custo, ao contrário da mica, que é de baixo custo e abundante no Brasil. Os diferentes compósitos, com teores de mica variando de 0 a 20 phr (por cem partes de resina), foram preparados em misturador interno, acoplado a um reômetro de torque Haake. Estes compósitos foram analisados termicamente por análise termogravimétrica (TGA) e análise dinâmico-mecânica (DMA). Foi observado que a incorporação de mica ao TPU altera as propriedades dinâmico-mecânicas bem como a estabilidade térmica deste polímero em diferentes atmosferas. A adição de mica desloca o início da degradação para temperaturas mais baixas nas duas atmosferas (inerte e oxidante) e a temperatura de transição vítrea tem ligeira diminuição com o aumento do teor de mica. Os resultados decorrem principalmente das interações entre a mica e o segmento rígido do TPU, durante o processamento em misturador interno. This work is aimed at incorporating mica to the matrix of a polyether type thermoplastic polyurethane elastomer (TPU), for the development of new materials in which the inherent properties of mica could be combined to those of TPU. This thermoplastic elastomer has high cost, unlike mica, which is inexpensive and abundant in Brazil. The different composites, with the mica contents varying from 0-20 phr (per hundred resin) were prepared in an internal mixer, coupled to a Haake torque rheometer. These composites had their thermal properties analyzed by thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The incorporation of mica caused changes in the thermal stability of TPU in different atmospheres and in its dynamic mechanical properties. The addition of mica shifted the onset of degradation to lower temperatures in the two atmospheres (inert and oxidizing), while the glass transition temperature decreased slightly with increasing mica content. The results stem mainly from the interactions between mica and TPU hard segments during processing in the internal mixer.

This work is concerned with the preparation of thermoplastic polyurethane elastomer (TPU) composites with mica, and their characterization as for processability, mechanical and thermal properties and morphology behavior. The amount of added mica varied from 0 to 20 phr and the results showed few interactions between mica and the polymer matrix. Processability is facilitated by the increasing amount of mica but TPU upon strain crystallizability, as well as Tg, decrease with the increase in mica content. The main interest in using mica is the evaluation of a low cost mineral as a reinforcing material for the engineering polymer TPU. Описаний процес підготовки композитів термопластичного поліуретанового еластомеру (ТПУ) з слюдою, та наведені такі їх характеристики, як технологічність, механічні та теплові властивості і морфологія. Кількість доданої слюди змінювалась від 0 до 20 мас.част. Показана взаємодія між слюдою і полімерною матрицею. Встановлено, що збільшення кількості слюди сприяє технологічності процесу, але при цьому зменшується напруження кристалізованості та температура склування. Показано, що низька вартість мінералу як укріплюю чого матеріалу для технічного полімеру ТПУ є критерієм оцінювання.

In this work, natural rubber (NR) and regenerated cellulose (cel II) latexes were co-coagulated and to the mixture epoxidized natural rubber (ENR) was added on a two-roll mill. The cellulose content was fixed at 20 phr while ENR content varied from 0 to 75 phr. The influence of ENR was studied through the cure characteristics, aging and dynamic-mechanical properties. The aging provides nanocomposites with better solvent resistance and increased tensile strength at ENR content of 25 phr. The results suggest that a new type of light-colored nanocomposites were obtained, which presented high mechanical performance and resistance to solvents.

In this work, nanocomposites of styrene butadiene rubber (SBR), cellulose II, and clay were prepared by cocoagulation of SBR latex, cellulose xanthate, and clay aqueous suspension mixtures. The incorporated amount of cellulose II was 15 phr, and the clay varied from 0 to 7 phr. The influence of cellulose II and clay was investigated by rheometric, mechanical, physicochemical, and morphological properties. From the analysis of transmission electron microscopy (TEM), dispersion in nanometric scale (below 100nm) of the cellulosic and mineral components throughout the elastomeric matrix was observed. XRD analysis suggested that fully exfoliated structure could be obtained by this method when low loading of silicate layers (up to 5 phr) is used. The results from mechanical tests showed that the nanocomposites presented better mechanical properties than SBR gum vulcanizate. Further-more, 5 phr of clay is enough to achieve the best tensile properties

Most condom manufacturers claim a 5 year shelf-life for their products; however, condoms can decay much more rapidly than the reported shelf-life would suggest, because of the uncontrolled storage conditions. For this reason, development of mathematical model to predict condom shelf-life as a function of storage conditions can be very useful. In this work, six brands of condoms were aged under subtropical ambient conditions for 5 years and under accelerated conditions at four temperatures for various times. The changes in burst pressure and burst volume were used as the main indicators of product degradation. Experimental data were analyzed and two mathematical models (both based on the reparameterized Arrhenius equation) were proposed to describe the obtained data. It is shown for the first time that it is possible to estimate and predict the degradation of natural rubber condoms with confidence with the help of the proposed models, based on data obtained from accelerated degradation experiments, provided that different activation energies are used for the burst pressure and volume. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

In this work, sodium montmorillonite clay was added, as filler, to nanocomposites of natural rubber (NR) and cellulose II (regenerated cellulose) in amounts varying from 0 to 5 phr (per hundred resin). Natural rubber (NR)/cellulose II/montmorillonite nanocomposites were prepared by co-coagulating NR latex, montmorillonite aqueous suspension and cellulose xanthate. The clay was previously exfoliated in water, and the resulting suspension was then added to the mixture of NR latex with cellulose xanthate. Morphological, rheometric, mechanical, and dynamic mechanical properties were evaluated, and an increase in these properties was observed upon the addition of cellulose and clay nanomaterials to the rubber matrix. The results show the advantage in using cellulose as a nanopolymer as well as MMT as nanofiller. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

The curing behavior of commercial phenol-formaldehyde novolac resins with hexamethylenetetramine (HMTA) under non-isothermal and isothermal conditions was followed by dynamic rheological measurements. Changes in parameters of the viscoelastic material such as storage modulus (G′) and complex viscosity (η*) during the cure process were evaluated accurately. The isothermal kinetics reaction was described using a phenomenological equation based on the Malkin and Kulichikhin model. The systematic increase in (Ea) values showed that the increase in bulk viscosity during the reaction alters the resin curing process by reducing diffusion of molecules and hindering network growth. Higher HMTA contents lead to faster growing rates in the crosslinking network, hence there are more crosslinked bonds after a shorter period of reaction. This fact implies that active species need more energy to form new crosslinking bonds, changing the curing reaction mechanism.

Natural rubber (NR) isolated from Hevea Brasiliensis was investigated by differential scanning calorimetry, dielectric spectroscopy, and high-pressure dielectric spectroscopy. In the range of frequ...

Epoxidized natural rubber (ENR) samples of various epoxidation degrees were synthesized from natural rubber (NR) latex, and 25 mole% epoxide of ENR was used to prepare ENR room temperature-curable films for coating applications. The films were prepared from rubber solutions. Trimethylolpropane tris(2-mercaptoacetate) (TMP-SH) was used as a curing agent. The effect of the thiol additive on the tensile and thermal properties of epoxidized natural rubber (ENR) was investigated. For the sake of comparison, NR and TMP-SH-containing formulations were also prepared. It was observed that the addition of TMP-SH improved the tensile, thermal and swelling properties of ENR, indicating the formation of crosslinks. On the other hand, the addition of TMP-SH didn't improve the properties of NR, indicating the absence of reaction with TMP-SH. On the basis of data on the properties of the ENR films of this work it is demonstrated that these are appropriate for coating applications.

In this work mica or carbon black were used as filler in composites of acrylic rubber (ACM). The fillers differ not only in nature, mica being a mineral material and carbon black being organic, but also in form and particle size. The content of filler varied from 0 to 50 phr and its influence on ACM was evaluated based on cure parameters, mechanical, and swelling properties. The cure parameters allow the conclusion that the presence of mica does not have a negative effect on the cure or processability; the swelling results indicated a weak interaction between ACM and mica even though the mechanical properties of ACM composition with 40 phr of mica were found to be similar to those of 20 phr carbon black. As a result of mica being less expensive than carbon black, is light colored and easily processible, these properties are of industrial importance. All properties analyzed were compared with gum type composition (without filler).

The processing characteristic of blends of poly(vinylidene fluoride) (PVDF) and poly(methyl methacrylate) (PMMA), in different compositions, were studied by torque rheometry. The polymers were mixed in a batch mixer in proportions of 20, 40, 60 and 80% by weight of PVDF, at 190 °C using rotor speeds of 30, 60 and 100 rpm. The results have shown that the increase of the PMMA content improved the processability of the blends, in spite of an increase of the activation energy of flow. Higher speeds of blending caused a reduction of the homogenization blending times of the blends. The PMMA processing at different speeds studied by parallel plate rheometer showed that a similar behavior and did not affect considerably the degradation of PMMA, according the Carreau model.

Mechanical recycling of vulcanized rubber scraps is a low-cost alternative in the search for the recovery of this kind of industrial solid waste. The aim of this study is to incorporate styrene–butadiene rubber (SBR) industrial scraps into a base formulation of SBR used in the fabrication process of extruded profiles. Rheometric, mechanical and morphological characteristics of this base formulation with industrial scrap powder (SBR-r) added as filler were evaluated. Eight composites with different proportions, varying from 10 to 80 phr (parts for hundred of rubber) of SBR-r were prepared and the results were compared with the control sample (base formulation with 0 phr of SBR-r). The results indicated that the incorporation of rubber powder did not significantly affect the cure characteristics of the composites. The mechanical properties such as tensile and tear strength showed that up to 50 phr of SBR-r can be added without adversely affecting these properties. Micrographs corroborated the mechanical results, indicating the homogeneity of the scraps in the elastomeric matrix.

Poly(ethylene terephthalate) (PET) composites containing muscovite mica as reinforcing filler were prepared by melt mixing, and their molecular dynamics were investigated by low-field NMR. Spin-lattice and proton spin–spin relaxation times of composites containing different amounts of the filler from 2 to 15 wt% were evaluated and the results compared with pure PET. DSC showed that for systems containing muscovite mica in percentages above 2 wt% a high level of crystallinity is achieved. By proton spin-lattice relaxation studies, a slight decrease in the T1H is observed for the composites with filler content up to 8 wt% and a drastic decrease at the higher filler content (15 wt%). Changes in T1H were associated with the content of amorphous phase in the composite.

The problem of vulcanized rubber scraps is of high importance nowadays, and the revulcanization of these scraps is an alternative to reutilize them. This work concerns the investigation of the processability of new compositions made from revulcanizable rubber scraps, through data from the Haake torque rheometer and the Rubber Process Analyzer (RPA). By varying cure system and oil addition, powdered butadiene-styrene rubber compositions (SBR-r) scraps were used in the preparation of six formulations. A control composition of identical formulation as the scraps was supplied by the industry and analyzed in all situations. Data reveal that new products can be produced by the reutilization of these industrial scraps.

SBR and EPDM extruded profile scraps are ground under ambient conditions for further utilization in recycling and reclaiming processes. The obtained powders (SBR-r and EPDM-r, respectively) are physically, thermally, and chemically characterized and the results are analyzed as for its suitability for reuse methods. It is possible to obtain powdered SBR and EPDM rubber with irregular shape and high surface roughness. The grinding process has not deteriorated the material. The obtained powder is suitable for utilization in new formulations and in regeneration processes.

This work is concerned with the influence of mica in natural rubber compounds on properties such as Mooney viscosity, processability and rheological behavior. The amount of this filler was varied from 0 to 40 phr and the stabilized and totalized torques, specific and mechanical energies were determined in a HAAKE torque rheometer. The elastic torque (S′) and complex dynamic viscosity (η∗) were measured on a rubber processing analyzer (RPA). The results show that mica influences processability and rheological properties, by acting as a processing agent in natural rubber composites.

Composites of recycled poly(ethylene terephthalate) (PET) reinforced with short glass fiber (GF) (0, 20, 30, and 40 wt %) were compounded in a single-screw extruder (SSE) and in a intermeshing corotating twin-screw extruder (TSE). An SSE fitted with a barrier double-flight screw melting section in between two single-flight sections and a TSE with a typical screw configuration for this purpose were used. The composites were subsequently injection molded at two different mold temperatures (10 and 120°C), with all other operative molding parameters kept constant. The effects of processing conditions on composite microstructure, PET degree of crystallinity, and composite mechanical properties were evaluated. Appropriate dispersive and distributive mixing of the glass fiber throughout the PET matrix as well as fine composite mechanical and thermal-mechanical properties were achieved regardless of whether the composites were prepared in the SSE or TSE. The performance of the SSE was attributed to the efficiency of the barrier screw melting section in composite mixing. The mold temperature influenced the mechanical properties of the composites, by controlling of the degree of crystallinity of the PET in the composites. For a good balance of mechanical and thermal-mechanical properties, high mold temperatures are desirable, typically, 120°C for a mold cooling time of 45 s. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Nanocomposites of nitrile rubber (NBR) and cellulose II (Cel II) were prepared by co-coagulation of nitrile rubber latex and cellulose xanthate mixtures. The effect of the addition of increasing amounts of Cell II, varying from 0 to 30 phr, on the mechanical behavior of a NBR was analyzed. The fracture mechanisms of the nitrile rubber-cellulose II (NBR/Cel II) nanocomposites after tension and tear tests was investigated by scanning electron microscopy (SEM) and correlated to the test results. It was found that the addition of Cell II to NBR leads to a gradual change in the stress at break, and the samples with 20 phr of Cel II showed the highest resistance; as the cellulose content is increased to 30 phr, the strain at break decreases. The SEM fractographic analyses of NBR/Cel II nanocomposites, with cellulose content up to 30 support the observed mechanical behavior of the material. The results are presented and discussed. The obtainment of NBR/Cel II nanocomposites was proven by transmission electron microscopy (TEM).

Nanocomposites of butadiene-acrylonitrile copolymer (NBR) and cellulose II were obtained from mixtures of nitrile rubber latex and cellulose xanthate by using a co-coagulation system. The influences of low and medium acrylonitrile content in NBR and the cellulose II content, varying from 0 to 30 phr, were investigated by means of rheometric and equilibrium swelling experiments. The cure parameters obtained from the Oscillating Disk Rheometer data were utilized to characterize the structure of cellulose II present in the rubber vulcanizates through Wolff’s equation. The swelling experiments were analyzed by using Flory-Rehner theory and Kraus and Cunneen-Russel equations to evaluate the NBR-Cel II interaction. From the results it was possible to conclude that cellulose II promotes a positive influence on cure parameters and crosslinking formation. It was also observed that the high butadiene content in NBR facilitated the interaction rubber-cellulosic component. The dispersion and distribution of cellulose in NBR matrix gave rise to nanomaterials, as observed by transmission electron microscopy.

The influences of elastomer ratio and preparation mode on the degradation behavior of NR/BR Natural rubber and polybutadiene rubber blends were investigated by using non-isothermal thermogravimetric analysis (TGA). The activation energy for the degradation process was determined by using both the Ozawa and the Kissiger methods, none of them requiring the knowledge of the reaction mechanism. TGA shows that degradation of NR/BR blends takes place in two steps.

Most condom manufacturers claim a 5-year shelf life. A predictive test for condom shelf life is needed, because products shipped to tropical climates have decayed much more rapidly than the stated shelf life would suggest. In this work, five brands of condoms were aged under ambient conditions for 5 years, and in an oven at 50 and 70 °C for various times up to 182 days. The inflation test was used as an indicator of the condom quality. Burst volume and pressure under ambient conditions and after oven conditioning were compared, at various time points, in order to find an optimum combination of temperature and time to predict shelf life using elevated temperature accelerated aging. It was shown that aging at 50 °C provides some predictive information about shelf life, but aging at 70 °C is not as useful.