Study on the efficiency of a transducer for sonochemistry by calorimetry

Sonochemistry is an effective method for initiation or enhancement of the chemical reactions by ultrasound in a wide range of applications. In this study, the efficiency of a sonochemistry transducer, defined as the ratio of ultrasonic power to electrical power, was investigated for different materials and the thicknesses of the vibration plate in the frequency range 22 kHz–2 MHz. The ultrasonic power was measured by calorimetry. To eliminate the influence of reflected waves, the transducer was attached to the side of a cylindrical vessel. The transducer with a stainless-steel vibration plate was more efficient than those with vibration plates of acrylonitrile butadiene styrene plastic or chloroprene rubber. The efficiencies of the transducers also increased with decreasing thickness of the vibration plates. Langevin-type transducers were less efficient than the disk-type transducers.

Enhancing material performance of Chloroprene rubber (CR) by strategic incorporation of zirconia

Chloroprene rubber (CR) composites, embedded with a well dispersed zirconia, within it’s matrix are produced that combine superior reinforcement of zirconia with the other useful composite properties. The in-situ incorporated...

Theoretical and Experimental investigation of PVMQ/ EPDM-g-MA/CR blends: Rheological, Compatibility and Mechanical Properties

The main problem of uncompatibilize rubbers nano-composites in polymeric matrix are accumulation and agglomeration of graphene oxide. In this study, EPDM-g-MA was used as a compatibilizer for better dispersion of graphene oxide (GO) in the phenyl-vinyl-methyl-polysiloxane/chloroprene rubber (PVMQ/CR) matrix. To achieve this purpose mechanical characterizations, rheology, morphology and curing characterizations of nano-composite was investigated. SEM and TEM were used to assess surface characteristics, morphology and dispersion of EPDM-g-MA in PVMQ/CR nano-composite, which showed the size of EPDM-g-MA in the blends became smaller, denser and more uniform. Also, the results showed that, by increasing the GO nano-platelets in PVMQ/CR matrix during the reaction with EPDM-g-MA, curing properties was improved such a way that optimum curing time and scorch time were decreased and also MH–ML and cure rate index (CRI) were increased and also toughness strength enhanced. In addition, the mechanical properties indicated that tensile strength, fatigue strength, hardness, elongation-at-break and modulus increased by the incorporation with GO nano-platelets.

The Use of Copper Oxides as Cross-Linking Substances for Chloroprene Rubber and Study of the Vulcanizates Properties. Part II. The Effect of Filler Type on the Properties of CR Products

The properties of rubber materials are dependent on the characteristics of the elastomer matrix, the filler type, the cross-linking agent, the number of ingredients, and their interactions. In the previous article, we showed that chloroprene rubber can be efficiently cross-linked with copper(I) oxide or copper(II) oxide. During the processing of rubber compounds, the incorporation of a filler and a curing substance are two substantial parameters, such as the homogeneity of mixing and cross-linking that significantly affect the properties of the vulcanizates. Therefore, this work aimed to evaluate the curing characteristics, mechanical and dynamical properties, morphology, and flammability of the composites containing chloroprene rubber cross-linked with Cu2O or CuO and filled with different fillers (silica, carbon black, montmorillonite, kaolin, chalk). It was found that the type of filler and curing agent had a significant impact on the degree of cross-linking of the chloroprene rubber and the properties of its vulcanizates. The degree and speed of the cross-linking of filled CR were higher when the CR was cured with copper(II) oxide. Among the fillers used, the presence of carbon black or silica ensured the highest degree of CR cross-linking and the most useful properties. The flammability tests indicated that all produced vulcanizates were characterized by a high oxygen index, which allows them to be classified as non-flammable materials.

Novel Crosslinking System for Poly-Chloroprene Rubber to Enable Recyclability and Introduce Self-Healing

The introduction of dynamic bonds capable of mediating self-healing in a fully cross-linked polychloroprene network can only occur if the reversible moieties are carried by the cross-linker itself or within the main polymer backbone. Conventional cross-linking is not suitable for such a purpose. In the present work, a method to develop a self-healable and recyclable polychloroprene rubber is presented. Dynamic disulfide bonds are introduced as part of the structure of a crosslinker (liquid polysulfide polymer, Thiokol LP3) coupled to the polymer backbone via thermally initiated thiol-ene reaction. The curing and kinetic parameters were determined by isothermal differential scanning calorimetry and by moving die rheometer analysis; tensile testing was carried to compare the tensile strength of cured compound, healed compounds and recycled compounds, while chemical analysis was conducted by surface X-Ray Photoelectron Spectroscopy. Three formulations with increasing concentrations of Thiokol LP-3 were studied (2, 4, 6 phr), reaching a maximum ultimate tensile strength of 22.4 MPa and ultimate tensile strain of 16.2 with 2 phr of Thiokol LP-3, 11.7 MPa and 10.7 strain with 4 phr and 5.6 MPa and 7.3 strain with 6 phr. The best healing efficiencies were obtained after 24 h of healing at 80 °C, increasing with the concentration of Thiokol LP-3, reaching maximum values of 4.5% 4.4% 13.4% with 2 phr, 4 phr and 6 phr, respectively, while the highest recycling efficiency was obtained with 4 phr of Thiokol LP-3, reaching 11.2%.

The Use of Copper Oxides as Cross-Linking Substances for Chloroprene Rubber and Study of the Vulcanizates Properties. Part I

The purpose of this work was to verify the ability to cross-link the chloroprene rubber (CR) by using copper oxides: copper(I) oxide or copper(II) oxide. The use of copper oxides arises from the need to limit the application of ZnO as a cross-linking agent of CR. The obtained results indicate that CR compositions cross-linked with copper oxides are characterized by good mechanical properties and a high cross-linking degree. The results show that the type and the amount of copper oxides influence the cross-linking of the CR and the properties of the vulcanizates. For compositions containing copper(II) oxide, the properties are linearly dependent on the amount of CuO. Such a relationship is difficult to notice in the case of the use of copper(I) oxide—when analyzing individual parameters, the best results are obtained for different samples. Infrared spectroscopy (IR) studies confirmed the possibility of cross-linking of chloroprene rubber with copper oxides. This is evidenced by the characteristic changes in the intensity of the bands. Structural changes in the material during heating were determined by the thermal analysis—differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Regardless of the type and amount of copper oxide, all compositions exhibit similar characteristics, and there are no significant changes in the glass transition temperature of the material.

Influence of different curing regimes on properties of new copolymer of chloroprene and acrylonitrile

The curing system plays a vital role in designing rubber compounds for various industrial applications. Therefore, it is paramount to establish viable curing strategies for any new elastomer to explore its application potentials and commercial significance. Impacts of different curing regimes on the properties of a recently developed copolymer of chloroprene and acrylonitrile (acrylonitrile-chloroprene rubber, NCR) are reported here. Several primary accelerators (four from thiourea- and one from thiazolene product families) were used for curing the new rubber along with fixed loadings of zinc oxide (5 phr) and magnesium oxide (4 phr). Besides, curatives based on sulfur and peroxide were also evaluated. The influence of different curing systems on the rheological and physical properties of the copolymer was explored. It has been seen that the properties of the copolymer are considerably influenced by the different curing systems used. While ethylene thiourea (ETU) and propylene thiourea (PTU), as primary accelerators, provide the highest state of cure but may cause scorch. The use of trimethyl thiourea (TMU), on the other hand, results in the fastest rate and the most stable state of cure, good scorch safety, bin stability, and an overall good balance of properties. The sulfur-based crosslinking system induces good mechanical properties but causes limited bin stability, poor high-temperature compression set, and impaired heat resistance properties. As a curing agent, peroxide delivers the best bin stability in the rubber stocks but yields higher stiffness and limited aging resistance in the vulcanizates.

Identification of glycerol as a novel accelerator for sulphur vulcanization of unsaturated rubbers

Different organic polyols were investigated as accelerators for different type of vulcanization system such as sulphur, metal oxide, peroxide with different rubbers such as natural rubber (NR), styrene butadiene rubber (SBR), butadiene rubber (BR), butyl rubber (IIR), nitrile rubber (NBR) and chloroprene rubber (CR). Among all the polyols studied, glycerol found to be the most efficient accelerator for sulphur vulcanization of unsaturated rubbers. Moreover, from rheometric study glycerol was found to be reversion free and scorch safe accelerator. A detailed study was performed with glycerol for sulphur vulcanization of silica filled, SBR + BR-based standard passenger car radial (PCR) tire tread compound and plausible mechanism of acceleration was proposed. Finally, from the PCR tyre tread compound 70% of conventional accelerators, namely N-cyclohexyl-2-benzothiazole sulfenamide (CBS) and di-phenyl guanidine (DPG) were replaced with 5 phr (parts per hundred gram of rubber) of glycerol and properties of the vulcanized compounds were measured. The results evidenced that glycerol could efficiently replace 70% conventional accelerators (CBS + DPG), with additional improvement of scorch time by 68%, tensile strength by 31.5%, elongation at break by 75.6% and tear strength by 9.4% of the PCR tyre tread compound. The increase in mechanical properties was due to the improvement in compatibility between silica and rubber in presence of glycerol. Moreover, glycerol is an environmentally benign (nitrogen free, halogen free), fossil free, low-cost material.