Effects of benzoyl peroxide on some properties of composites based on hemp and natural rubber

Degradation by Electron Beam Irradiation of Some Composites Based on Natural Rubber Reinforced with Mineral and Organic Fillers

Composites based on natural rubber reinforced with mineral (precipitated silica and chalk) and organic (sawdust and hemp) fillers in amount of 50 phr were obtained by peroxide cross-linking in the presence of trimethylolpropane trimethacrylate and irradiated by electron beam in the dose range of 150 and 450 kGy with the purpose of degradation. The composites mechanical characteristics, gel fraction, cross-linking degree, water uptake and weight loss in water and toluene were evaluated by specific analysis. The changes in structure and morphology were also studied by Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy. Based on the results obtained in the structural analysis, possible mechanisms specific to degradation are proposed. The increasing of irradiation dose to 450 kGy produced larger agglomerated structures, cracks and micro voids on the surface, as a result of the degradation process. This is consistent with that the increasing of irradiation dose to 450 kGy leads to a decrease in crosslinking and gel fraction but also drastic changes in mechanical properties specific to the composites’ degradation processes. The irradiation of composites reinforced with organic fillers lead to the formation of specific degradation compounds of both natural rubber and cellulose (aldehydes, ketones, carboxylic acids, compounds with small macromolecules). In the case of the composites reinforced with mineral fillers the degradation can occur by the cleavage of hydrogen bonds formed between precipitated silica or chalk particles and polymeric matrix also.

Modification of Fibres and Matrices in Natural Fibre Reinforced Polymer Composites: A Comprehensive Review

Composite materials derived from eco-friendly natural fibres and other biodegradable materials have gained prominence in industrial applications due to their sustainability and reduced greenhouse gas emissions attributes in comparison with conventional reinforcements such as glass and carbon fibres. Application of natural fibre-polymer composites (NFPCs) in different industrial applications provides competitive edge due to its lightweight, higher specific mechanical properties than glass fibres, sustainability and lesser cost involved in production. There are certain challenges associated with natural fibers and its reinforcement in composites such as poor bonding between the fibres and matrix due to its contradictory nature of characteristics, moisture absorption, lower thermal properties and poor interfacial adhesion between the natural fibre and polymer matrix. The challenges involved in NFPCs needs to be overcome to produce materials with relatively equivalent properties to that of conventional compositesand other metallic structures. Several researchers around the globe have conducted investigations with the primary attention being paid to the modification of natural fibers and matrix by employing surface treatments and other chemical treatment methods. In order to address the need for eco-friendly and sustainable materials in different domains, a comprehensive review on natural fibers and its sources, available matrix materials, modification techniques, mechanical and thermal properties of NFPCs is needed for better understanding of behavior of NFPCs.This work provides the information and wholistic view of natural fibre reinforced composites based on the results obtained from modification techniques,with the view of focusing the review in terms of different chemical and physical treatment techniques, modification of fibers and matrix and enhanced mechanical and thermal properties in the composites. This article is protected by copyright. All rights reserved.

Advancement in hemp fibre polymer composites: a comprehensive review

Natural fibres as reinforcement for composite materials have witnessed a resurgence of interest in the past few years, largely due to ecological concerns, legislative directives and technological advancements. Hemp is one of the most popular natural fibres used as reinforcement in polymers owing to its superior mechanical properties. At present, hemp fibres have attracted the global interest of design engineers for developing composites having extensive applications in automobiles, electrical, construction and packaging industries. Although several literatures explore different aspects of hemp fibre reinforced composites, there is no proper literature that summarizes the surface treatment, processing techniques, mechanical performance and hybridization of hemp fibre composites. This review is envisioned to put forth a comprehensive summary of the research work published in the field of hemp fibre reinforced composites with special reference to the structure of hemp fibres, different methods for surface modification and processing techniques to fabricate the composites based on thermoplastic, thermoset and biopolymers. The paper also focuses on the effects of surface treatment on the mechanical performance of the composites.

Hemp and Its Derivatives as a Universal Industrial Raw Material (with Particular Emphasis on the Polymer Industry)-A Review

This review article provides basic information about cannabis, its structure, and its impact on human development at the turn of the century. It also contains a brief description of the cultivation and application of these plants in the basic branches of the economy. This overview is also a comprehensive collection of information on the chemical composition of individual cannabis derivatives. It contains the characteristics of the chemical composition as well as the physicochemical and mechanical properties of hemp fibers, oil, extracts and wax, which is unique compared to other review articles. As one of the few articles, it approaches the topic in a holistic and evolutionary way, moving through the plant’s life cycle. Its important element is examples of the use of hemp derivatives in polymer composites based on thermoplastics, elastomers and duroplasts and the influence of these additives on their properties, which cannot be found in other review articles on this subject. It indicates possible directions for further technological development, with particular emphasis on the pro-ecological aspects of these plants. It indicates the gaps and possible research directions in basic knowledge on the use of hemp in elastomers.

Polydimethylsiloxane Elastomers Filled with Rod-Like α-MnO2 Nanoparticles: An Interplay of Structure and Electrorheological Performance

For the first time, electroactive nanocomposite elastomers based on polydimethylsiloxane and filled with rod-like α-MnO2 nanoparticles have been obtained. The curing of the filled elastomer in an electric field, resulting in the ordering of the α-MnO2 particles, had a significant effect on the degree of polymer crosslinking, as well as on the electrorheological characteristics of the nanocomposites obtained through this process, namely the values of the storage and loss moduli. The dielectric spectra of filled elastomers in the frequency range 25-106 Hz were analysed in terms of interfacial relaxation processes. It has been shown, for the first time, that the application of an electric field leads to a decrease in the value of the Payne effect in composite elastomers. Analysis of the rheological effect in the obtained materials has demonstrated the possibility of designing highly efficient electrorheological elastomers that change their elastic properties by 4.3 times in electric fields of up to 2 kV/mm.

Water Absorption Kinetics in Natural Rubber Composites Reinforced with Natural Fibers Processed by Electron Beam Irradiation

Natural rubber composites reinforced with hemp, flax, and wood sawdust were obtained by irradiation at room temperature with an electron beam of 5.5 MeV in order to meet the actual need for new materials that are environmentally friendly and safe for human health. The natural fibers loading was between 5 and 20 phr and the processing doses were between 75 and 600 kGy. The kinetics of water absorption in these materials were studied. The water diffusion was analyzed through Fick’s law. The water absorption parameters (Qt and Qeq), diffusion parameters (k and n), diffusion coefficient (D), intrinsic diffusion coefficient (D*), sorption coefficient (S), and permeation coefficient (P) have depended on the fiber nature, amount used in blends, and irradiation dose. The obtained results showed that not in the case of each type of fiber used, the water absorption could be correlated with the specific cellulose and hemicellulose content, due to the changes induced by the electron beam.

Electrorheological Properties of Polydimethylsiloxane/TiO2-Based Composite Elastomers

Electrorheological elastomers based on polydimethylsiloxane filled with hydrated titanium dioxide with a particle size of 100-200 nm were obtained by polymerization of the elastomeric matrix, either in the presence, or in the absence, of an external electric field. The viscoelastic and dielectric properties of the obtained elastomers were compared. Analysis of the storage modulus and loss modulus of the filled elastomers made it possible to reveal the influence of the electric field on the Payne effect in electrorheological elastomers. The elastomer vulcanized in the electric field showed high values of electrorheological sensitivity, 250% for storage modulus and 1100% for loss modulus. It was shown, for the first time, that vulcanization of filled elastomers in the electric field leads to a significant decrease in the degree of crosslinking in the elastomer. This effect should be taken into account in the design of electroactive elastomeric materials.

New Materials Based on Ethylene Propylene DieneTerpolymerand Hemp Fibers Obtained by Green Reactive Processing

The paper presents the obtaining of new green polymeric composites using a sustainable reactive processing method, namely electron beam irradiation. EPDM rubber mixtures were reinforced with different amounts of short hemp fibers, which were then irradiated at doses between 75 and 600 kGy. The samples were analyzed by determination of physical-mechanical properties, sol-gel analysis, crosslink density (using the well-known modified Flory-Rehner equation for tetra functional networks), determination of rubber-fiber interactions (using the Kraus equation), water uptake test and FTIR analysis. The obtained results indicate an improvement of the hardness, the tensile and tear strength as the quantity of hemp fibers increases. As the irradiation dose increases, there is an increase in the degree of crosslinking and the gel fraction. Analyzing the behavior of the irradiation samples using the Charlesby-Pinner equation, it is observed that all the samples tend to crosslink by irradiation, the share of degradation reactions being low. For these reasons, the new materials can be used in the food, pharmaceutical or medical field, because the obtained products are sterile and can be easily resterilized by irradiation. They have high elasticity values and can be used to make packaging, seals and other consumer goods.

P. SH, N. S, V. S, Balan AK, E. P. Polyaniline modified lignocellulosic fibers from sago seed shell powder for electrochemical devices

We report the development of a novel electrode material from agrarian waste, sago (Cycas circinalis) seed shell powder (SSP). Lignocellulosic fibers obtained from sago seed shell powder were modified with polyaniline (PANI) by an in situ oxidative polymerization technique. Morphological changes, thermal stability and crystallinity of modified SSP were investigated using FTIR, XRD, SEM, TGA and DSC techniques. The structural organization of SSP with the monomer of PANI significantly influenced the thermal and electrical properties of resulting PANI-SSP composite material. The developed PANI-SSP composite showed enhanced thermal stability up to 308 °C with appreciable dc-conductivity in the range of 10⁻¹ S cm⁻¹ having very low activation energy of 0.0153 eV. The I–V characteristics of the composite exhibited nonohmic behaviour similar to a diode. Thus, the chemical modification of lignocelluloses fibers opens up a new avenue for fabricating cheap, eco-friendly substrates for energy storage devices, disposable electronic applications and diverse scopes for research and development.

We report the development of a novel electrode material from agrarian waste, sago (Cycas circinalis) seed shell powder (SSP).