Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 20
Filtrar
Mais filtros

Base de dados
Tipo de documento
Intervalo de ano de publicação
1.
Biomater Adv ; 162: 213921, 2024 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-38870740

RESUMO

Eco-friendly nanotechnology-enabled biopolymers are one of the novel concepts of packaging materials to substitute traditional synthetic polymers and their composites. This article succinctly reviews the recent developments of introducing additional functionalities to biopolymers using metal and metal oxide nanoparticles. The functionality of metal nanoparticles such as silver, zinc oxide, titanium dioxide, copper oxide, gold, and magnesium oxide, as food packaging materials were discussed. The addition of nanoparticles in biopolymers improves mechanical properties, gas barrier properties, durability, temperature stability, moisture stability, antimicrobial activity, antioxidant property, and UV absorbance and can prevent the presence of ethylene and oxygen, hence extending the shelf life of foodstuffs. Other than this, the functional activity of these biopolymer composite films helps them to act like smart or intelligent packaging. The selection of metal nanoparticles, particle migration, toxicological effect, and potential future scope in the food packaging industry are also reviewed.


Assuntos
Embalagem de Alimentos , Nanopartículas Metálicas , Embalagem de Alimentos/métodos , Biopolímeros/química , Nanopartículas Metálicas/química , Nanocompostos/química , Humanos , Antioxidantes/química , Antioxidantes/farmacologia
2.
Int J Biol Macromol ; 255: 128004, 2024 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-37979737

RESUMO

Cellulose nanofibers have been extracted from arecanut palm sheath fibers via mild oxalic acid hydrolysis coupled with steam explosion technique. Cellulose nanofibers with diameter of 20.23 nm were obtained from arecanut palm sheath fibers. A series of robust hydrophobic cellulose nanopapers were fabricated by combining the synergistic effect of surface roughness induced by the successful deposition of zinc oxide (ZnO) nanoflakes and stearic acid modification via a simple and cost-effective method. In this work, agro-waste arecanut palm sheath was employed as a novel source for the extraction of cellulose nanofibers. 2 wt% of ZnO nanoflakes and 1 M concentration of stearic acid were used to fabricate mechanically robust hydrophobic cellulose nanopapers with a water contact angle (WCA) of 134°. During the deposition of zinc oxide nanoflakes on the CNP for inducing surface roughness, a hydrogen bonding interaction is formed between the hydroxyl groups of cellulose nanofibers and the zinc oxide nanoflakes. When this surface roughened CNP was dipped in stearic acid solution. The hydroxyl groups in zinc oxide nanoflakes undergoes esterification reaction with carboxyl groups in stearic acid solution forming an insoluble stearate layer and thus inducing hydrophobicity on CNP. The fabricated hydrophobic cellulose nanopaper displayed a tensile strength of 22.4 MPa and better UV blocking ability which is highly desirable for the sustainable packaging material in the current scenario. Furthermore, the service life of the pristine and modified cellulose nanopapers was predicted using the Arrhenius equation based on the tensile properties obtained during the accelerated ageing studies. The outcome of this study would be broadening the potential applications of hydrophobic and mechanically robust cellulose nanopapers in sustainable packaging applications.


Assuntos
Nanofibras , Óxido de Zinco , Óxido de Zinco/química , Celulose/química , Embalagem de Produtos , Nanofibras/química , Interações Hidrofóbicas e Hidrofílicas
3.
Carbohydr Polym ; 310: 120700, 2023 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-36925259

RESUMO

This research highlights the synergistic use of carbon black (CB) and chitin nanofibers (CHNFs) for developing green tyres for the first time. The CHNFs (12-30 nm) were prepared from chitin powder with the help of steam explosion and mild oxalic acid hydrolysis. The CHNFs were uniformly dispersed in natural rubber (NR) latex, dried, and mixed with CB in a two-roll mill to form NR/CB/CHNF composites. The NR/CB/CHNF composite at 1 phr CHNF loading exhibited tensile and tear strengths that were about 47 and 160 % greater than the NR-Neat, respectively. The dynamic mechanical analysis showed that the loss tangent (tan δ) at 60 °C was 50 % lower for the NR/CB/CHNF 1.0 composite than for the NR/CB50 composite. The study succeeded in developing a new green tyre tread formulation that would be helpful for attaining sustainability and a circular economy.

4.
Molecules ; 27(22)2022 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-36432134

RESUMO

Recently, considerable interest has been focused on developing greener and biodegradable materials due to growing environmental concerns. Owing to their low cost, biodegradability, and good mechanical properties, plant fibers have substituted synthetic fibers in the preparation of composites. However, the poor interfacial adhesion due to the hydrophilic nature and high-water absorption limits the use of plant fibers as a reinforcing agent in polymer matrices. The hydrophilic nature of the plant fibers can be overcome by chemical treatments. Cellulose the most abundant natural polymer obtained from sources such as plants, wood, and bacteria has gained wider attention these days. Different methods, such as mechanical, chemical, and chemical treatments in combination with mechanical treatments, have been adopted by researchers for the extraction of cellulose from plants, bacteria, algae, etc. Cellulose nanocrystals (CNC), cellulose nanofibrils (CNF), and microcrystalline cellulose (MCC) have been extracted and used for different applications such as food packaging, water purification, drug delivery, and in composites. In this review, updated information on the methods of isolation of nanocellulose, classification, characterization, and application of nanocellulose has been highlighted. The characteristics and the current status of cellulose-based fiber-reinforced polymer composites in the industry have also been discussed in detail.


Assuntos
Celulose , Nanopartículas , Celulose/química , Tecnologia , Nanopartículas/química , Embalagem de Alimentos , Fenômenos Químicos
5.
Sci Rep ; 12(1): 20580, 2022 11 29.
Artigo em Inglês | MEDLINE | ID: mdl-36446817

RESUMO

A novel bio adsorbent was fabricated from turmeric, polyvinyl alcohol and carboxymethyl cellulose for MB dye removal. The physicochemical, antibacterial and biodegradable nature of the film was evaluated using scanning electron microscopy, optical microscopy, universal testing machine, water contact angle, thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, agar disc diffusion method and soil degradability. The inclusion of turmeric into PVA/CMC film improves the biodegradability, antibacterial activity and thermomechanical property of the films. PVA/CMC/TUR film displayed good MB adsorption capacity (qe: 6.27 mg/g) and maximum dye adsorption (R%; 83%) and was achieved at initial dye concentration of 10 mg/L with contact time 170 min at room temperature. The adsorption data of MB on PVA/CMC/TUR film was evaluated using four models Langmuir, Freundlich, Temkin and D-R isotherms. The different kinetic of adsorption (pseudo-first order, pseudo-second order and intraparticle diffusion model) was also applied for adsorption of MB on the films. The experimental result suggests that PVA/CMC/TUR films are an alternate cheap adsorbent for water treatment.


Assuntos
Azul de Metileno , Filmes Cinematográficos , Adsorção , Curcuma , Microscopia Eletrônica de Varredura , Antibacterianos
6.
Int J Biol Macromol ; 209(Pt B): 1745-1759, 2022 Jun 01.
Artigo em Inglês | MEDLINE | ID: mdl-35469954

RESUMO

Nanocellulose is the "green magnet" which attracts a wide spectrum of industries towards it due to its availability, biodegradability, and possible smart applications. For the first time, pineapple pomace was being explored as an economic precursor for cellulose nanofibers. Nanofiber isolation was accomplished using a chemo-mechanical method and solution casting was adopted for the development of nanopapers. Moreover, the study examines the structural, optical, crystalline, dimensional, and thermal features of nanofibers isolated using different acid hydrolysis (oxalic acid and sulphuric acid) methods. Fourier-transform infra-red spectroscopy, 13C solid-state nuclear magnetic resonance spectroscopy, and X-ray diffraction analysis indicated the presence of type I cellulose. The transmittance, crystallinity index, and thermal stability of PPNFS (sulphuric acid treated fiber) were greater than PPNFO (oxalic acid treated fiber). The transmission electron microscopy and dynamic light scattering analysis confirmed the nanodimension of PPNFO and PPNFS. While comparing the optical and mechanical properties of nanopapers, PPNFS outperforms PPNFO. The tensile strength of the prepared nanopapers (64 MPa (PPNFO) and 68 MPa (PPNFS)) was found to be high compared to similar works reported in the literature. The prepared nanopaper is proposed to be used for food packaging applications.


Assuntos
Ananas , Nanofibras , Celulose/química , Hidrólise , Nanofibras/química , Ácido Oxálico , Ácidos Sulfúricos
7.
Int J Biol Macromol ; 206: 92-104, 2022 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-35217088

RESUMO

This study aims to extract cellulose nanofibers (CNFs) from a sustainable source, i.e. millet husk, which is an agro-waste worthy of consideration. Pre-treatments such as mercerisation, steam explosion, and peroxide bleaching (chlorine-free) were applied for the removal of non-cellulosic components. The bleached millet husk pulp was subjected to acid hydrolysis (5% oxalic acid) followed by homogenization to extract CNFs. The extracted CNFs were characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Dynamic Light Scattering (DLS), Energy Dispersive X-ray Spectroscopy (EDX), Thermogravimetry (TG and DTG), Differential scanning calorimetry (DSC), and Solid state 13C nuclear magnetic resonance spectroscopy (solid state 13C NMR). The isolated CNFs show a typical cellulose type-I structure with a diameter of 10-12 nm and a crystallinity index of 58.5%. The appearance of the specific peak at 89.31 ppm in the solid state 13C NMR spectra validates the existence of the type-I cellulose phase in the prepared CNFs. The prepared CNFs had a maximum degradation temperature (Tmax) of 341 °C, that was 31 °C greater than raw millet husk (RMH). The outcome of the study implies that the nanofibers are prominent alternatives for synthetic fibers for assorted potential applications, especially in manufacturing green composites.


Assuntos
Nanofibras , Pennisetum , Celulose/química , Milhetes , Nanofibras/química , Espectroscopia de Infravermelho com Transformada de Fourier , Termogravimetria
8.
Polymers (Basel) ; 14(2)2022 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-35054672

RESUMO

Epoxy resins as important organic matrices, thanks to their chemical structure and the possibility of modification, have unique properties, which contribute to the fact that these materials have been used in many composite industries for many years. Epoxy resins are repeatedly used in exacting applications due to their exquisite mechanical properties, thermal stability, scratch resistance, and chemical resistance. Moreover, epoxy materials also have really strong resistance to solvents, chemical attacks, and climatic aging. The presented features confirm the fact that there is a constant interest of scientists in the modification of resins and understanding its mechanisms, as well as in the development of these materials to obtain systems with the required properties. Most of the recent studies in the literature are focused on green fillers such as post-agricultural waste powder (cashew nuts powder, coconut shell powder, rice husks, date seed), grass fiber (bamboo fibers), bast/leaf fiber (hemp fibers, banana bark fibers, pineapple leaf), and other natural fibers (waste tea fibers, palm ash) as reinforcement for epoxy resins rather than traditional non-biodegradable fillers due to their sustainability, low cost, wide availability, and the use of waste, which is environmentally friendly. Furthermore, the advantages of natural fillers over traditional fillers are acceptable specific strength and modulus, lightweight, and good biodegradability, which is very desirable nowadays. Therefore, the development and progress of "green products" based on epoxy resin and natural fillers as reinforcements have been increasing. Many uses of natural plant-derived fillers include many plant wastes, such as banana bark, coconut shell, and waste peanut shell, can be found in the literature. Partially biodegradable polymers obtained by using natural fillers and epoxy polymers can successfully reduce the undesirable epoxy and synthetic fiber waste. Additionally, partially biopolymers based on epoxy resins, which will be presented in the paper, are more useful than commercial polymers due to the low cost and improved good thermomechanical properties.

9.
Sci Rep ; 12(1): 397, 2022 01 10.
Artigo em Inglês | MEDLINE | ID: mdl-35013525

RESUMO

In this work, fillers of waste chicken feather and abundantly available lignocellulose Ceiba Pentandra bark fibers were used as reinforcement with Biopoxy matrix to produce the sustainable composites. The aim of this work was to evaluate the mechanical, thermal, dimensional stability, and morphological performance of waste chicken feather fiber/Ceiba Pentandra bark fiber filler as potential reinforcement in carbon fabric-layered bioepoxy hybrid composites intended for engineering applications. These composites were prepared by a simple, low cost and user-friendly fabrication methods. The mechanical (tensile, flexural, impact, hardness), dimensional stability, thermal stability, and morphological properties of composites were characterized. The Ceiba Pentandra bark fiber filler-reinforced carbon fabric-layered bioepoxy hybrid composites display better mechanical performance compared to chicken feather fiber/Ceiba Pentandra bark fiber reinforced carbon fabrics layered bioepoxy hybrid composites. The Scanning electron micrographs indicated that the composites exhibited good adhesion at the interface of the reinforcement material and matrix system. The thermogravimetric studies revealed that the composites possess multiple degradation steps, however, they are stable up to 300 °C. The thermos-mechanical studies showed good dimensional stability of the composites. Both studied composites display better thermal and mechanical performance compared to neat bioepoxy or non-bioepoxy thermosets and are suitable for semi-structural applications.

10.
Int J Biol Macromol ; 191: 572-583, 2021 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-34582904

RESUMO

Green thermoplastic starch (TPS) nanocomposite films aided by cellulose nanofibers (CNFs) from Chrysopogon zizanioides roots were developed and characterized. When compared to other lignocellulosic fibers, Chrysopogon zizanioides roots revealed exceptionally high cellulose content (~48%). CNFs were separated using an environmentally friendly acid isolation technique that included three stages: (i) alkali treatment; (ii) bleaching; and (iii) mild acid hydrolysis using oxalic acid in an autoclave. Following that, green nanocomposite films were made from potato starch using the solution casting process, by which we used glycerol (30 wt%) to make thermoplastic starch. Then, cellulose nanofibers in different concentrations (0, 1, 2, 3, 4 wt%) were added to the thermoplastic starch matrix. The isolated CNFs had diameters in the range of 17-27 nm. Besides, these nanostructures presented a very high crystallinity index (~65%), thereby enhanced the thermal stability. TPS/CNF green nanocomposites containing 3 wt% CNFs had exceptional tensile strength (~161%), tensile modulus (~167%), thermal stability, and crystallinity. As a result, nanocomposite films made of starch and cellulose nanofibers (3 wt%) extracted from Chrysopogon zizanioides roots would be alternatives for sustainable packaging. It can be concluded that Chrysopogon zizanioides roots have high potential for polymer industry.


Assuntos
Celulose/análogos & derivados , Vetiveria/química , Nanocompostos/química , Nanofibras/química , Amido/análogos & derivados , Filmes Comestíveis , Hidrólise , Resistência à Tração
11.
J Environ Health Sci Eng ; 18(2): 1311-1327, 2020 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-33312644

RESUMO

Here the fabrication of a novel PVA/CMC/halloysite nanoclay membrane for the effective adsorption of cationic dye (methylene blue, MB) from aqueous environment is reported. The membranes were analyzed through scanning electron microscopy (SEM), optical microscopy (OM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), contact angle and universal testing machine (UTM) analysis. The adsorption behavior of the membrane in terms of nanoclay loading, contact time, initial concentration of MB, pH and temperature were also discussed. The membrane exhibits excellent removal efficiency (99.5%) for MB in the optimal conditions such as nanoclay dose = 6 wt%, initial dye concentration = 10 ppm, contact time = 240 min, pH = 10 and temperature = 30 °C. Three isotherm models (Freundlich, Langmuir and Temkin) were employed to analyze the dye adsorption data. The results revealed that the adsorption process could be described well with both Freundlich and Langmuir isotherm model. The kinetics of MB adsorption onto membrane follows pseudo-second-order model while thermodynamic parameter indicate that adsorption is feasible and endothermic in nature. The antibacterial studies revealed that the PVA/CMC/halloysite nanoclay membrane possess notable antibacterial property. Finally, the desorption studies showed that the membrane have good reusability even after four recycles.

12.
Polymers (Basel) ; 12(10)2020 Sep 30.
Artigo em Inglês | MEDLINE | ID: mdl-33008025

RESUMO

Epoxy-based biocomposites are a good alternative for metals in lightweight applications. This research has been focused on the effect of accelerated weathering on the mechanical, thermal, contact angle, and water absorption behavior of neat epoxy, individual kenaf and sisal, and kenaf/sisal hybrid epoxy composites. The composite was fabricated by hand layup method. Among the various composites studied, sisal/kenaf/sisal hybrid epoxy composites showed the best properties and retained the thermo-mechanical properties with the lowest water absorption properties even after the weathering test. Thus, composites with hybridized kenaf and sisal with sisal outer layer are encouraging semistructural materials in outdoor applications.

13.
Sci Rep ; 10(1): 15452, 2020 09 22.
Artigo em Inglês | MEDLINE | ID: mdl-32963327

RESUMO

In this study, a novel PVA/SA/ZSM-5 zeolite membrane with good regeneration capacity was successfully prepared by solvent casting technique. The properties of the membranes were assessed by employing different characterization techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), optical microscopy (OP), thermogravimetric analysis (TGA), contact angle and universal testing machine (UTM). XRD, TGA and UTM results revealed that the crystallinity and thermo-mechanical performance of the membrane could be tuned with zeolite content. The successful incorporation of zeolite into the polymer matrix was confirmed by FT-IR, SEM and OP analysis. The adsorption ability of the as-prepared membrane was evaluated with a model anionic dye, Congo red. Adsorption studies show that the removal efficiency of the membrane could be tuned by varying zeolite content, initial concentration of dye, contact time, pH and temperature. Maximum dye adsorption (5.33 mg/g) was observed for 2.5 wt% zeolite loaded membrane, at an initial dye concentration of 10 ppm, pH 3 and temperature 30 °C. The antibacterial efficiency of the membrane against gram-positive (Staphylococcus aureus) and gram-negative bacteria (Escherichia coli) was also reported. The results show that membrane inhibits the growth of both gram-positive and gram-negative bacteria. The adsorption isotherm was studied using two models: Langmuir and Freundlich isotherm. The results show that the experimental data fitted well with Freundlich isotherm with a high correlation coefficient (R2 = 0.998). Meanwhile, the kinetic studies demonstrate that pseudo-second-order (R2 = 0.999) model describe the adsorption of Congo red onto PVA/SA/ZSM-5 zeolite membrane better than pseudo-first-order (R2 = 0.972) and intra particle diffusion model (R2 = 0.91). The experimental studies thus suggest that PVA/SA/ZSM-5 zeolite could be a promising candidate for the removal of Congo red from aqueous solution.

14.
Soft Matter ; 16(14): 3363-3377, 2020 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-32215406

RESUMO

The viscoelastic effects during reaction induced phase separation play an important role in toughening epoxy-based blends. The large difference in molecular weight/glass transition temperature between the blend components before the curing reaction results in dynamic asymmetry, causing viscoelastic effects during phase separation accompanying the curing reaction. This review will focus on the key factors responsible for viscoelastic phase separation in epoxy-based blends and hybrid nanocomposites. Time-resolved characterization techniques such as rheometry, small angle laser light scattering, optical microscopy etc., are mainly used for monitoring the viscoelastic effects during phase separation. Incorporation of nanofillers in epoxy thermoplastic blends enhances the viscoelastic phase separation due to the increase in dynamic asymmetry. Different theoretical models are identified for the determination of processing parameters such as temperature, viscosity, phase domain size, and other parameters during the viscoelastic phase separation process. The effect of viscoelastic phase separation has a very strong influence on the domain parameters of the blends and thereby on the ultimate properties and applications.

15.
Int J Biol Macromol ; 154: 329-338, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32179114

RESUMO

In a world that canopies numerous opportunities to advance towards a green sustainable life, biopolymer development offers a platform that fits into the paradigm of achieving an eco-friendly environment whilst reducing reliance on the scarce fossil fuel elements for the fabrication of day-to-day products. Today's technological improvements have aided biopolymer end-products to escalate to higher purposes and soon may have their performance level in par with the petroleum-based synthetic polymers. The motive of this paper is to shimmer light on some aspects of biopolymers that include its classes, properties, composites and applications. Depending on the type of class on the basis of various categories, many enthralling chemistries of polymer composition can be substantiated. Essential properties can imparted to the ensuing biopolymer by altering its chemical configuration and method of synthesis while also focusing on its functional purpose. Nowadays, biopolymer composites blend qualities of one biopolymer with another to acquire an enhanced component that showcases unique explicit attributes. There are several techniques to process biopolymer composites, of which in-situ, infiltration and electrospinning methods have captured considerable limelight. Biopolymers and its composites have embarked captivating impressions in regions of biomedical, packaging, agricultural and automotive applications. Although their efficacy is yet to reach their fossil fuel counterparts, biopolymers have laid a distinguishing mark that will continue to inspire creation of novel substances for many years to come.


Assuntos
Biopolímeros/química , Fenômenos Químicos , Nanocompostos/química , Embalagem de Produtos
16.
Waste Manag ; 97: 71-81, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31447029

RESUMO

The effect of recycling on the thermo-mechanical and water absorption behavior of polypropylene (PP)/sisal fiber and polylactic acid (PLA)/sisal fiber composites were studied. The PP-based non-biodegradable composites and PLA-based biodegradable composites were recycled for four times. The effect of recycling was determined by examining the morphology, thermo-mechanical properties, and water absorption behavior and the obtained results were compared. The results showed that the incorporation of sisal fibers in the PP and PLA matrix enhances the tensile modulus and percentage crystallinity of the composites. The tensile strength and modulus of the sisal fiber reinforced PP composites were not affected with recycling. Even though the tensile properties of PLA and PLA/sisal fiber reinforced composites are superior to PP and PP/sisal fiber composites, the PLA-based composites show a dramatic decrease in tensile strength and modulus after the first recycling due to the degradation of the polymer. The thermal stability of the PP/sisal fiber composites was not affected by the repeated recycling process. On the other hand, the PLA-based composites with higher sisal fiber content show a bit lower thermal stability after recycling. The PP-based composites show fluctuations in percentage crystallinity with recycling. On the other hand, a remarkable increase in percentage crystallinity for PLA and PLA-based composites was observed with increasing recycling times. Water diffusion study divulges that the diffusion of water into the polymer composites was reduced with recycling, irrespective of the polymer matrix.


Assuntos
Polipropilenos , Água , Poliésteres , Reciclagem
17.
Carbohydr Polym ; 207: 108-121, 2019 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-30599990

RESUMO

Designing environmentally friendly materials from natural resources represents a great challenge in the last decade. However, the lack of fundamental knowledge in the processing of the raw materials to fabricate the composites structure is still a major challenge for potential applications. Natural fibers extracted from plants are receiving more attention from researchers, scientists and academics due to their use in polymer composites and also their environmentally friendly nature and sustainability. The natural fiber features depend on the preparation and processing of the fibers. Natural plant fibers are extracted either by mechanical retting, dew retting and/or water retting processes. The natural fibers characteristics could be improved by suitable chemicals and surface treatments. This survey proposes a detailed review of the different types of retting processes, chemical and surface treatments and characterization techniques for natural fibers. We summarize major findings from the literature and the treatment effects on the properties of the natural fibers are being highlighted.

18.
Int J Biol Macromol ; 125: 99-108, 2019 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-30528990

RESUMO

The aim of this study is to investigate natural cellulosic fibers extracted from Tridax procumbens plants. The obtained fibers were alkali treated for their effective usage as reinforcement in composites. The physical, chemical, crystallinity, thermal, wettability and surface characteristics were analyzed for raw, and alkali treated Tridax procumbens fibers (TPFs). The test results conclude that there was an increase in cellulose content with a reduction in hemicellulose, lignin, and wax upon alkali treatment. This enhanced the thermal stability, tensile strength, crystallinity, and surface roughness characteristics. The contact angle was also lesser for treated TPFs which prove its better wettability with the liquid phase. The Weibull distribution analysis was adopted for the analysis of the fiber diameter and tensile properties. Thus the considerable improvement in the properties of alkali treated TPFs would be worth for developing high-performance polymer composites.


Assuntos
Álcalis/química , Asteraceae/química , Celulose/química , Fenômenos Químicos , Extração Líquido-Líquido , Análise Espectral , Resistência à Tração , Termogravimetria
19.
Sci Rep ; 8(1): 2803, 2018 02 12.
Artigo em Inglês | MEDLINE | ID: mdl-29434231

RESUMO

Graphene based room temperature flexible nanocomposites were prepared using epoxy thermosets for the first time. Flexible behavior was induced into the epoxy thermosets by introducing charge transfer complexes between functional groups within cross linked epoxy and room temperature ionic liquid ions. The graphene nanoplatelets were found to be highly dispersed in the epoxy matrix due to ionic liquid cation-π interactions. It was observed that incorporation of small amounts of graphene into the epoxy matrix significantly enhanced the mechanical properties of the epoxy. In particular, a 0.6 wt% addition increased the tensile strength and Young's modulus by 125% and 21% respectively. The electrical resistance of nanocomposites was found to be increased with graphene loading indicating the level of self-organization between the ILs and the graphene sheets in the matrix of the composite. The graphene nanocomposites were flexible and behave like ductile thermoplastics at room temperature. This study demonstrates the use of ionic liquid as a compatible agent to induce flexibility in inherently brittle thermoset materials and improve the dispersion of graphene to create high performance nanocomposite materials.

20.
Phys Chem Chem Phys ; 17(19): 12760-70, 2015 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-25902727

RESUMO

Styrene-block-butadiene-block-styrene (SBS) copolymers epoxidised at different epoxidation degrees were used as modifiers for diglycidyl ether of the bisphenol A-diamino diphenyl methane (DGEBA-DDM) system. Epoxy systems containing modified epoxidised styrene-block-butadiene-block-styrene (eSBS) triblock copolymer with compositions ranging from 0 to 30 wt% were prepared and the curing reaction was monitored in situ using rheometry and pressure-volume-temperature (PVT) analysis. By controlling the mole percent of epoxidation, we could generate vesicles, worm-like micelles and core-shell nanodomains. At the highest mole percent of epoxidation, the fraction of the epoxy miscible component in the triblock copolymer (epoxidised polybutadiene (PB)) was maximum. This gave rise to core-shell nanodomains having a size of 10-15 nm, in which the incompatible polystyrene (PS) becomes the core, the unepoxidised PB becomes the shell and the epoxidised PB interpenetrates with the epoxy phase. On the other hand, the low level of epoxidation gave rise to bigger domains having a size of ∼1 µm and the intermediate epoxidation level resulted in a worm-like structure. This investigation specifically focused on the importance of cure rheology on nanostructure formation, using rheometry. The reaction induced phase separation of the PS phase in the epoxy matrix was carefully explored through rheological measurements. PVT measurements during curing were carried out to understand the volume shrinkage of the blend, confirming that shrinkage behaviour is related to the block copolymer phase separation process during curing. The volume shrinkage was found to be maximum in the case of blends with unmodified SBS, where a heterogeneous morphology was observed, while a decrease in the shrinkage was evidenced in the case of SBS epoxidation. It could be explained by two effects: (1) solubility of the epoxidised block copolymer in the DGEBA leads to the formation of nanoscopic domains upon reaction induced phase separation and (2) the plasticisation effect of the epoxidised block copolymer in the epoxy resin.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA