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Poly(lactic acid)-starch/Expandable Graphite (PLA-starch/EG) Flame Retardant Composites
Get PDFThis work reports on the effect of commercial expandable graphite (EG) on the flammability and thermal decomposition properties of PLA-starch blend. The PLA-starch/EG composites were prepared by melt-mixing and their thermal stability, volatile pyrolysis products and flammability characteristics were investigated. The char residues of the composites, after combustion in a cone calorimeter, were analyzed with environmental scanning electron microscopy (ESEM). The thermal decomposition stability of the composites improved in the presence of EG. However, the char content was less than expected as per the combination of the wt% EG added into PLA-starch and the % residue of PLA-starch. The flammability performance of the PLA-starch/EG composites improved, especially at 15 wt% EG content, due to a thick and strong worm-like char structure. The peak heat release rate (PHRR) improved by 74%, the total smoke production (TSP) by 40% and the specific extinction area (SEA) by 55%. The improvements are attributed to the ability of EG to exfoliate at increased temperatures during which time three effects occurred: i) cooling due to an endothermic exfoliation process, ii) dilution due to release of H2O, SO2 and CO2 gases, and iii) formation of a protective intumescent char layer. However, the CO and CO2yields were found to be unfavorably high due to the presence of EG
Biogenic Amorphous Silica as Filler for Elastomers
Get PDFNatural products from agricultural wastes are finding importance in the polymer industry due to their many advantages such as being lightweight, low cost and environmentally friendly. In the present study the potential of the two types of rice husk ash (RHA) prepared under different conditions as fillers in natural rubber-based elastomer composites was investigated. The fillers were prepared by rice husks incineration and characterized by means of X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET) specific surface area, Hg-porosimetry and N2-adsorption. The evaluation involved determining the vulcanization characteristics of the compounds and their physical and mechanical characteristics, resistance to thermal aging as well as the dynamic properties of the vulcanizates containing RHA. It has been found that the ash from rice husk has good potential as filler in elastomers, especially as a substitute for synthetic commercially available silica. RHA improves the grip on ice and snow better than standard silica and may be used in formulations for shoe soles used for winter sports, extreme hiking footwear, ski boot soles, winter tire protectors, etc. Its quality depends on the conditions under which rice husk is incinerated. It is recommended to run the process at a temperature not higher than 800 °C. In particular, cases in which the vulcanizates contain biogenic silica have very interesting characteristics like improved modulus at 300% of elongation, lower residual elongation, higher mechanical loss angle tangent at 0 °C and lower at 60 °C, and are superior to those of the vulcanizates containing commercially available filler Ultrasil® 7000 GR
Super Absorption Behavior of Chitosan by Freeze-Blasting in Different Alkaline Solvents
Get PDFThe absorption behavior of chitosan in alkaline solution by freeze-blasting was studied. The influence of alkaline type, concentration, and small molecules was investigated, as well as the different roles of LiOH and NaOH in the absorption. Chitosan reached its maximum absorption rate when LiOH concentration was 4.8 wt% and NaOH 4.0 wt%, respectively. Chitosan showed better absorption capacity in LiOH solution. Urea could improve the absorption when its concentration was more than or equal to 4.0 wt%, and the improvement was greater in NaOH solution. Thiourea showed no obvious effect in LiOH solution, but showed an effect when NaOH concentration was 4.0 wt% and 6.0 wt%. During the absorption, NaOH only reacted with -OH of chitosan, while LiOH not only reacted with -OH of chitosan, but also reacted with the acetyl group of chitosan. LiOH was more powerful in destroying hydrogen bonding of chitosan. LiOH/urea solution may be a uniquely powerful solvent for chitosan
Mechanical and Thermal Properties of Sugar Palm Fiber Reinforced Thermoplastic Polyurethane Composites: Effect of Silane Treatment and Fiber Loading
Get PDFThe aim of the present study was to develop sugar palm fiber (SPF) reinforced thermoplastic polyurethane (TPU) composites and to investigate the effects of fiber surface modification by 2% silane treatment and fiber loading (0, 10, 20, 30, 40 and 50 wt%) on the mechanical and thermal properties of the obtained composites. Surface treatment was employed to improve the fiber-matrix interface, which was expected to boost the mechanical strength of the composites, in terms of tensile, flexural and impact properties. Thermal properties were also investigated by thermal gravimetric analysis (TGA) and dynamic mechanical analysis (DMA) to assess the thermal stability of the developed composites. Furthermore, scanning electron microscopy (SEM) was used to study the tensile fracture samples of composites with a view towards evaluating the effects of fiber surface treatments on the fiber/matrix interfacial bonding. The findings of this study reveal that the silane treatment has determined good bonding and linkage of the cellulose fiber to the TPU matrix, hence contributing to enhanced mechanical and thermal properties of the composites. The composite formulation with 40 wt% sugar palm fiber loading showed optimum values such as 17.22 MPa for tensile, 13.96 MPa for flexural, and 15.47 kJ/m2 for impact strength. Moreover, the formulations with higher fiber content exhibited satisfactory values of storage modulus and thermal degradation, while their good interfacial adhesion was evidenced by SEM images
Reinforcement of Thermoplastic Starch Films with Cellulose Fibres Obtained from Rice and Coffee Husks
No full textCellulosic fibres from coffee (CF) and rice (RF) husks have been obtained applying chemical treatments and characterized as to their microstructure and thermal behaviour. These materials have been incorporated into glycerol plasticised thermoplastic starch (TPS) films obtained by melt blending and compression moulding at 1 wt%, 5 wt% and 10 wt%. Microstructure, thermal behaviour and optical, tensile and barrier properties of the composites were analysed. Both kinds of micro-fibres improve the film stiffness while reduced the film stretchability. However, CF better maintained the film ductility at 1 and 5 wt%. A network of fine oriented fibres was observed on the surface of the films, while internal fibres exhibited a good adherence to the polymer network. The water vapour permeability of TPS films was not reduced in composites, although oxygen permeability was lowered by about 17%. Film transparency decreased by fibre addition in the UV-VIS range. Thermal stability of composites was slightly higher than net TPS films
Viscoelastic and Thermal Properties of Polyurethane Foams Obtained from Renewable and Recyclable Components
No full textThis article deals with the study of the viscoelastic and thermal properties of polyurethane (PU) rigid foams from biobased and recycled components. Rapeseed oil (RO) and recycled poly(ethylene terephthalate) (PET) were used to synthesize PU polyols. Addition of adipic acid (ADA) to polyol resulted in improved thermal and viscoelastic properties of foam materials. ADA content was varied from 1 to 6 wt%. Results of the dynamic mechanical spectra indicate an increase of the storage modulus E′ and the loss modulus E″ in the whole temperature range for specimens with higher loading of ADA. In addition, damping factor shifted to higher temperatures, but damping intensity remained almost unaffected by the compositions. Scanning electron microscopy of the foams’ cross sections testified that the average cells’ size of 110 mm was unaffected by the ADA content in polyol
Novel Approaches of Using of Spirulina Platensis in Natural Rubber Based Composites
No full textThe aim of this work was to investigate the influence of Spirulina (Spirulina platensis) as a natural filler on the curing characterization, morphology and mechanical, thermomechanical and thermal properties of natural rubber (NR) based composites. Spirulina was introduced into NR mixture in amount of 0 phr, 10 phr and 30 phr. The vulcanization process was carried out at the determined process condition by using hydraulic press at optimum vulcanization time (t90). It was noticed that Spirulina affected on the reduction of t90, and scorch time (t2) of the NR mixtures. Obtained vulcanizates were subjected to the number of tests e.g. scanning electron microscopy analysis, mechanical dynamical analysis, tensile test, hardness, and thermogravimetry. Generally, it was found that Spirulina added in amount of 10 phr NR positively influenced on tensile strength (TSb), storage modulus and hardness of obtained composites
Properties of Natural Rubber Biocomposities Filled with Alkaline Modified Oat Straw
No full textNovel elastomer biocomposites based on straw fibers (raw or chemically modified) as reinforcing elements of natural rubber (NR) were reported and studied. Oat straw fibres with different average lengths were used. Lignocellulose materials were incorporated into the elastomer, before and after chemical surface modification involving sodium hydroxide. Fourier transform infrared spectroscopy (FTIR) and microscopy techniques were employed for characterization of fillers. The kinetics of rubber mixtures, as well as rheometric properties of compounds were determined. The cross-linking density was executed on the basis of equilibrium solvent-swelling measurements applying the modified Flory–Rehner equation. The morphology of biocomposites samples was analyzed by a scanning electron microscopy. Mechanical characteristic: the values of hardness, tensile strength and attenuation coefficient were also determined. The physical and chemical investigations have proved the reinforcing effect of treated oat straw on natural rubber vulcanizates
Primary and Secondary Flows on Unsteady MHD Free Convective Micropolar Fluid Flow Past an Inclined Plate in a Rotating System: a Finite Element Analysis
Get PDFIn the present paper, a numerical analysis is performed to study the primary and secondary flows of a micropolar fluid flow past an inclined plate with viscous dissipation and thermal radiation in a rotating frame. A uniform magnetic field of strength Bo is applied normal to the plane of the plate. The whole system rotates with uniform angular velocity about an axis normal to the plate. The governing partial differential equations are transformed into coupled nonlinear partial differential equations by using the appropriate dimensionless quantities. The resulting equations are then solved by the Galerkin finite element method. The influencing pertinent parameters like primary and secondary velocities, primary and secondary angular velocities, temperature and concentration profiles are represented with the help of graphs. The validity and accuracy of finite element code is benchmarked with the results reported in the literature under some limiting cases. The study is relevant to rotating MHD (magnetohydrodynamics) energy generators utilizing non-Newtonian working fluids and magnetic rheo-dynamic materials processing systems
Effect of Geometrical Parameters on Vortex Fluidic Oscillators Operating with Gases and Liquids
Get PDFThe fluidic oscillator is an interesting device developed for passive flow measurement. These microsystems can produce a high oscillating jet frequency with high flow velocity. The main advantages of fluidic oscillators are that no moving parts is included in the device. Commercial CFD code FLUENT was used to perform analysis of flows in fluidic oscillator. Numerical simulations were carried out for different flow conditions, where water and air were used as working fluids. The oscillation frequencies were identified by the discrete fast Fourier transform method (FFT). Furthermore a low-pressure vortex of fluid flow in the oscillating chamber was observed. The effect of the operating pressure and the oscillating chamber shape on the fluidic oscillator performance is investigated. Moreover the velocity fluctuations of the feedback flows through both feedback channels and the output were determined quantitatively. In addition, the behaviour of the low-pressure vortex in both models is analysed. Also, numerical result revealed small vortices are developed at the end of nozzle while oscillation, which maintains the deflection of jet flow between attachments wall. Comparison of our numerical simulations with available results showed reasonably and good agreement