Characteristics of kenaf fibre/epoxy composites subjected to thermal degradation

Kenaf fibres are receiving much attention in the natural fibre composite industry due to its potential as polymer reinforcements. However, like all natural fibres, kenaf fibres have lower thermal resistance as compared to synthetic fibres. In this current work, the characteristics of kenaf fibre/epoxy composites, both treated and untreated using alkalization process, exposed to high temperature were studied. Thermogravimetric analysis (TGA) was used to study the thermal decomposition behaviour of treated and untreated kenaf/epoxy composites as well as their components, kenaf fibre and neat epoxy from room temperature up to 600 °C. The weight loss and physical changes of these samples were observed through furnace pyrolysis. Surface morphology of the composites after degradation was observed using scanning electron microscopy (SEM). The results from the TGA showed that the addition of kenaf fibres into the epoxy slightly improves both the charring and thermal stability of the samples. However, it was observed that alkalization causes reduction in these behaviours for the kenaf/epoxy composite. Generally, increased exposure time causes higher weight loss of the composites only up to 150 °C. At higher temperature, duration of exposure has little influence on the weight loss. Fibre-matrix debondings were observed on degraded samples implying mechanical degradation of the composites had occurred.     

Measurement of glass transition temperature by mechanical (DMTA), thermal (DSC and MDSC), water diffusion and density methods: A comparison study

Glass transition measured by DMTA from the change in slope in storage modulus was 55 °C, which was 10.5 °C lower than the value measured by tan δ peak. Initial glass transition measured by DSC, increased exponentially and reached a constant value of 55 °C at or higher heating rate of 30 °C/min. Transition temperature, measured by MDSC, remained constant up to heating rate 15 °C/min and then decreased. The glass transition values determined from reversible heat flow was 60 °C. The break in diffusivity and density (i.e. volume) was observed at 50 °C below the glass transition temperature measured by thermal and mechanical methods.     

Mechanical,Thermal and Morphological Behaviors of Castor Oil Based PU/PS Interpenetrating Polymer Network-Metakaolin Composites

The meta kaolin (MK) clay particulate filler with different weight ratios viz., 0, 5, 10, 20 and 30 wt% were incorporated into castable polyurethane (PU)/polystyrene (PS) (90/10) interpenetrating polymer network (IPN). The effects of MK particulate filler loading on the mechanical and thermal properties of PU/PS (90/10) IPN composites have been studied. From the tensile behavior, it was noticed that a significant improvement in tensile strength and tensile modulus as an increase in MK filler content. Thermogravimetric analysis (TGA) data reveals the marginal improvement in thermal stability after incorporation of MK filler. TGA studies of the IPN composites have been performed in order to establish the thermal stability and their mode of thermal degradation. It was found that degradation of all composites takes place in two steps. Degradation kinetic parameters were obtained for the composites using three mathematical models. Tensile fractured composite specimens were used to analyze the morphology of the composites by scanning electron microscopic (SEM) technique.     

Effect of molecular weight on thermal degradation mechanism of the biodegradable polyester poly(ethylene succinate)

A series of aliphatic polyesters, in particular poly(ethylene succinate), having different molecular weights, were synthesized from succinic acid and ethylene glycol, following the melt polycondensation process. Intrinsic viscosities (IV), GPC, DSC, ¹H NMR and carboxylic end group measurements were used for their characterisation. From thermogravimetric analysis, it was concluded that the molecular weight of polyesters achieved during polycondensation are strongly related to thermal stabilities of initial oligomers. In order to synthesise high molecular weight polyesters, the number average molecular weight of oligomers must not be lower than 2300–3000 g/mol, since thermal decomposition begins at temperatures lower than 200 °C. However, even in that case, polycondensation temperatures must not exceed 230–240 °C. From TGA studies, it was found that sample having different molecular weights could be divided into two groups characterized by different thermal stability. In the first group, belong samples with intrinsic viscosity of IV = 0.08 dL/g and in the second one all the other samples (IV > 15 dL/g). From kinetic analysis of thermal degradation, it was found that degradation of all polyesters takes place in three stages, its one corresponding to a different mechanisms. Degradation of samples with low molecular weight is more complex that that of polyesters having high molecular weights. The values of the activation energy and the exponent n for the two groups of samples—with different molecular weight—are similar, regarding the first two mechanisms, while there is an alteration in the case of the third mechanism.     

The effect of alumina surface activity on the properties of lignocellulose/pitch-Al2O3 composites

Lignocellulose–pitch-based composites carbonized at 1000 °C were easily prepared by blending lignocellulose with pretreated pitch in a proportion of 50:50 wt.%. The pretreatment of the pitch was carried out by thermal treatment at temperatures of 250 and 350 °C, both in the absence and in the presence of 10 wt.% of alumina of different surface activities (acid, neutral and basic). The structural and mechanical properties of the composites, evaluated by means of density/porosity determinations, optical microscopy and flexural strength, were found to be enhanced by the presence of alumina. The effects of the addition of alumina in the composite were evaluated by means of thermogravimetric analyses. The results indicate that alumina surface activity plays an important role in the interactions between the composite components. Neutral alumina has the greatest effect during the pretreatment, while acid alumina favors lignocellulose–pitch interactions during the processing of the composite. These effects are more pronounced when the pretreatment is performed at 350 °C. Lignocellulose–pitch-based composites with a water density of 1.75 g cm⁻³, a porosity of 30 vol.% and a flexural strength of 30 MPa can be obtained when the pitch is pretreated in the presence of neutral alumina.     

Thermal degradation of ethanolamine treated poly(vinyl chloride)/wood flour composites

The influence of ethanolamine treatment of wood flour on the thermal degradation behaviour of PVC/wood flour composites was investigated. The decomposition of untreated and treated wood flour and PVC/wood flour composites was measured using thermogravimetric analysis (TGA). The TGA indicated an accelerated degradation of the composite after treatment in a temperature range between 240 and 350 °C. This was caused by a synergistic decomposition of treated wood flour and polymer. Additionally, the colour of the material was measured in order to analyse the effect of the treatment. The lightness of the composite was reduced with increasing ethanolamine concentration.     

Thermal resistance and mechanical stability of tungsten oxide filled polymer composite radiation shields

Abstract

The influence of tungsten oxide on thermal and mechanical properties of Isophthalic polyester was studied in detail. Ultrasonication technique was successful in dispersing WO₃ filler particles upto 40?wt% into the polymer matrix and was confirmed through the Scanning Electron Microscopy technique. The mechanical strength of the composites was found to increase with increase in the WO3 content and is acting as a reinforcer. About 77.4%, 65.4% and 7–8 times increase was observed in tensile, flexural and compressive strength respectively with respect to pristine. The thermogram of the composites reveal two stages of degradation. Maximum weight loss was observed in the first stage of degradation in almost all the composites. The initial degradation temperature of the composites range from 151?°C–226?°C. Activation energy was estimated using Horowitz–Metzger kinetic theory and was found to range from 25.31 to 78.58?kJ/Mol. The 50?wt% WO3 filled composite exhibits excellent thermal stability and mechanical strength. Thus, WO₃ filler particles were successful in enhancing the thermal and mechanical strength of Isophthalic polyester.     

Thermal decomposition of zinc carbonate hydroxide

This study is devoted to the thermal decomposition of two zinc carbonate hydroxide samples up to 400 °C. Thermogravimetric analysis (TGA), boat experiments and differential scanning calorimetry (DSC) measurements were used to follow the decomposition reactions. The initial samples and the solid decomposition products were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and laser particle size analyzer. Results showed that zinc carbonate hydroxide decomposition started at about 150 °C and the rate of decomposition became significant at temperatures higher than 200 °C. The apparent activation energies (E_a) in the temperature range 150–240 °C for these two samples were 132 and 153 kJ/mol. The XRD analyses of the intermediately decomposed samples and the DSC results up to 400 °C suggested a single-step decomposition of zinc carbonate hydroxide to zinc oxide with not much change in their overall morphologies.     

Seawater ageing of flax/poly(lactic acid) biocomposites

Natural fibre reinforced biopolymer composites, or biocomposites, are an alternative to the glass fibre reinforced thermoset composites widely used today in marine applications. Biocomposites offer good mechanical properties and total biodegradability, but if they are to be adopted for marine structures their durability in a seawater environment must be demonstrated. In the present study unreinforced PLLA (Poly(l-Lactic acid)), injected and film stacked flax composites with the same PLLA matrix have been examined. All the samples were aged in natural seawater at different temperatures in order to accelerate hygrothermal ageing. Changes to physico-chemical and mechanical behaviour have been followed by weight measurements, thermal and gel permeation chromatography (GPC) analyses, and tensile testing, completed by acoustic emission recording and scanning electron microscopy (SEM) examination. The matrix tensile stiffness is hardly affected by seawater at temperatures to 40 °C but the composite loses stiffness and strength. Fibre/matrix interface weakening is the main damage mechanism induced by wet ageing, but both matrix and fibre cracks also appear at longer periods.     

Synergistic effect between expandable graphite and ammonium polyphosphate on flame retarded polylactide

Synergistic effect was observed between expandable graphite (EG) and ammonium polyphosphate (APP) on flame retarded polylactide (PLA) in this paper using limiting oxygen index (LOI), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and X-ray spectroscopy (XPS) and cone calorimeter tests etc. In the experiments, PLA composites with 15 wt% of APP/EG(1:3) combinations showed a LOI value of 36.5 and V-0 rating in UL-94 tests, greatly improved flame retardant properties from composites with APP or EG alone. Results from TGA and cone calorimeter demonstrated that APP/EG combination could retard the degradation of polymeric materials above the temperature of 520 °C by promoting the formation of a compact char layer. This char layer protects the matrix effectively from heat penetrating inside and prevents its further degradation, resulting in lower weight loss rate and better flame retarded performance.     

Synthesis, characterization and biodegradable studies of 1,3-propanediol based polyesters

A series of biodegradable polyesters were synthesized from dicarboxylic acids and 1,3-propanediol catalyzed by transestrification polycondensation reaction in the bulk. The structure, average molecular weights and physical properties of the resulting aliphatic polyesters were characterized by ¹H NMR, FT-IR, solution viscosity, GPC, DSC and TGA. Homopolyesters show higher degree of crystallinity, melting and thermal stability in comparison to copolyesters. The biodegradability of the polyesters was determined by monitoring the normalized weight loss of polyester films with time in phosphate buffer (pH 7.2) without and with Rhizopus delemar lipase at 37 °C. The rate of enzymatic degradation of homopolyesters follows the path PPSu > PPAd > PPSe. PPSe did not show significant weight loss in presence of enzyme which may be due to its highest degree of crystallinity and melting point compared to the PPSu, PPAd and copolyesters. In the soil burial degradation polyester sample showed severe surface degradation by the attack of microorganism.     

Nanosize and microsize clay effects on the kinetics of the thermal degradation of polylactides

Polylactide (PLA)-montmorillonite (MMT) micro- and nanocomposites based on semicrystalline and amorphous polymers and unmodified or organomodified clays at 5 wt% content were produced by melt mixing. Based on the three different test methods that were used to follow thermal degradation, different conclusions were obtained. During melt processing, thermomechanical degradation was more pronounced in the presence of all fillers, which apparently acted catalytically, but to different degrees. During isothermal degradation in air from 180 °C to 200 °C, degradation rate constants were calculated from novel equations incorporating changes in intrinsic viscosity (IV). Results show that the thermal degradation rate constants of the amorphous PLA and its composites are lower than those of the semicrystalline PLA and its composites. Due to better filler dispersion in the polymer matrix, the thermal degradation rate constants of the nanocomposites are significantly lower than those of the unfilled polymers and their microcomposites under air. As per dynamic TGA data and thermal kinetic analysis from weight losses and activation energy calculations, organomodified nanofillers have a complex effect on the polymer thermal stability; the unmodified fillers, however, reduce polymer thermal stability. These TGA data and kinetic analysis results also support the findings that the thermal stability of the amorphous PLA and its composites is higher than that of the semicrystalline polymer and its composites and the thermal stability of the nanocomposites is higher than that of the microcomposites. In general, mathematical modeling based on random thermal scission equations was satisfactory for fitting the TGA experimental data.     

Biodegradability of poly(butylene succinate) (PBS) composite reinforced with jute fibre

Poly(butylene succinate) (PBS)/jute composites were prepared, and the effects of fibre content, diameter, surface modification and arrangement forms on the biodegradability were evaluated by compost-soil burial test. The weight losses of PBS/jute composites are higher than that of pure PBS film and bulk jute fibre, and decreased with increasing fibre content. The weight loss of PBS/10% jute composite after 180 days is 62.5%. In the case of the effect of fibre diameter, the weight loss is found to decrease with decreasing fibre diameter. For the effect of fibre surface modification, the order of higher weight loss is PBS/untreated jute > PBS/alkali treated jute > PBS/coupling agent treated jute. Furthermore, the composite of PBS/woven fabric has the highest weigh loss, followed by that of PBS/nonwoven fabric and PBS/bulk jute fibre, respectively.     

Study of the thermal degradation of poly(furfuryl methacrylate) by thermogravimetry

The thermal degradation of poly(furfuryl methacrylate) (PFM) has been studied by means of dynamic thermogravimetric analysis (TGA) in the temperature range 100–600°C under nitrogen and oxygen atmospheres at various heating rates, and the apparent activation energy for the interval 230–340°C corresponding to the first degradation step was determined. Isothermal TGA at 250°C, 275°C and 300°C was carried out and the apparent activation energy values obtained were compared with those determined in dynamic experiments. The residues from isothermal degradation experiments were analysed by infrared spectroscopy and the results seem to indicate that in the thermal degradation of PFM the formation of cyclic structures of 2,4-dimethylglutaric anhydride occurs in the macromolecular chains, together with partial depolymerization of polymer segments, as well as intermolecular crosslinking through oxidation of the C---H bond in position 5 of some furfuryl rings.     

Surface molecular characterisation of different epoxy resin composites subjected to UV accelerated degradation using XPS and ToF-SIMS

Epoxy resin composites reinforced with E-glass (E), 3D glass (3D) and carbon fibre (CF) were subjected to an intense UV and high temperature accelerated degradation environment. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to provide a molecular characterisation of the surface of the degraded composites. The response at the surface of the epoxy resin composites to oxidative degradation is influenced by the composite reinforcement type and characteristics. XPS results indicate that 3D resin composites exhibit more surface oxidation as a result of the accelerated degradation in comparison with E and CF composites. Principal components analysis (PCA) of the ToF-SIMS positive ion spectra showed that E and 3D resin composites suffered chain scission while CF composites suffered chain scission and cross-linking reactions as a result of the intense UV exposure. The extent of the surface oxidation, cross-linking/condensation reaction and loss of low molecular weight (lower than C₄H_x) aliphatic hydrocarbons may be indicated using PCA of both the ToF-SIMS positive and negative ion spectra. PCA also provides insight for proposing epoxy resin chain scission and oxidation reaction mechanisms.     

Degradation of sisal fibre/Mater Bi-Y biocomposites buried in soil

Degradation of short sisal fibres/Mater Bi-Y™ biocomposites during indoor burial experiments was analysed. Within the first month, water sorption was the main event followed by weight loss. Water sorption results demonstrated that composites absorbed less water than the matrix. The lower sorption capacity of composites was related to the presence of fibre-fibre and fibre-matrix (both of carbohydrate nature) interactions which delay the water intake and enhances the material stability. In soil burial, all materials followed the same degradation pattern. The amorphous nature of the matrix favoured the preferential removal of starch, which was the most bio-susceptible material, as observed by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). Fibres seemed to play a secondary role in this process, as confirmed by the slight difference in weight loss between the matrix and composites (40 and 33 wt.%, respectively). The drop in mechanical properties as a function of the exposure time was associated with the preferential loss of matrix and fibre components and the detriment of the fibre/matrix interface.     

Studies of thermooxidative degradation process of chlorinated natural rubber from latex

The thermooxidative degradation of chlorinated natural rubber (CNR) from latex were studied by thermogravimetry (TG) coupled with Fourier Transform Infrared Spectroscopy (FTIR), ultraviolet-visible (UV-Vis) spectroscopy and difference FTIR. The CNR degraded in air atmosphere with two distinct steps of weight loss. The first step ranging from 160 to 390 °C, mainly is a dehydrochlorination reaction with a little oxidative scission of molecular backbones to release carbon dioxide and the conjugated polyene sequences (---[C=C]---)_n=3,4 are formed on the molecules of CNR. The second step ranging from 390 to 585 °C, is an oxidative degradation reaction of the molecular backbones of CNR and the evolved gas is only carbon dioxide.     

Pyrolysis of textile wastes: I. Kinetics and yields

Thermal behavior of textile waste was studied by thermogravimetry at different heating rates and also by semi-batch pyrolysis. It was shown that the onset temperature of mass loss is within 104–156 °C and the final reaction temperature is within 423–500 °C. The average mass loss is 89.5%. There are three DTG peaks located at the temperature ranges of 135–309, 276–394 and 374–500 °C, respectively. The first two might be associated with either with decomposition of the hemicellulose and cellulose or with different processes of cellulose decomposition. The third peak is possibly associated to a synthetic polymer. At a temperature of 460 °C, the expected amount of volatiles of this waste is within 85–89%. The kinetic parameters of the individual degradation processes were determined by using a parallel model. Their dependence on the heating rate was also established. The pyrolysis rate is considered as the sum of the three reaction rates. The pyrolysis in a batch reactor at 700 °C and nitrogen flow of 60 ml/min produces 72 wt.% of oil, 13.5 wt.% of gas and 12.5 wt.% of char. The kinetic parameters of the first peak do not vary with heating rate, while those of the second and the third peak increase and decrease, respectively, with an increasing heating rate, proving the existence of complex reaction mechanisms for both cases.     

Synthesis,Characterization, and Hydrolytic Degradation of Polylactide/Poly(ethylene glycol)/Nano-silica Composite Films

Poly(lactic acid) (PLA)/PEG/nano-silica composite degradable films have been prepared by solvent casting method. IR measurements showed that vibration of C–O–C group was confined by silica network. SEM results showed that nano-silica particles were dispersed uniformly in the PLA/PEG matrix. TGA results indicated that the thermal decomposition temperature rose with the increase of nano-silica content. The tensile strength of composite film increased by the addition of nano-silica particles into PLA/PEG matrix. The degradation rate of PLA/PEG/nano-silica composites increased with the acidic medium of degradation. On the other hand, the slower degradation was obtained in the neutral buffer solution. PLA/PEG/nano-silica composites were found to exhibit almost similar degradation behavior as that of PLA/PEG films.     

Simulation of the thermal degradation and curing kinetics of fly ash reinforced diglycidyl ether bisphenol A composite

Thermogravimetric Analysis (TGA) is concluding expanding applicability in determination of the thermal stability and degradation nature of materials. The present study investigates the thermal degradation behavior and the kinetics of degradation of epoxy mixed with varying percentages of 0, 2.5, 5, and 7.5 ​wt% fly ash. Thermal stability and degradation behavior of fly ash modified epoxy cast were determined by thermogravimetric analysis. The kinetic parameters of the EF composites were calculated by using Coats–Redfern, Broido and Horowitz–Metzger models under best-fit analysis and further proved by linear regression analysis. The kinetics of thermal degradation was calculated from data scanned at a heating rate of 10 ​°C/min. The obtained results reveal that kinetic parameters and thermal behavior of EF composites were improved with the reinforcement of fly ash. The cure kinetics of the varying content of fly ash reinforced epoxy cast were also studied by using a nonisothermal differential scanning calorimetric (DSC) technique at four different heating rates 5 ​°C/min, 10 ​°C/min, 15 ​°C/min and 20 ​°C/min. The curing kinetics of the EF composite was derived from the nonisothermal differential scanning calorimetry (DSC) data with the three Kissinger, Ozawa, and Flynn–Wall–Ozawa models, respectively.