Evaluation of the hybridization effect on the thermal and thermo-oxidative stability of bamboo/kenaf/epoxy hybrid composites

Bamboo-/kenaf-reinforced epoxy hybrid composites were prepared by hand layup method. The aim of this study is to look into the hybridization effect of bamboo and kenaf fibers at different ratios on thermal and thermo-oxidative (TOD) stabilities of hybrid composites. Three types of hybrid composites were fabricated with different mass ratios of bamboo fiber mat (B) to kenaf fiber mat (K), namely B/K 70:30, B/K 50:50 and B/K 70:30 while maintaining total fiber loading of 40% by mass. The thermal stability and thermo-oxidative (TOD) stability were analyzed by thermogravimetric analyzer. Differential scanning calorimetry (DSC) was used to investigate the oxidation onset temperature (OOT) of all the composites. The results reveal that bamboo composite shows higher thermal stability than kenaf composite in both inert and oxidative atmospheres. An increase in bamboo fibers mass ratio in the hybrid composite improved the thermal and TOD stability. The thermal and TOD stabilities of the hybrid composites follow the sequence of B/K 70: 30?>?B/K 50:50?>?B/K 30:70. Pure epoxy composite recorded the highest OOT at 197.50 °C. The results show that the addition of natural fiber in the epoxy matrix has significantly reduced the OOT compared to the pure epoxy. Data obtained from this work will help us to fabricate a sustainable and biodegradable component for automotive or building materials.

     

Evaluation of the thermal stability of biodiesel blends of castor oil and passion fruit

The diversity of raw materials and technological routes employed in the biodiesel production has resulted in products with different chemical properties. This non-uniformity in the biodiesel composition may influence to the fuel quality. The aim of this study was to evaluate biodiesel blends of passion fruit and castor oil in different proportions and their thermal stability. Biodiesel blends of passion fruit and castor oil presented parameters in the standards of the Petroleum, Natural Gas and Biofuels National Agency. The TG curves indicated that castor oil biodiesel was more stable. Passion fruit biodiesel has a high content of oleic and linoleic acids, which are more susceptible to oxidation. Biodiesel blend of passion fruit and castor oil 1:1 increased the thermal stability in relation to passion fruit biodiesel. Biodiesel blend of passion fruit and castor oil 1:2 presented higher thermal stability, because castor oil has a high content of ricinoleic acid.     

Synthesis of polyolefin based materials with improved thermo-oxidative stability

Polyolefin based materials with chemically bonded phenol compounds have been synthesized. Two unsaturated polyolefins: an ethylene/propylene/5,7-dimethyl-1,6-octadiene terpolymer and an ethylene/5,7-dimethyl-1,6-octadiene copolymer, were used as starting materials. The functionalisation method involves a two-step procedure that consists in the hydrochlorination of the substituted pending double bonds, followed by grafting of the phenol compound. This procedure was found to be more effective for the terpolymer than for the corresponding copolymer. The reasons for this are discussed. A thermogravimetric study, in air atmosphere shows that, poly(ethylene-co-5,7-dimethyl-1,6-octadiene) grafted with 2-tert-butyl-4-methylphenol present improved thermo-oxidative stability when compared to a polyethylene reference.     

Influence of the storage on the thermo-oxidative stability of methyl and ethyl esters by PDSC

Biodiesel oxidation is a complex process widely influenced by the chemical composition of the biofuel and storage conditions. Several oxidation products can be formed from these processes, depending on type and amount of the unsaturated fatty acid esters. In this work, fatty acid methyl and ethyl esters were obtained by base-catalyzed transesterification of soybean oil and physicochemically characterized according to standards from ASTM, EN, and ABNT. The thermal and oxidative stabilities of biodiesel samples were investigated during the storage process by pressure differential scanning calorimetry (PDSC) and by viscosity measurements. Absolute viscosities of biodiesels after accelerated aging were also determined. The viscosity increased as the aging temperature and time were raised. The results showed that oxidation induction can occur during storage, decreasing the biodiesel stability. PDSC analysis showed that during storage under climate simulation the values of high-pressure oxidative induction times (HPOIT) were reduced for both FAEE and FAME.     

The effect of the hydration degree on the hydrothermal and thermo-oxidative stability of some collageneous matrices

The methods of the thermal analysis (TG, DTG and DTA) were used in order to investigate the effect of the hydration degree on the thermal behaviour of some collageneous matrices. It was pointed out that the degradation of hydrated collagen in the temperature range 20-400°C occurs through two successive processes accompanied by mass losses. The first process, consisting in the collagen dehydration, is endothermic and takes place in the temperature range ≈25 - ≈125°C. The second process is exothermic and consists in the decomposition and/or thermo-oxidation of dry collagen. The thermal parameters of both processes depend on the hydration degree of collagen. The observed dependencies show that the hydrothermal and thermo-oxidative stability of collagen are strongly correlated with its water content. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of natural antioxidants on the stability of polypropylene films

A preliminary study on the efficiency of agri-food industry wastes as stabilizers for polypropylene (PP) films is reported. Several analytical techniques were employed to evaluate the stabilization effectiveness of the additives. DSC and CL analysis performed on unaged samples confirmed the antioxidant activity of natural additives, and provided the following order of efficiency: red grape seeds > white grape seeds > tomato extracts. The films were also artificially aged at 70 °C, and FTIR spectroscopy confirmed the stabilization trend obtained from the unaged films. Kinetic analysis of TG data alongside tensile tests indicated that the tomato extract is a good thermal and processing stabilizer, but it is sensitive to oxidation. In contrast, grape seeds provide long-term stabilization to PP under conditions of oxidative degradation. Our results show that tomato and wine processing by-products have good potential to be exploited as a low-cost source of value-added phytochemicals.     

Characterization of thermo-oxidative stability of polymer optical fibers using chemiluminescence technique

The thermo-oxidative stability of commercially available polymer optical fibers (POFs) and their components (cores and claddings) was investigated. All the bare POFs (core and cladding only) studied here were based on poly(methyl methacrylate) (PMMA) core. The fibers were exposed to 100 °C/low humidity for about 4200 h. Chemiluminescence (CL) technique was applied to investigate the thermo-oxidative stability and for measuring the transmission loss during exposure a prototype device called multiplexer was used. POFs exhibited variation in thermo-oxidative stability although they possessed identical core material PMMA. This was due to difference in the chemical compositions of claddings. Claddings were more susceptible to the thermo-oxidative degradation compared to cores. The thermo-oxidative degradation of both the cladding and the core was found in POFs as a result of climatic exposure. POFs showed an early drop-off followed by a slow decline of transmission. The early drop-off of transmission was attributed to physical changes like thermal expansion and the slow decline of transmission to chemical changes like oxidative degradation of POFs. A good linear relationship between optical transmission stability and thermo-oxidative stability of POFs was established from these studies.     

Improvement of the thermo-oxidative stability of low-density polyethylene films by organic-inorganic hybrid coatings

LDPE films have been coated with single or bi-layer hybrid coatings formed through sol-gel reactions in order to improve their thermo-oxidative resistance. Different chemical compositions of the coating were investigated which differ either in the amount of the inorganic phase (silica deriving from tetraethoxysilane) or in the organic component (either alkoxy silane functionalized polyethylene-poly(ethylene glycol) diblock copolymers or poly(vinyl alcohol)). The thermo-oxidative stability of the coated films thus obtained has been assessed by means of isothermal differential scanning calorimetry (DSC) and isothermal thermo-gravimetric analysis (TGA) under accelerated conditions, i.e. at high temperatures in pure oxygen flow. Conventional ageing in air at lower temperature, slightly above the in-service one, has also been carried out. The obtained data show: a) a general improvement of the thermal-resistance for the coated LDPE samples; b) a particularly high thermal-resistance for LDPE coated with a bi-layer coating with pure silica in the top layer; c) the effectiveness of the accelerated techniques in qualitatively assessing the thermo-oxidative resistance of the coated polymeric systems.     

Melt processed polyethylene/fullerene nanocomposites with highly improved thermo-oxidative stability

The thermo-oxidative stability of melt processed polyethylene composites with the two fullerenes C₆₀ and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was studied with the aim of comparing the stabilization effect of both fullerenes on three different polyethylenes (PE). The results obtained show that, irrespective of the specific polyethylene being considered, C₆₀ loadings as low as 1.0 wt% cause a dramatic increase in the thermo-oxidative stability of the corresponding composites (up to 64.8 °C at T2% and 113.8 °C at T5%, TX% being the temperature corresponding to a mass loss of X wt%), in agreement with previous reports. Furthermore, and more importantly, this work shows for the first time that the thermo-oxidation stability effect caused by PCBM is even higher than that of C₆₀, the difference between both being particularly significant in the early stages of degradation, i.e. for mass losses ≤2 wt%. For example, polyethylene composites with 1.0 wt% PCBM show T2% values which are systematically higher than those of the corresponding composites with 1.0 wt% C₆₀, the difference between the T2% values of the two composites being 38.8 °C, 67.1 °C and 26.4 °C in the three different polyethylenes considered. Therefore, when compared with C₆₀, PCBM is particularly more effective at delaying the beginning of the thermo-oxidative degradation. According to our results, PCBM loadings as low as 1.0 wt% can increase the thermo-oxidative stability of polyethylene composites by more than 130 °C and these are, as far as we know, the highest thermo-oxidative stability results induced by nanoparticles ever reported in the literature for polyethylene.     

Comparative characterization of Jatropha,soybean and commercial biodiesel

Oil was extracted from seeds of Jatropha Curcas,in high yields(up to 40% by weight).The extracted Jatropha oil was converted in a laboratory reactor to biodiesel by transesterification.Analysis of Jatropha oil and Jatropha biodiesel by GC/MS and GC/SIMDIS showed that Jatropha oil could be readily converted to a biodiesel product through NaOH catalyzed transesterification.The resulting biodiesel has desirable properties such as high cetane number and low flash point,which are major improvements over the prop...     

An alternative method by pressurized DSC to evaluate biodiesel antioxidants efficiency

The purpose of this article is to present an alternative method developed using pressurized differential scanning calorimetry (P-DSC) to evaluate the oxidative behavior of biodiesel obtained from soybean oil, produced by ethylic route (BSET), with and without the addition of synthetic antioxidants, as well as to compare the results with those obtained by Rancimat Method, which were carried out according to the European Official Standard Method EN 14112. BSET samples were analyzed using four different types of synthetic antioxidants at concentrations varying between 250, 500, and 1000 mg kg⁻¹. The measurements done by P-DSC were performed using static air at 80 psi and isothermal conditions at 110 °C, the same operating temperature than the Rancimat method. The experimental results of the oxidative stability measured from both methods have shown good correlations, which depend on the antioxidant, showing a gradual improvement in the oxidative stability of BSET with increasing added concentration of antioxidants. Opposite result behavior occurred for the measurements done in the presence of one of the antioxidants, which was composed by a significant content of components volatile below 110 °C, which accelerate the induction of the biodiesel oxidation in P-DSC method, but apparently do not interfere in the electrical conductivity measurement method (Rancimat). The advantages of the developed method using P-DSC technique with respect to Rancimat method is that it allows one to use a smaller sample, increases sensitivity to antioxidant action, reduces the analysis time for the evaluation of the antioxidant efficiency and detects any occurring oxidative process, independently of the volatility of the formed products, which may form oxidated products that remain in the liquid phase and that are non detectable by Rancimat method.     

Influence of Catalyst Residues on Thermo-oxidative Aging and Thermal Stability of Poly（butene-1）

Isotactic poly（butene-1） （iPB） with spherical morphology was synthesized successfully with bulk precipitation polymerization without post-treatment of the products. The bulk precipitation polymerization process made it possible for iPB to be used as general plastic due to the acceptable decreased cost compared with the solution polymerization process. The influence of catalyst residues on the aging and thermal stability of iPB synthesized by bulk precipitation polymerization method was investigated by gel permeation chromatography, mechanical performance testing, thermogravimetric analysis and infrared spectroscopic analysis. Commercial iPB and the lab-made iPB with varied catalyst residue contents were studied. The results demonstrated that the catalyst residues played an important role in the aging process of the iPB. A possible mechanism of aging promotion by catalyst residues was proposed.     

Effect of acid-treated multi-walled carbon nanotubes on thermo-oxidative stability and degradation behavior of silicone rubber

The effect of acid-treated multi-walled carbon nanotubes (MWCNTs) on thermo-oxidative stability and degradation behavior of silicone rubber (SR) was evaluated. Raman microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric (TG) analysis were performed to characterize the surface states of MWCNTs samples. The results demonstrated that after acid treatment the nanodefects and surface oxygen-containing groups (mainly hydroxyl and carboxyl groups) were formed and the number of them was gradually increased by increasing the treatment time. Then these MWCNTs were embedded into SR matrix. Furthermore, the thermo-oxidative stability and degradation behavior of MWCNTs/SR composites were studied using thermogravimetric/infrared spectrometry (TG-IR). Thermo-oxidative stability test in air revealed that the degradation of SR, at relatively low temperature, was mainly due to the oxidation of Si-CH₃ side groups and the generation of free radicals. This behavior was hindered by the MWCNTs’ surface nanodefects and hydroxyl groups, as proved by TG-IR study which revealed that the amount of carbonyl compounds was reduced more than 60%, compared with that of neat SR. Therefore, acid treatment led a better thermo-oxidative stability of MWCNTs/SR. For 4hAT-MWCNTs/SR, with maximum hydroxyl groups on MWCNTs surface, the T_i (defined as the temperature for 5% mass loss) of it is increased by 34.8 °C compared to that of neat SR, and even increased by 18.5 °C compared with that of raw-MWCNTs/SR.     

Evaluation of the effect of Si/Mo and oil/alcohol ratios in the production of biodiesel from soybean oil

Mo-KIT-6 catalysts precursors obtained by direct hydrothermal synthesis using different Si/Mo molar ratios (10, 20, 30) were evaluated in the production of biodiesel from the transesterification of soybean oil with methanol. A 2² + 3PtCt factorial design was used to evaluate the influence of alcohol/oil and Si/Mo ratios on biodiesel yield. ANOVA statistical analysis showed that Si/Mo ratio was the most significant variable. The factorial design showed that the optimal conditions for maximizing the biodiesel yield are: using the 10_Mo-KIT-6 catalyst, and an alcohol/oil ratio of 20/1 at 150 °C for 3 h. However, using the 20_Mo-KIT-6 catalyst with an alcohol/oil ratio of 15/1 the biodiesel yield is close to the maximum, having the advantage of using a lower amount of methanol, which means that the separation of non-reacted alcohol will consume less energy.     

Measurement of thermo-oxidative stability of isotactic polypropylene by isothermal long-term differential thermal analysis

The thermo-oxidative stability of isotactic polypropylene with different antioxidant concentrations between 0% and 0·1% has been studied using isothermal long-term differential thermal analysis (ILDTA). In the temperature range from 90°C to 210°C the oxidation maximum times were measured up to 2000 h. The Arrhenius plot of the reaction maxima showed straight lines over the whole temperature range, which were not affected by the crystallite melting range. Thus, extrapolations from short-term experiments at elevated temperatures to long-term behaviour at lower temperatures are possible.Ageing tests in a circulating-air oven at 140°C showed that the loss of thermo-oxidative stability with increasing ageing time was nearly linear. So the state of thermo-oxidative deterioration of isotactic polypropylene can be estimated by measurement of residual life time in an ILDTA experiment.The end of the oven life of polypropylene coincided with the loss of mechanical properties which was confirmed by a long-term tensile test at 100°C and 120°C.     

Improvement of thermo-oxidative stability of electrically insulating polymeric materials by organic-inorganic hybrid coating

The thermo-oxidative stability of poly(ethylene terephthalate) (PET) and low-density polyethylene (LDPE) films, coated with organic-inorganic hybrid coatings of various compositions, has been investigated after accelerated ageing tests, in order to ascertain a possible beneficial effect of these coatings on the electrical performances of these insulating materials. The results have shown that the coating affects degradation mechanisms for both LDPE and PET.Thermo-oxidation is slow in LDPE, leading to significantly better insulating characteristics after ageing: a strong reduction of the embrittlement time was also observed.The strong increase of crystallinity upon ageing, observed for both coated and uncoated PET samples, probably dominates the effect of ageing on the electrical properties. As a consequence, only slight beneficial effects on PET electrical performances have been observed (both on conductivity and electrical strength). On the other hand, the coating has a strong effect on molecular weight changes leading to a significant increase of molecular weight for coated PET, while uncoated PET undergoes a significant decrease. This suggests that coated PET should present significantly better properties upon very long times of ageing.     

Effect of compatibilizer and Irganox MD 1024 on the thermo-oxidative stability of PP/PP-g-MA/OMMT nanocomposites

The thermo-oxidative stability of polymeric materials reinforced with mineral fillers, such as clays, may be lower than that of pristine polymers, due to the presence of metallic ions and compatibilizing agents. In this paper, an effort was made to understand the influence that a compatibilizing agent and a metal deactivator bonded to a primary stabilizer has on the thermal stability of polypropylene/polypropylene-grafted maleic anhydride/organic montmorillonite (PP/PP-g-MA/OMMT) nanocomposites. At the first stage of this work, the organically modified montmorillonite clay is chemically analyzed by Inductively Coupled Plasma Atomic Emission Spectrometry to quantify the metals present in the clay. TGA, DSC, OIT, and dynamic OIT were used to assess the degradation of the nanocomposites. The results showed that the use of compatibilizing agents has a positive effect on the stability of nanocomposites in the initial steps of degradation, but has a degradative effect at higher temperatures, as indicated by the decreasing T_max for compatibilized nanocomposites. In relation to Irganox MD 1024, an increase in all the parameters for assessing the stability of nanocomposites was observed; however, the most significant change was the delay in the temperature at which the occurrence of exothermal reactions begins. Use of this additive is responsible for delaying the beginning of the exothermic reaction until a higher temperature, as a function of its concentration, as well the differences between the beginning of volatile release and the exothermal reactions. Also was discussed the influence of Irganox MD1024 concentration on T_max, and the difference of temperature between the beginning of heat releasing and the initial weight loss, which decreases as the stabilizer concentration is increased. Thanks to the association of dynamic OIT and TGA results from experiments performed with identical conditions. This complementary use of these techniques is a powerful tool for assessing the stability in the polymeric system.     

Ester-additives as inhibitors of the gelification of soybean oil methyl esters in biodiesel

Biodiesel from soybean oil transesterified with methanol (TSO) becomes viscous and gelifies at low storage temperatures which makes it difficult to pump. To inhibit this behaviour bulky esters were added to reduce the crystallization temperature of TSO and to modify the rate of conversion of crystallized mass. This rate was found to follow a JMAK kinetic model. The Avrami’s parameter n was constant for TSO, while two n values were found for TSO-additive solutions, meaning that the additives first slowed down the rate of nucleation and, later on as enough nuclei had been formed, crystal growth rate dominated and the previous crystallization rate was recovered.     

A novel method for the synthesis of biodiesel from soybean oil and urea

The increasing demand for energy has encouraged the development of renewable resources and environmentally benign fuel such as biodiesel. In this study, ethyl fatty esters (EFEs), a major component of biodiesel fuel, were synthesized from soybean oil using sodium ethoxide as a catalyst. By-products were glycerol and difatty acyl urea (DFAU), which has biological characteristics, as antibiotics and antifungal medications. Both EFEs and DFAU have been characterized using Fourier transform infrared (FTIR) spectroscopy, and ¹H nuclear magnetic resonance (NMR) technique. The optimum conditions were studied as a function of reaction time, reactant molar ratios, catalyst percentage and the effect of organic solvents. The conversion ratio of soybean oil into pure EFEs was 76% after 10 h of reaction. The highest conversion yield of EFEs is obtained when the urea/soybean oil ratio was from 6.2 mmol to 1 mmol, while the highest production of DFAU is obtained when the ethoxide (as a catalyst)/soybean oil ratio is from 6.4 mmol to 1 mmol in hexane as the reaction medium.