Binary mixtures based on polycaprolactone and cellulose derivatives

Pyrolytic process has a promising potential for the environmentally friendly upgrading of lignocellulosic and plastic waste. Thermogravimetry and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) were used to get information about the reactive decomposition of PCL in binary mixtures with microcrystalline cellulose (MC) or sisal fibres (SF). Preliminary thermogravimetric investigation showed that biomass is thermally degraded at lower temperatures than PCL and this process has a predominant influence on the thermal behaviour of the mixtures. Discrepancies between the experimental and predicted TG/DTG profiles were considered as a measurement of the extent of interactions occurring on co-pyrolysis. It was found that reactivity of PCL was slightly increased in PCL-SF binary mixtures. Evolution of acidic products from cellulose and hemicelluloses decomposition may promote PCL degradation in binary mixtures with SF. It seems that the co-pyrolysis process could have potential for the environmentally friendly transformation of biocomposites.     

紫外光照射对皮胶原热降解活化能的影响

将皮胶原经不同时间的紫外光照射,采用热重法(TG)和微分热重分析(DTG)研究了照射前后皮胶原的热降解行为,用Horowitz-Metzger法和Coats-Redfern法计算了其热降解活化能,得到了未照射皮胶原和经过不同紫外线照射时间处理后的皮胶原的热降解活化能。研究发现,在较短时间(0~4h)的照射后,皮胶原的热降解活化能略有增大;在较长时间(8~64h)的照射后,皮胶原的热降解活化能大幅降低。这可能是由于在紫外光照射的过程中,皮胶原分子链发生了以交联为主和以断链为主的复杂光化学反应。     

Mechanical and thermal characterization of sisal fiber reinforced polylactic acid composites

The advantages of green composites are including, but not limited to their environmental friendly nature, lightweight, reduction of production energy and costs, and recyclability. This work focuses on the mechanical, thermal, and dynamic mechanical properties of biocomposites. For that purpose, biosourced polymers were used, namely polylactic acid (PLA) and sisal fiber, and biocomposites were extruded and then injection molded with different contents of sisal fibers (5%, 10%, 15%). The results show that the increase of the rate of reinforcement improves the mechanical and dynamic mechanical properties of the biocomposites made. By the increase of the sisal fiber content, the degree of crystallinity of the matrix was increased from 47% to 61%, as sisal fibers were acted as a nucleating agent for the PLA.     

氟橡胶/改性乙丙橡胶并用胶的热稳定性

采用热分析技术考察了氟橡胶及氟橡胶(FPM)/改性乙丙橡胶(MEPDM)并用胶在氮气中的热稳定性, 通过微分法与积分法两种动力学方法计算出了FPM及FPM/MEPDM并用胶的热分解活化能E和指前因子A. 结果表明, 并用胶的热分解温度稍高于纯的氟橡胶, 但热分解活化能略低于氟橡胶, FPM、FPM/MEPDM(5%)和FPM/MEPDM(10%)的热分解活化能分别为251.74、244.98和219.60 kJ·mol-1; 热分解反应级数n均为0.95. 随着失重百分率的增大, 热分解活化能增大.     

聚氨酯胶粘剂的热分解动力学研究

采用热分析技术考察了通用型聚氨酯胶粘剂在空气中的热解过程, 并通过TG方法和动力学方法研究了各步反应的活化能E、指前因子A等动力学参数. 通过等失重转化率法校验了两种方法所获得的E和A值. 结果表明, 聚氨酯胶粘剂有三个主要降解阶段, 第一降解阶段的活化能为144.31-148.35 kJ·mol^-1, 第二个降解阶段的活化能为196.96-204.26 kJ·mol^-1, 第三个降解阶段的活化能为202.97-205.27 kJ·mol^-1; 热降解过程为一级反应, 随着失重百分率的增大, 热分解反应活化能增大. 此外, 聚氨酯胶粘剂具有较高的热稳定性, 预测其在35 ℃的空气中失重5%时的热老化寿命为10年.     

New Regional Editor

Thermal decomposition of an agrowaste, namely banana trunk fibers (BTF) were investigated by thermogravimetry (TG) and derivative thermogravimetry (DTG) up to 900 °C at different heating rates (from 5 to 100 °C/min). The BTF was subjected to modification by means of various known chemical methods (mercerization, acetylation, peroxide treatment, esterification, and sulfuric acid treatment). Various degradation models, such as the Kissinger, Friedman, and Flynn–Wall–Ozawa were used to determine the apparent activation energy. The obtained apparent activation energy values (149–210 kJ/mol) allow in developing a simplified approach to understand the thermal decomposition behavior of natural fibers as a function of polymer composite processing.     

Impact of the nature and shape of cellulosic nanoparticles on the isothermal crystallization kinetics of poly(ε-caprolactone)

Polycaprolactone (PCL)/cellulose nanocomposites were prepared by mixing PCL with surface modified sisal nanowhiskers (CNW) and microfibrillated cellulose (MFC) extracted from sisal fibers. The influence of cellulosic nanoparticles on the crystallization behavior of PCL was investigated by differential scanning calorimetry. Isothermal crystallization data were modeled with Avrami’s kinetics, Lauritzen–Hoffman secondary nucleation theory and equilibrium melting points were determined with the Hoffman–Weeks method. The cellulose nanoparticles, acting as nucleating agents, drastically accelerate the crystallization of PCL while depressing its equilibrium melting by 9–10 °C. The crystallization of MFC-nanocomposites is slightly faster than that of CNW-nanocomposites, in agreement with the slightly lower bulk activation energy for crystallization and nucleation parameter in the former. The results are discussed based on the differences of specific surface area and surface chemistry of nanoparticles, as well as the confinement phenomenon.     

Correlation of the thermal stability and the decomposition kinetics of six different vegetal fibers

The thermal degradation behavior of six different vegetal fibers was studied using thermogravimetry under nitrogen atmosphere at four different heating rates (5, 10, 20 and 40 °C min^?1). The degradation models Kissinger, Friedman and Flynn–Wall–Ozawa methods were used to determine the apparent activation energy and the frequency factor of these fibers. Furthermore, the solid state degradation mechanisms were determined using Criado’s method. Additionally, X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy were analyzed to corroborate the obtained results. The results indicated that the apparent calculated activation energies can be more closely related to the exponential dependence of the rate of heterogeneous reactions than to the, necessary “energy”, which is commonly used. The Criado’s master curves indicated two different degradation mechanisms for the fibers: diffusion followed by random nucleation. The results also indicated that the crystallinity index as calculated by X-ray diffraction and determinated by FTIR does not necessarily represent higher thermal stability as noted by the thermogravimetric analysis curves. The thermal behavior and the degradation mechanism did not show to be influenced by the lignocellulosic components of the fibers, exception for buriti and sisal. This behavior was attributed to higher extractive content.     

Thermal analysis of less common lignocellulose fibers

The thermal behavior of four unusual lignocellulose fibers — namely Caroa, Curaua, Piassava and Sponge gourd — is described. Caroa and Curaua fibers showed a more homogeneous thermal degradation, with a single peak dominating in the DTG curve. Piassava and Sponge gourd showed two separated peaks, revealing the more pronounced amounts of hemicellulose present at these fibers. All four fibers are, however, thermally stable up to temperatures of around 200°C. The activation energies for the thermal degradation of the fibers were similar, except for the Caroa fiber. The lower activation energy associated to this fiber was attributed to its higher hemicellulose to cellulose ratio.     

TG studies of a composite solid rocket propellant based on HTPB-binder

Thermal decomposition kinetics of solid rocket propellants based on hydroxyl-terminated polybutadiene-HTPB binder was studied by applying the Arrhenius and Flynn-Wall-Ozawa's methods. The thermal decomposition data of the propellant samples were analyzed by thermogravimetric analysis (TG/DTG) at different heating rates in the temperature range of 300-1200 K. TG curves showed that the thermal degradation occurred in three main stages regardless of the plasticizer (DOA) raw material, the partial HTPB/IPDI binder and the total ammonium perchlorate decompositions. The kinetic parameters E _a (activation energy) and A (pre-exponential factor) and the compensation parameter (S _p) were determined. The apparent activation energies obtained from different methods showed a very good agreement. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal degradation of PVC cable insulation studied by simultaneous TG-FTIR and TG-EGA methods

Thermogravimetry (TG/DTG) coupled with evolved gas analysis (MS detection) of volatiles was used to characterize the thermal behavior of commercial PVC cable insulation material during heating in the range 20-800°C in air and nitrogen, respectively. In addition, simultaneous TG/FTIR was used to elucidate chemical processes that caused the thermal degradation of the sample. A good agreement between results of the methods was found. The thermal degradation of the sample took place in three temperature ranges, namely 200-340, 360-530 and 530-770°C. The degradation of PVC backbone started in the range 200-340°C accompanied by the release of HCl, H₂O, CO₂ and benzene. The non-isothermal kinetics of thermal degradation of the PVC cable insulation in the temperature range 200-340°C was determined from TG results measured at heating rates of 1.5, 5, 10, 15 and 20 K min^-1 in nitrogen and air, respectively. The activation energy values of the thermal degradation process in the range 200-340°C of the PVC cable insulation sample were determined from TG results by ASTM method. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetic thermal analytical study of saturated mono-, di- and tri-glycerides

A thermal degradation study using TG–DTG thermogravimetry was performed on three saturated fatty acids esterified with glycerol (i.e. glyceryl-tristearate (C₁₈), -tripalmitate (C₁₆) and -trimyristate (C₁₄)) at different heating rates. In addition, thermogravimetry (TG) and derivative thermogravimetry (DTG) of glyceryl di-stearate and glyceryl mono-stearate were also carried out at different heating rates. A deconvolution procedure applied to the first process and overlapping at least two steps between about 200 and 350 °C, enabled the activation energy of decomposition to be determined both by the Kissinger and the Ozawa–Flynn–Wall isoconversional methods for the deconvoluted steps of the above-mentioned fatty acids.     

Dynamic and Isothermal Thermogravimetric Degradation of Poly(vinyl Chloride)/Chlorinated Poly(ethylene) Blends

The thermal degradation of poly(vinyl chloride)/chlorinated poly(ethylene) (PVC/CPE) blends of different compositions was investigated by means of dynamic and isothermal thermogravimetric analysis in flowing atmosphere of nitrogen. Kinetic parameters (the apparent activation energy E, and pre-exponential factor Z) were calculated after Flynn-Wall-Ozawa method for the first stage of dynamic degradation of PVC/CPE blends, and after Flynn method for the isothermal degradation. In both cases, there is the compensation dependence between the values E and logZ. The values of compensation ratios as well as the characteristics of TG and DTG curves, confirm the stabilizing effect of CPE on PVC dehydrochlorination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal characterization and electrical properties of Fe-modified cellulose long fibers and micro crystalline cellulose

Thermal properties of polylactic acid (PLA) filled with Fe-modified cellulose long fibers (CLF) and microcrystalline cellulose (MCC) were studied using thermo gravimetric analysis (TG), differential scanning calorimetry, and dynamic mechanical analysis (DMA). The Fe-modified CLFs and MCCs were compared with unmodified samples to study the effect of modification with Fe on electrical conductivity. Results from TG showed that the degradation temperature was higher for all composites when compared to the pure PLA and that the PLA composites filled with unmodified celluloses resulted in the best thermal stability. No comparable difference was found in glass transition temperature (T _g) and melting temperature (T _m) between pure PLA and Fe-modified and unmodified CLF- and MCC-based PLA biocomposites. DMA results showed that the storage modulus in glassy state was increased for the biocomposites when compared to pure PLA. The results obtained from a femtostat showed that electrical conductivity of Fe-modified CLF and MCC samples were higher than that of unmodified samples, thus indicating that the prepared biocomposites have potential uses where conductive biopolymers are needed. These modified fibers can also be tailored for fiber orientation in a matrix when subjected to a magnetic field.     

Isothermal crystallization kinetics and thermal behavior of poly(?-caprolactone)/multi-walled carbon nanotube composites

This study describes the preparation of poly(?-caprolactone) (PCL)/multi-walled carbon nanotube (MWCNT) composites by ultrasonically mixing the PCL and as-fabricated MWCNT in a tetrahydrofuran solution. The TEM images show that the MWCNT is well separated and uniformly distributed in the PCL matrix. Differential scanning calorimetry (DSC), thermogravimetric analyzer (TGA), X-ray diffraction (XRD) and polarized optical microscopy (POM) were used to investigate the isothermal crystallization kinetics, crystalline structure and thermal behavior of PCL and PCL/MWCNT nanocomposites. DSC isothermal results revealed that the activation energy of PCL extensively decreases with increasing MWCNT contents, suggesting that the loading of MWCNT into PCL matrix probably induced heterogeneous nucleation during crystallization processes. From TGA data, the addition of small amount of MWCNT into PCL matrix can improve the thermal stability of PCL matrix. TGA isothermal degradation data illustrate that the activation energy E_d of the composites is smaller than that of PCL. This phenomenon can be attributed to the incorporation of more MWCNT loading into PCL caused a decrease in the degradation rate and an increase in the residual weight for PCL/MWCNT nanocomposites.     

Thermogravimetric Analysis of Cobalt(II)-dothiepin Complexes

The complexes of cobalt(II) with dothiepin (DOT) hydrochloride have been studied for kinetics of thermal degradation by thermogravimetric analysis (TG) and derivative thermogravimetric studies (DTG) in a static nitrogen atmosphere at a heating rate of 10° C min⁻¹. A general mechanism of thermal decomposition is advanced involving dehydration and decomposition process for both organic and inorganic ligands. The thermal degradation reactions were found to proceed in three steps having an activation energy in the range 6.75–170 kJ mol⁻¹. Thermal decomposition kinetics parameters were computed on the basis of thermal decomposition data. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal decomposition kinetics of natural fibers: Activation energy with dynamic thermogravimetric analysis

Dynamic TG analysis under nitrogen was used to investigate the thermal decomposition processes of 10 types of natural fibers commonly used in the polymer composite industry. These fibers included wood, bamboo, agricultural residue, and bast fibers. Various degradation models including the Kissinger, Friedman, Flynn-Wall-Ozawa, and modified Coats-Redfern methods were used to determine the apparent activation energy of these fibers. For most natural fibers approximately 60% of the thermal decomposition occurred within a temperature range between 215 and 310 °C. The result also showed that an apparent activation energy of 160-170 kJ/mol was obtained for most of the selected fibers throughout the polymer processing temperature range. These activation energy values allow developing a simplified approach to understand the thermal decomposition behavior of natural fibers as a function of polymer composite processing.     

Thermal degradation behavior of cellulose fibers partially esterified with some long chain organic acids

The thermal degradation behavior of cellulose fibers and some fibrous cellulose esters with partial degree of substitution has been studied by thermogravimetry analysis (TG) and differential scanning calorimetry (DSC). Cellulose esters were prepared by heterogeneous esterification in Py/TsCl with unsaturated or saturated long chain organic acids [undecylenic (C₁₁), undecanoic (C₁₁), oleic (C₁₈) and stearic (C₁₈)]. The thermal degradation of cellulose fibers follows a one-step process. The thermal stability of cellulose esters is inferior to that of unmodified cellulose fibers and the thermograms show a two-step degradation process, probably controlled by crosslinking reactions, which occur during thermal decomposition. Exothermic peaks in the DSC thermograms are also an indication of such reactions. Kinetic parameters such as the activation energy E, order of decomposition n, and frequency factor Z were obtained following the Friedman method. The cellulose sample followed first order of decomposition, however for cellulose esters higher orders were observed.     

草酸镁二水合物的非等温热分解动力学

The thermal decomposition of the magnesium oxalate dihydrate in a static air atmosphere was investigated by TG-DTG techniques. The intermediate and residue of each decomposition were identified from their TG curve. The kinetic triplet, the activation energy E, the pre-exponential factor A and the mechanism functionsf（a） were obtained from analysis of the TG-DTG curves of thermal decomposition of the first stage and the second stage by the Popesou method and the Flynn-Wall-Ozawa method.