Thermo-oxidative Degradation Research Articles

Effects of de-polymerized lignin content on thermo-oxidative and thermal stability of polyethylene

This study demonstrated de-polymerized lignins to be cost-effective bio-substitutes for commercial antioxidant in plastics. In this work, effects of addition amounts of de-polymerized kraft lignin (DKL) and de-polymerized hydrolysis lignin (DHL) in polyethylene (PE) on its thermo-oxidative and thermal stability were investigated in air and N2 atmosphere, respectively. Due to the difference in the solubility characteristics of DKL and DHL in PE, the oxidation induction time and activation energy for thermo-oxidative degradation of the PE blend leveled off after 2.5 wt% addition of DKL content but increased in an almost linear manner with increase of DHL content. The results also revealed that the addition of 2.5 wt% of DKL or 5 wt% of DHL attained the same level of antioxidant activity as the addition of 0.5 wt% of Irganox 1010. In addition, PE without and with addition of 2.5 wt% of DKL were comparatively investigated by thermogravimetry analysis (TGA) analysis in air and N2 atmosphere (pyrolysis) and by Fourier Transform Infrared Spectroscopy (FT-IR), and the results showed that the addition of 2.5 wt% of DKL enhanced the thermo-oxidative and thermal stability of PE in both thermo-oxidative degradation and pyrolysis processes at above 400 °C.

Lightweight Poly(ε-Caprolactone) Composites with Surface Modified Hollow Glass Microspheres for Use in Rotational Molding: Thermal, Rheological and Mechanical Properties.

In this work, novel composites based on poly(ε-caprolactone) (PCL) were prepared and characterized in terms of morphological, thermal, rheological and mechanical properties. Hollow glass microspheres (HGM), alone or surface modified by treatment with (3-aminopropyl)triethoxysilane (APTES) in order to enhance the compatibility between the inorganic particles and the polymer matrix, were used to obtain lightweight composites with improved properties. The silanization treatment implies a good dispersion of filler particles in the matrix and an enhanced filler–polymer adhesion. The addition of HGM to PCL has relevant implications on the rheological and mechanical properties enhancing the stiffness of the material. Furthermore, the presence of HGM strongly interferes with the crystallization behavior and thermo-oxidative degradation of PCL. The increase of PCL crystallization rate was observed as a function of the HGM amount in the composites. Finally, rotational molding tests demonstrated the possibility of successfully producing manufactured goods in PCL and PCL-based composites on both a laboratory and industrial scale.

Effect of an antioxidant on the life cycle of wood flour/polypropylene composites

This study assessed the life cycle of biocomposites with antioxidants by repeated processing. The effects of antioxidants on the life cycle of wood flour/polypropylene (PP) composites were determined by analyzing their mechanical and thermal properties. The composites were repeatedly processed for seven times with pelletizing and extruding. An antioxidant, pentaerythritoltetrakys 3-(3,5-ditert-butyl-4-hydroxyphenyl) propionate, was used. The mechanical strength of the biocomposites decreased after reprocessing. Fourier transformed infrared analysis showed that thermo-oxidative aging occurred during reprocessing. The thermal performance of the resulting composites decreased because of reprocessing. Wood flour/PP has a long lifetime and antioxidants can slow the thermo-oxidative and mechanical degradation during reprocessing.

A study of the thermal degradation of glass fibre sizings at composite processing temperatures

Although not fully understood, it is well recognized that optimal working of glass fibre sizings is necessary to maximize the performance of glass fibre reinforced polymer composites. It is important that the organic components in such sizings continue to function after exposure to the high temperatures often experienced during composite processing. This study presents the results on the thermal stability of polypropylene and epoxy compatible glass fibre sizings obtained using TGA, microbond adhesion measurement and composite mechanical testing. Test results indicate that the performance of commercial polypropylene compatible glass fibre sizings can be significantly compromised by thermo-oxidative degradation at normal composite processing temperatures. A significant reduction in composite performance is directly related to a loss of fibre-matrix adhesion caused by thermal degradation of some of the principal sizing components.

Kinetic triplet determination and modified mechanism function construction for thermo-oxidative degradation of waste polyurethane foam using conventional methods and distributed activation energy model method

Rapid growth of waste polymers attracts increasing attentions nowadays, and pyrolysis technology is acknowledged as an effective handling way. In this study, waste rigid polyurethane (RPU) was selected to conduct thermogravimetric analysis experiments with four different heating rates. Results showed that the thermo-oxidative degradation of RPU presents a two-main-stage process. Subsequently, thermal degradation kinetics were analyzed by model free, model fitting, and distributed activation energy model (DAEM) fitting methods. Isoconversional methods were used to obtain the apparent activation energy. Pyrolysis kinetic parameters were calculated through selected reaction models by model fitting method. Then the experimental kinetic function was obtained, based on which the proper theoretical reaction models were modified by the accommodation function. The best reaction model from the alternative reconstructed functions was optimized for two steps respectively. Distributed activation energy model was firstly introduced to fit the experimental data of RPU pyrolysis. The results of this study have implications concerning kinetic triplet determination method and reaction models modification, especially guiding to waste polymers pyrolysis kinetics and reaction model construction.

Thermo-oxidative degradation kinetics of renewable hybrid polyurethane–urea obtained from air-oxidized soybean oil

This study explores the synthesis and kinetics of non-isothermal thermo-oxidative degradation of renewable hybrid polyurethane (PU)–urea obtained from air-oxidized soybean oil. Fourier transformed infrared spectroscopy (FTIR) and thermogravimetry (TG) analyses were performed, aiming to verify chemical changes and the kinetics parameters using different approaches for the samples obtained. FTIR confirmed that a polymerization process occurred as well and modification in the relative hydrogen bonds is due to the formed urea groups that formed in the hybrid materials. TG analysis showed a dependence of the activation energy (using the FWO and KAS model-free methods) on the degree of conversion for all samples studied in three different degradation steps. The most probable degradation mechanism was tested by using a multivariate nonlinear regression by using the F statistical test. For all samples, the autocatalytic model successfully described the thermo-oxidative degradation, which is in accordance with the chemical degradation process for polyurethanes. Finally, thermal degradation in the time function was estimated and more satisfactory results were obtained by comparing the literature data for similar systems. So, it was possible to obtain reliable and consistent results of the kinetic parameters, which are essential for academic and industrial purposes.

Thermal Properties of Porous Polylactide

The melting and thermal degradation of porous polylactide have been studied by differential scanning calorimetry and thermogravimetric analysis. The pores are formed from a solution of azobisizobutyronitrile in acetone and ammonium carbonate in a water–acetone mixture and thermostatting of the filled polymer and via exposing the samples to a medium of supercritical carbon dioxide. It has been shown that the blowing agents destroy the crystalline regions of the polymer and decrease the melting point and heat of fusion of the crystallites depending on the plasticizing impact on the polymer matrix, the pore formation method, and the nature of the blowing agent. Pore formation in polylactide leads to a decrease in the initial thermooxidative degradation temperature of the polymer and a change in the process mechanism.

Thermal and thermo-oxidative degradation kinetics and characteristics of poly (lactic acid) and its composites

Thermal degradation behavior and kinetics of starch/PLA composites in an inert and oxygen atmosphere were investigated by TG and TG-FTIR techniques. It is shown that the thermal degradation process can be divided into three stages, and a significant difference between thermal and thermo-oxidative degradation is the third stage in which the residual chars are further cracked for the thermo-oxidative degradation. The activation energy was calculated using the iso-conversional Flynn-Wall-Ozawa (FWO) method. The lower activation energy for thermo-oxidative degradation indicated that oxygen had an accelerated effect on thermal degradation. The variation of activation energy indicated that the decomposition of all the samples was a complex process that included at least two different mechanisms. Evolution of the evolved gaseous products with temperature was studied to understand the thermal and thermo-oxidative decomposition comprehensively. According to the TG-FTIR analysis, the gaseous products mainly contained lactide, cyclic oligomers, aldehydes, CO2, CO, and H2O.

Flame retardant effect and mechanism of a novel DOPO based tetrazole derivative on epoxy resin

A novel highly efficient flame retardant with phosphaphenanthrene group and tetrazole ring, 6-(((1H-tetrazol-5-yl)amino)(4-hydroxyphenyl)methyl)dibenzo[c,e][1,2]oxaphosphinine 6-oxide (ATZ), was synthesized and incorporated into epoxy matrix as co-curing agent to remarkably improve the flame retardancy of epoxy resin. The curing behaviors of epoxy systems were investigated by non-isothermal differential scanning calorimetry (DSC) tests. The thermal and flame retardant properties of epoxy thermosets were studied by thermogravimetric analysis (TGA), DSC analysis, limiting oxygen index (LOI), UL-94 and cone calorimeter test. Moreover, the flame retardant mechanism was comprehensively investigated by analyzing the thermo-oxidative degradation and pyrolysis behaviors, along with the morphology and structure of residual char of epoxy thermosets. It showed that ATZ could accelerate the crosslinking reaction of epoxy system. The incorporation of ATZ resulted in the decrease of glass transition temperature (Tg) and initial degradation temperature, while the increase of char yield at high temperature of epoxy thermoset. With the incorporation of 6 wt% ATZ, the thermoset achieved an LOI value of 33.7% and V-0 rating in UL-94 test. Moreover, the peak heat release rate (PHRR) in cone calorimetry test decreased by 26% in comparison with that of neat EP, accompanied with lower total heat release (THR) and total smoke production (TSP). The flame retardant mechanism was ascribed to the barrier effect of intumescent and compact phosphorus-rich char layers with honeycombed cavity structure inside in the condensed phase, and quenching effect of phosphorous radicals and diluting effect of nonflammable gases in the gas phase. The interesting blowing out effect observed during UL-94 test arose from the intensive release of pyrolytic gases with considerable phosphorous radicals and nonflammable gases from the surface of sealed char layers.

Thermooxidative Degradation of Composites Based on Epoxy Resin and Metal Nanopowders

The thermooxidative degradation behavior of the epoxy composites filled with metal nanopowders has been investigated by thermogravimetric analysis under nonisothermal conditions in air atmosphere. The mechanical characteristics of epoxy composites were also studied by three-point bending method. The comparison of two different types of metal nanopowder was made. Aluminum and copper nanopowders prepared by electrical explosion of wires were used as fillers separately as well as in combination with conventional fame-retardant boric acid. It was shown that aluminum nanopowder increased slightly thermal stability of the epoxy composites. On the contrary, the introduction of copper nanopowder in epoxy resin led to rapid degradation of the epoxy composite. The combination of metal nanopowders and boric acid improved thermal stability of the epoxy composites. The highest flexural properties showed the epoxy composite filled with copper nanopowder.

Oxidative and non-oxidative degradation of a TDI-based polyurethane foam: Volatile product and condensed phase characterisation by FTIR and solid state 13C NMR spectroscopy

The oxidative and non-oxidative degradation behaviour of a flexible polyurethane foam, synthesised from toluene diisocyanate and a polyether polyol, is reported. Both toluene diisocyanate and diaminotoluene were identified as major products under non-oxidative conditions, which indicates that the urethane linkages are degrading by two competing degradation mechanisms. Degradation of the urethane linkage by a depolymerisation reaction to yield toluene diisocyanate and polyol is proposed to occur initially. In addition, the atmospheric pressure conditions favour the degradation of the urethane linkages via a six-membered ring transition state reaction to form diaminotoluene, carbon dioxide and alkene terminated polyol chains. Solid-state 13C NMR spectroscopy and elemental analysis of the residues indicates that at temperatures above 300 °C ring fusion of the aromatic components within the foam occurs, and this leads to a nitrogen-containing carbonaceous char which has a complex aromatic structure. It is proposed that under the confined conditions of the degradation the aromatic nitrogen-containing species, such as toluene diisocyanate and diaminotoluene, undergo secondary reactions and ring fusion to yield a complex char structure.Under oxidative conditions, degradation, including ring fusion, occurs at a lower temperature than under non-oxidative conditions. Neither toluene diisocyanate nor diaminotoluene were observed as major degradation products. The polyol is observed to undergo thermo-oxidative degradation at much lower temperatures than purely thermal degradation. As a consequence, the depolymerisation reaction via the six-membered ring transition state is limited in extent and diaminotoluene is not evolved. The absence of toluene diisocyanate is proposed to be a result of this species undergoing oxidative degradation reactions which lead to it being incorporated into the char.

Коррозионная стойкость газопламенных полимерных покрытий, модифицированных неорганическими добавками

Исследовано влияние концентрации и дисперсности микроразмерного неорганического модификатора (ситалл, алюминиевая пудра) на коррозионную стойкость полимерного композиционного материала (ПКМ) газопламенных покрытий на основе полиэтилентерефталата (ПЭТФ), полиэтилена высокого давления (ПЭВД) и полиамида (ПА-6). Получена зависимость уровня коррозионной стойкости от дисперсности и концентрации наполнителя.

Advancing the Use of High-Performance Graphene-Based Multimodal Polymer Nanocomposite at Scale.

The production of an innovative, high-performance graphene-based polymer nanocomposite using cost-effective techniques was pursued in this study. Well-dispersed and uniformly distributed graphene platelets within a polymer matrix, with strong interfacial bonding between the platelets and the matrix, provided an optimal nanocomposite system for industrial interest. This study reports on the reinforcement of high molecular weight multimodal-high-density polyethylene reinforced by a microwave-induced plasma graphene, using melt intercalation. The tailored process included designing a suitable screw configuration, paired with coordinating extruder conditions and blending techniques. This enabled the polymer to sufficiently degrade, predominantly through thermomechanical-degradation, as well as thermo-oxidative degradation, which subsequently created a suitable medium for the graphene sheets to disperse readily and distribute evenly within the polymer matrix. Different microscopy techniques were employed to prove the effectiveness. This was then qualitatively assessed by Raman spectroscopy, X-ray diffraction, rheology, mechanical testing, density measurements, thermal expansion, and thermogravimetric analysis, confirming both the originality as well as the effectiveness of the process.

Development of an accelerated artificial ageing method for the characterization of degradation products of antioxidants in lubricants by mass spectrometry.

The understanding of ageing mechanisms of antioxidants in base oils is indispensable for the development of improved lubricants. In this study, a novel artificial ageing method based on the application of peroxide as oxidant is presented for improved monitoring of thermo-oxidative degradation processes in combination with mass spectrometry. Model oils containing aminic and phenolic antioxidants were aged and chemical structures of their oxidation products were elucidated by ultrahigh performance liquid chromatography and electrospray ionization high resolution (Orbitrap) mass spectrometry. Additionally, synergistic mixtures of four antioxidants were investigated, because the formation of condensed molecules from amines and phenols would have a major influence on the antioxidant potential but could not be detected in the bulk lubricant.

Poly(dopamine) coated graphene oxide as multi-functional filler in waterborne polyurethane

Graphene oxide, known as an excellent reinforcing agent in polymer composites, was modified with dopamine and then incorporated into waterborne polyurethane (W-PU) via water solution blending. The addition of dopamine modified graphene oxide (D-GO) in W-PU is able to strengthen the stress transfer from the polymer matrix to the filler, and hence dramatically enhance the mechanical properties of the W-PU with increased ultimate Young’s modulus and moderately improved elongation at break. Also, since poly(dopamine) contains abundant phenolic groups in the structure, this project also aims to improve the antioxidant property of polyurethane. Impressively, it is found that the D-GO filler significantly slows down the rate of photo-degradation and thermo-oxidative degradation, lowering the drops of tensile stress, yield strain and elongation at break after UV irradiation. Besides, compared with neat PU and 1 wt% D-GO containing W-PU nano-composite, in which even no electrical conductivity can be observed, nano-composites containing 4 wt% D-GO exhibits a considerable electrical conductivity up to 0.82 S m−1. This work demonstrates that D-GO is not only a promising candidate in aiding PU as an impressive coating materials with excellent UV and thermal oxidation resistance, but also can act as an anti-static material.

Thermo-oxidative and thermal degradation kinetics of silica/polymethyl methacrylate composites with electrostatic interaction phase interfaces

Abstract The thermo-oxidative and thermal degradation kinetic parameters of polymethyl methacrylate-methacryloxyethyltrimethyl ammonium chloride/silica aerogel composites (PMMA-MTC/SA) were investigated in this paper and were compared with the thermal stability and thermal conductivity of different types of composites. As a composite with electrostatic interaction, the thermo-oxidative and thermal degradation activation energies (E) of PMMA-MTC/SA were 173.97 and 188.05 kJ/mol, respectively. The results indicated that the electrostatic interaction could indeed enhance the thermal stability of silica/polymethyl methacrylate composites on the premise of good mechanical properties and heat insulation performance. It is of great significance for the further development of silica-based thermal insulation composites.

Investigation of radio-oxidative ageing conditions on EVA/EPDM blends: Understanding the limitations posed as to representing long term in-use exposures

The effect of gamma-irradiation and temperature to accelerate, in a representative way, the ageing of EVA (Ethylene Vinyl Acetate)/EPDM (Ethylene Propylene Diene Monomer) blends was investigated. These blends constitute model materials of cable insulation used in Nuclear Power Plants (NPPs). Physicochemical evolutions of the blends were monitored by InfraRed (IR) spectroscopy, gel fraction measurements and Differential Scanning Calorimetry (DSC). After having pointed out the main similarities between the thermooxidative degradation (100 °C) and the radiooxidative degradation at room temperature, both stresses were combined to accelerate the ageing. It is shown that combining gamma-irradiation and high temperature, or subsequent thermooxidation after radiooxidation, accelerates the ageing but may cause distortion within the degradation mechanisms. These limitations of representativeness encountered are particularly due to an increase in chain scission reactions and formation of new crystallites in the blend.

Thermo-oxidative degradation of aromatic flavour compounds under simulated tobacco heating product condition

A modified pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) method was used to evaluate the thermo-oxidative degradation of 34 flavour compounds containing aromatic sub-units, in 9% oxygen / 91% nitrogen at 300 °C with 5 min isothermal holding. This set of pyrolysis parameter was used to simulate heated tobacco products. The main types of reactions of these aromatic species under these conditions were relatively mild oxidation and thermal division resulting in the formation of benzaldehyde and other aldehydes, ketones, and styrene. The highest yield of these products was estimated to be around 10%, occurring where the molecular structure and reactivity of the compound was susceptible to oxidation or bond scission. Representative reaction schemes were proposed to explain the formation of the detected products. The results proved that styryl moiety present in some aromatic flavour compound did not decompose to styrene under the conditions applied, rather, styrene was generated from phenylacetic acid and phenylethyl esters by thermal cleavage at 300 °C.

Influence of thermooxidative degradation on the in situ fate of polyethylene in temperate coastal waters

Polyethylene is a commonly used polymer in plastic products and is often found as marine litter. Nevertheless there is limited knowledge about what happens to the material when it ends up in the sea. Polyethylene films were therefore thermally oxidised to four different levels of degradation. The films were then placed in stainless-steel cages in the sea off the Swedish west coast for 12 summer weeks. Subsamples were analysed with respect to biofouling, degradation and buoyancy. All levels showed a continued oxidation in the field. The pre-degraded films started fragmenting and the non-degraded films showed a decrease in tensile strain. All levels showed increased biofouling with higher presence of filamentous algae and bryozoans on pre-degraded materials. The density (kg·m−3) of the films was seen to increase slightly, and the apparent density for the pre-degraded films (density of the films with biofilm) showed a strong increase, which resulted in sinking.

Thermo-oxidative stability of rubber magnetic composites cured with sulfur, peroxide and mixed curing systems

ABSTRACTRubber magnetic composites were prepared by incorporation of strontium ferrite into rubber matrices based on natural rubber (NR) and acrylonitrile butadiene rubber. The sulphur, peroxide and mixed sulphur/peroxide curing systems were applied for cross-linking of rubber compounds. The main goal of the work was to investigate the influence of the curing system composition on the physical–mechanical and magnetic properties of prepared composites. The thermo-oxidative stability of the composite materials was assessed by evaluation of thermogravimetric analysis and ageing test. The results showed that the composition of curing system influences the physical–mechanical properties of composites, but in strong dependence on the type of rubber matrix. After exposure of test sample to the conditions of thermo-oxidative ageing, the changes in composite properties were also recorded. The influence of thermo-oxidative degradation was more pronounced in the case of composites based on NR, where the sample cured only with peroxide system was almost completely degraded in the given conditions of ageing. On the other hand, the magnetic characteristics of composites seem to be influenced neither by curing system composition nor by ageing.