Determination of amitraz and its degradation products and monitoring degradation process in quince and cucumber

Amitraz is a non-systemic acaracide and insecticide. Current maximum residue limits for amitraz are stated as ‘Amitraz including the metabolites containing the 2,4-dimethylaniline moiety’. Therefore, determination of amitraz and its all degradation products are important. In this study, we develop a gas chromatography/mass spectrometry (GC/MS) method for determination of amitraz and its degradation products 2,4 dimethylaniline (DMA), 2,4 dimethylformamidine (DMF) and N-(2,4-dimethyl phenyl)-N’-methylformamidine (DMPF) in cucumber and quince. The mechanism of the degradation process was monitored at different temperatures. Amitraz and its degradation products were extracted using the QuEChERS method. To determine amitraz and its degradation products, we used GC/MS. Quantification was carried out by using selected ion monitoring, and total ion chromatogram was used to monitor additional degradation products. The method was validated by studying linearity, limit of detection (LOD) and limit of quantification (LOQ), recovery and precision. The mechanism of the degradation process was monitored at different temperatures. Degradation of amitraz mainly to three degradation products, namely DMA, DMF and DMPF, increased with temperature. Besides these three main degradation products, two other new degradation products were detected.     

Degradation study on the thermally stable nickel phthalocyanine sheet polymer

Poly (nickel phthalocyanine) which has exceptional thermal stability is synthesized. Knowledge of modes of degradation of this polymer is found to be necessary for its high temperature applications. This polymer showed very high thermal stability with maximum polymer decomposition temperatures (PDT_max) of 500 °C in air and 890 °C in N₂, with char yield 93% at 800 °C. Because of its excellent thermal stability, degradation study with MS as well as GC–MS techniques were found to be very difficult. The present publication deals with MS and GC–MS studies of nickel phthalocyanine sheet polymer at high temperatures ranging from 700 to 1000 °C. Tentative mechanisms are proposed for its modes of fragmentations and based on GC–MS studies, the most probable degradation products are identified.     

Application of pyrolysis-capillary gas chromatography with NPD detection in thermal degradation of polyphosphazenes study

Polyphosphazenes represent a unique class of polymers with a backbone composed of alternating phosphorous and nitrogen atoms. The thermal behaviour and decomposition of a variety of polyphosphazenes depends on the type of side groups present. Especially those that bear aryloxy side groups, possess a high temperature stability as well as excellent flame resistance. Pyrolysis-capillary gas chromatography has been used in a study of three polyphosphazene samples for thermal stability characterisation. Degradation products were detected with three single detectors for flame ionisation (FID), nitrogen-phosphorous sensitivity (NPD) and mass spectrometry (MSD) at different pyrolysis temperatures ranging from 300°C up to 800°C. The NPD responses for phosphorous or nitrogen fragments of polyphosphazenes have been used for the construction of degradation product schemes and the examination of the thermal stability of the polyphosphazene’s backbone. Partial identification of the degradation products present in the gaseous phase was achieved by MSD. The polyphosphazenes thermal degradation conversion rates were at a maximum at 450–500°C. At various pyrolysis temperatures, the calculated N/P peak area ratio is a function of the degree of polyphosphazene-N=P-chain degradation, and reflective of the nitrogen — phosphorous detector sensitivity. NPD proved to be suitable tool for characterization of polyphospazene thermal stability.     

Calorimetric determination of head-to-head defect in poly(vinylidene fluoride)

Differential scanning calorimetric analyses were conducted on samples of poly(vinylidene fluoride) polymerized in an autoclave by tributylborane-oxygen by free-radical initiation at low temperature (-70-0°C). The peak melting points and the percent head-to-head defect in each polymer sample were determined by a reported calorimetric method. A commercial sample showed a melting temperature in the range 157–162°C and a percent head-to-head defect of 7.7%; whereas two experimental samples showed melting temperatures in the range 172–179°C with a percent head-to-head defect of 4.4 and 4.9%. The calorimetric procedure was modified by reducing annealing times to only 2 h, which saves time and, as shown in this study, avoids thermal polymer degradation.     

Rearrangement of the main-chain and subsequent thermal degradation of polyphenylene-ether

Studies of the thermal rearrangement and degradation of polyphenylene-ether (PPE) have been carried out by TGA (thermo-gravimetric analysis), GC-MS (gas chromatography-mass spectroscopy) and ¹H-NMR. 2,6-Xylenol was a major scission product in the temperature range 420–700 °C, and 3,5-xylenol, as a scission product, decreased with increasing temperature. Four monomeric and eight dimeric scission products were observed at relatively high temperatures. The distribution of the scission products, which changed with increasing temperature, led to the suggestion that rearrangement of the PPE main-chain occurred to form diphenyl methylene groups, followed by thermal degradation.     

The effect of melt-processing on the degradation of selected polyhydroxyacids: polylactides, polyhydroxybutyrate, and polyhydroxybutyrate-co-valerates

A series of resorbable polyhydroxyacids were studied by size exclusion chromatography (SEC), viscosity measurements, and differential scanning calorimetry (DSC) for the effect of the injection moulding process on the molecular weight and thermal properties of the polymers. The polymers studied were polylactides (PLA), polyhydroxybutyrate (PHB) and polyhydroxybutyrate-co-valerate (PHB/VA) (5–22% VA content). All polylactides underwent extensive degradation, in the range of 50–88%, and an increase in molecular weight distribution (MWD) following injection moulding at temperatures ranging from 130 to 215°C. In contrast to the polylactides, the decrease in molecular weight of the PHB and PHB/VA polymers after injection moulding at temperatures from 135 to 160°C was less dramatic, in the range of 4–53%. This was accompanied by a decrease of the MWD. No evidence for low molecular weight non-volatile degradation products was observed. Injection moulding led to a decrease in the melting temperature (T_m) and the heat of melting (ΔH_m) of PLA. Conversely, the moulding process did not significantly affect the melting temperature and heat of melting of polyhydroxybutyrate/valerates.     

Degradation of benzoic acid and its derivatives in subcritical water

In this research, the stability of benzoic acid and three of its derivatives (anthranilic acid, salicylic acid, and syringic acid) under subcritical water conditions was investigated. The stability studies were carried out at temperatures ranging from 50 to 350 °C with heating times of 10–630 min. The degradation of the benzoic acid derivatives increased with rising temperature and the acids became less stable with longer heating time. The three benzoic acid derivatives showed very mild degradation at 150 °C. Severe degradation of benzoic acid derivatives was observed at 200 °C while their complete degradation occurred at 250 °C. However, benzoic acid remained stable at temperatures up to 300 °C. The degradation products of benzoic acid and the three derivatives were identified and quantified by HPLC and confirmed by GC/MS. Anthranilic acid, salicylic acid, syringic acid, and benzoic acid in high-temperature water underwent decarboxylation to form aniline, phenol, syringol, and benzene, respectively.     

Process design methodology for organometallic chemistry in continuous flow systems

This publication summarises the methodology applied in the process design and scale up of fast, exothermic reactions using organometallic reagents for synthesis of intermediates in the production of Active Pharmaceutical Ingredient (API). Process understanding was developed by calculation of the kinetic parameters of the desired reactions and subsequent degradation of the reaction products along with calorimetric understanding. A reaction model, developed in silico, was used to specify process parameters to maximise yield and limit product degradation. The designed process operates with pseudo-adiabatic reaction conditions, from ambient temperatures with negligible impurity formation.     

Development and validation of a reversed phase HPLC method for quantitative analysis of bis-isoxazolylnaphthoquinone

The goal of this study was to determine the kinetic parameters involved in the decomposition of 2-(5-methyl-4-isoxazolylamino)-N-(5-methyl-4-isoxazolyl)-1,4-naphthoquinone-4-imine (1) in aqueous solution and to identify the main degradation products. An isocratic HPLC assay was used to study the degradation rate of 1. The products of hydrolysis were identified by comparison of their retention times with those of authentic samples. The amount of 1 and the two degradation products resulting from storage of 1 in various buffer solutions was followed in function of time by a reversed-phase HPLC stability-indicating method. The observed degradation rates followed pseudo-first-order kinetics at constant pH, temperature and ionic strength. The log k–pH-profile was constructed at 35°C from the first-order rate constants obtained from studies at pH values ranging from 0.88 to 10.80 (μ=0.5 M). Hydrolysis in the acidic and alkaline media resulted in the formation of two degradation products in each case. The pH-rate profile of 1 in buffer solution was adequately described using a four-term rate equation. The obtained pH-rate profile indicated specific acid–base catalysis with a region of maximum stability between pH 6.40 and 7.40 which can be adequate for formulations of 1.     

Products of low-temperature pyrolysis of nanocellulose esters and implications for the mechanism of thermal stabilization

Esterification was used to improve the thermal stability of nanocellulose to extend its application as reinforcing filler to polymer matrices with high melting point. The effect of the structure of ester groups on thermal stability was studied in detail. Various types of nanocellulose esters (straight-chain, C2–C14; cyclic adamantoyl, ADM; aromatic benzoyl, BNZ; and branched pivaloyl, PIV) with degree of substitution values in the range of 0.40–0.47 were prepared from bacterial cellulose nanofibers and nanocrystals. The reaction conditions used to prepare the esters maintained the viscosity-average degree of polymerization (DPv) and crystallinity of the starting materials. Thermogravimetric analysis showed that the temperature at maximum weight loss rate (T_max) increased after esterification. The structure of the ester groups and the DPv, however, showed no varying effect on T_max. The 5 % weight loss temperature (WLT) which was used to assess the thermal stability at the onset of thermal degradation varied with the type of ester. Lower 5 % WLT was observed in straight-chain esters than those of the bulky esters of ADM, BNZ and PIV; which also showed high resistance to weight loss when subjected to isothermal heating. To understand the event at the onset of thermal degradation, low temperature pyrolysis was conducted. The evolved gases were separated and identified by gas chromatography–mass spectrometry technique. Results showed that at the onset of thermal degradation, levoglucosan (LG) is produced from the untreated BC nanocrystals. After esterification, LG formation was inhibited. The removal of the ester groups or deprotection is the main event at the onset of thermal degradation of nanocellulose esters. From the structure of the pyrolysis products, the mechanism of thermal deprotection of nanocellulose esters is proposed for the first time.     

Calorimetric investigations of the hydrolytic degradation for a series of β-sultams

The hydrolytic degradation of four β-sultams was investigated using isothermal microcalorimetry to determine kinetic and enthalpic data. Firstly, all four compounds were analysed in the solid-state at 310 K, with a significant substituent-based stabilising/destabilising effect being observed. Secondly, the four compounds were analysed in the presence of pH 4 acetate buffer, at three temperatures (298, 310 and 323 K). Under these conditions, the substituent choice affected the rate of hydrolysis and the associated change in enthalpy for each compound. Based on the calorimetric data presented in this work, no change in reaction mechanism for the hydrolytic degradation was observed over the temperature range considered.     

Photodegradation of polyethylenes: Comparative effect of Fe and Ca-stearates as pro-oxidant additives

The effect of iron and calcium stearates on the degradation of polyethylene (LDPE and LLDPE), under natural and artificial exposure, has been studied. The activity of stearates has been evaluated by chemiluminescence and FTIR of polyethylenes. The analysis of the molecular weight changes and content of degradation products identified by GC-MS during ageing process confirmed their pro-degrading activity. Films containing stearates exhibited lower CL emission, and revealed the higher efficiency of Fe-Stearate compared to Ca-Stearate in decomposing hydroperoxides, leading to higher degradation during processing. The results were confirmed by TGA analysis, where the weight loss onset and T_max shifted to lower temperatures in polyethylenes with incorporation of Fe- and Ca-stearates compared to pure polymers.Polyethylenes were outdoor and accelerated exposed, and CL measured at different period of times. Chemiluminescence temperature-ramping tests under nitrogen showed the formation of a peroxide peak at lower temperature, and a significant increase in carbonyl index for PE containing stearates was found by FTIR. The results were supported by GC-MS, where the concentration of extracted products identified in the polyethylenes containing Fe-stearate was significant, and a much greater decrease in molecular weight was determined by GPC, which confirmed the development of degradation for polyethylenes with Fe-Stearates in comparison to pure or Ca-stearate polyethylenes.     

Thermal analysis and crystallinity study of cellulose nanofibril-filled polypropylene composites

The isothermal and non-isothermal decompositions of cellulose nanofiber (CNF) and microfibrillated cellulose (MFC)-filled polypropylene (PP) composites were evaluated and compared with microcrystalline cellulose (MCC)-filled composites by means of thermogravimetric analysis (TG). X-ray diffraction was employed to evaluate crystallinity of the composites. The degree of maximum thermal degradation (ultimate DTG peak value) increased and thermal degradation onset temperature decreased as the cellulose content increased because the thermal stability of cellulose fillers is lower than that of neat PP, but the thermal degradation of the composite was hindered at higher temperature conditions because of the increased residual mass content of the cellulose nanofibril fillers compared to the matrix polymer. The isothermal residual mass of the cellulose nanofibril-filled PP composites under melt blending and injection molding temperatures was decreased marginally by incorporation of the cellulose reinforcement but still exhibited considerable isothermal stability. The raw materials and composites examined in this study were not affected by the manufacturing process temperatures utilized to produce the composites. The MCC decreased the composite crystallinity while the nano-sized cellulose (CNF and MFC) did not appear to have an effect on crystallinity.     

Exactly alternating silarylene–siloxane polymers. VII. Thermal stability and degradation behavior of p-silphenylene–siloxane polymers with methyl,vinyl, hydrido,and/or fluoroalkyl side groups

The thermal stability and degradation behavior of a series of nine different exactly alternating silphenylene-siloxane polymers which contained methyl, vinyl, hydrido, 3,3,3-trifluoropropyl, and tridecafluoro-1,1,2,2-tetrahydrooctyl side groups, or their combinations, were investigated by dynamic and isothermal gravimetric analyses in air and in nitrogen. Two distinctly different mechanisms were observed in these atmospheres: a complex multi-step weight loss process in air and a single-step process in nitrogen. In nitrogen all polymers produced black, insoluble, highly stable degradation residues which were characterized by high carbon content. In contrast, in air the nonfluorine containing polymers degraded to pure silica, while the fluoroalkyl substituted polymers may have formed fluorosilicates of unspecified structures. There appears to be no significant molecular weight effect on the thermal stability of these polymers, at least not above an M _w value of about 35,000. Isothermal investigations indicate that 300°C in air and 350°C in nitrogen may be possible upper use temperatures for the methylvinyl substituted, exactly alternating silphenylene–siloxane polymers for extended periods of time. A strong thermostabilizing effect by vinyl side groups on the degradation behavior of these polymers was established. The extent of stabilization depends on the content of vinyl units, but it can already be clearly seen at the 5 mol % vinyl level, and it increases exponentially with increasing vinyl concentration. In contrast to this behavior, by comparison with the parent all-methyl substituted, exactly alternating silphenylene–siloxane polymers, the hydrido and fluroalkyl side groups reduce overall polymer thermal stability in terms of the degradation onset temperature, the temperature for 50% weight loss, and the amount of degradation residue. The presence of these groups also extends the later stages of the degradation processes to higher temperatures. Based on these and previous results, an order of stability is proposed as a function of the type of the substituent side groups for the thermal degradation of these polymers.     

Thermo‐mechanical Properties of PEO‐PU/PAN Semi‐Interpenetrating Polymer Networks and their LiClO4 Salt‐Complexes

This paper is an investigation on the thermo‐mechanical properties of a new class of materials, which holds promise for its potential use as solid polymer electrolytes, i.e., SPE material. A series of poly(ethylene oxide)‐polyurethane/poly(acrylonitrile) (PEO‐PU/PAN) semi‐IPNs, along with their LiClO₄ salt complexes, were characterized for their thermal, mechanical and dimensional stability using DSC, TG‐DTA, UTM and DMTA. The glass transition temperature (T_g) of both the undoped and doped semi‐IPNs, obtained by DSC, remained well below room temperature (～?50°C to ?35°C), satisfying one of the essential requirements to serve as a SPE host matrix. The crystallization process in the PEO segments of the PEO‐PU/PAN semi‐IPNs was prevented at higher salt concentrations, which is attributed to the Li⁺ ion mediated pseudo‐crosslinks. Good thermal stability of the semi‐IPNs was evident from the degradation onset temperature (T₀～240°C) with a three‐stage degradation process, which is independent of the PAN content as observed from differential thermogravimetric studies. The incorporation of PAN in the PEO‐PU networks results in improved mechanical properties, such as tensile strength and modulus while retaining the flexibility of the semi‐IPNs. The peak temperatures and storage modulus obtained from DMTA correlates well with the observations of DSC and tensile measurements.     

Study of the influence of water absorption on different epoxy-diamine systems by DSC

The diffusive, calorimetric and thermal degradation behavior of different epoxy-amine systems was investigated during water sorption at different temperatures (23, 40 and 70°C). Experimental results showed that the water absorption at these temperatures fitted well to Fick’s law. Influence of water immersion during different periods of time on the glass transition temperatures was studied by differential scanning calorimetry. Thermal degradation of saturated samples was studied by thermogravimetric analysis. Dependence on the selected curing cycle was also checked.     

Calorimetric glass transitions in the amorphous forms of water: a comparison

The calorimetric glass transition behaviour in the amorphous forms of water is reviewed: for a heating rate of 30 K min⁻¹ the onset temperature, or T_g, of the glass transition is 136±1 K for hyperquenched glassy water and annealed vapour-deposited amorphous solid water, and 129±1 K for the low-density form of pressure-amorphized hexagonal ice. The increase in heat capacity in the glass transition region is between 1.6–2 J K⁻ mol⁻ for the three amorphous forms. Annealing of the samples a few degrees below T_g or heating several degrees above the glass transition region has no influence on the onset temperatures at 136 K and 129 K respectively, which is contrary to ‘normal’ behaviour. The results are discussed with respect to the ‘structure’ of the three amorphous forms of water below the glass transition region and a “gel-like” state of water above T_g.     

Thermo-oxidative stability of polypropylene/layered silicate nanocomposites

Several series of experiments were carried out to check the effect of components on the stability of PP/layered silicate nanocomposites. The amount of organophilic montmorillonite (OMMT) changed between 0 and 6, while that of maleated polypropylene (MAPP) between 0 and 50 vol%. The composites were prepared in an internal mixer at 190 °C. Mixing speed and time were changed to study the effect of processing conditions on stability. The structure of the samples was characterised by various methods, while stability by the induction time of oxidation (OIT), the onset temperature of degradation (OOT) and by colour. Contrary to numerous claims published in the literature, which indicate the positive effect of layered silicates on the stability of polymer nanocomposites, our results clearly proved that both OMMT and MAPP accelerate degradation during processing and deteriorate the properties of PP composites. Residual stability decreases drastically with increasing amounts of both components, chain scission leads to the decrease of viscosity and to inferior strength and deformability. In spite of expectations, the effect of the components is independent of each other. Discoloration is caused mainly by the inherent colour of the filler and it decreases with increasing exfoliation. The most probable reason for decreased stability is the reaction of the components with the stabilisers, but this explanation needs further verification. Processing conditions influence degradation considerably, increasing shear rate and longer residence times lead to more pronounced degradation. The basic stabilization of commercial grade polypropylenes is insufficient to protect the polymer against degradation and without additional stabilization processing under normal conditions results in products with inferior quality.     

Thermal degradation studies of polyurethane/POSS nanohybrid elastomers

Reported here is the synthesis of a series of polyurethane/POSS nanohybrid elastomers, the characterisation of their thermal stability and degradation behaviour at elevated temperatures using a combination of thermogravimetric Analysis (TGA) and thermal volatilisation analysis (TVA). A series of PU elastomer systems have been formulated incorporating varying levels of 1,2-propanediol-heptaisobutyl-POSS (PHIPOSS) as a chain extender unit, replacing butane diol. The bulk thermal stability of the nanohybrid systems has been characterised using TGA. Results indicate that covalent incorporation of POSS into the PU elastomer network increases the non-oxidative thermal stability of the systems. TVA analysis of the thermal degradation of the POSS/PU hybrid elastomers have demonstrated that the hybrid systems are indeed more thermally stable when compared to the unmodified PU matrix; evolving significantly reduced levels of volatile degradation products and exhibiting a ∼30 °C increase in onset degradation temperature. Furthermore, characterisation of the distribution of degradation products from both unmodified and hybrid systems indicate that the inclusion of POSS in the PU network is directly influencing the degradation pathways of both the soft and hard-block components of the elastomers: The POSS/PU hybrid systems show reduced levels of CO, CO₂, water and increased levels of THF as products of thermal degradation.     

Viscoelastic and thermal characterization of crosslinked PVC

Soft PVC is employed for the manufacturing of a wide range of products with different properties and a relatively low cost. The utilization of soft PVC is restricted by the poor thermal, chemical and mechanical resistance properties. Also, plasticizer migration can modify the properties or can make useless the materials for some applications because of toxicity or a general loss of properties. PVC crosslinking is the most effective way to improve mechanical and transport properties of rigid or flexible PVC at high temperatures, but at the same time the thermal stability of PVC may be significantly reduced. In this work, the crosslinking reaction of plasticized poly(vinyl chloride) (PVC) through difunctional amines was studied. The mechanisms involved in the crosslinking reaction were explained by Fourier transform infrared (FTIR) analysis. The thermal activated crosslinking reaction was studied by cone and plate rheometry, analyzing the evolution of viscoelastic properties of the suspension as a function of time and temperature. The effect of the addition of crosslinking agents on the thermal stability of the polymer was studied by thermogravimetric analysis (TGA), which revealed that crosslinking reactions promote thermal degradation phenomena in the polymer matrix. This is attributed to the formation of HCl and other species promoting polymer degradation during crosslinking, thus leading to higher weight loss during thermal treatment with respect to unmodified PVC plastisols. This was also confirmed by an evident yellowing after crosslinking, especially at higher temperatures.