Thermal Oxidation Of Polymers Research Articles

Isothermal thermogravimetric method using a fast scanning calorimeter and its application in the isothermal oxidation of nanogram-weight polypropylene

Conventional thermogravimetry (TG) is a common method for studying thermal degradation and/or thermal oxidation of polymers. However, the temperature range for isothermal TG studies is limited to regions close to the melting temperature, where thermal degradation and/or thermal oxidation proceed slowly. Higher temperatures cannot be reached because thermal degradation and/or thermal oxidation start upon heating, even using the highest possible heating rate of the conventional TG. The method of fast scanning calorimetry (FSC) to obtain a quasi-real-time isothermal TG curve via a nanogram-weight sample (nano-TG method) was reported. During the 50 cycles of FSC measurements of polypropylene (PP) between room temperature and 300 °C, regardless of air flow, all FSC traces were consistent with each other (i.e., thermal oxidation of PP was fully suppressed during the fast scanning). On the other hand, when the sample was annealed for a few seconds at 300 °C during the cyclic FSC runs, the apparent heat capacity (which can be converted into relative weight) decreased with increasing total annealing time. The decrease in apparent heat capacity is explained by the progression of thermal oxidation. The nano-TG method was applied to determine the thermal oxidation kinetics of PP using the Avrami-Erofeev model. The non-isothermal TG curve calculated from the kinetic parameters of the nano-TG analysis was in good agreement with the experimental data obtained from the conventional TG measurements for the early stage of weight loss. The present method is applicable for the thermal degradation/oxidation analysis of microplastics in the environment or small impurity analysis of polymers.

The Role of Carbonized Layers for Fire Protection of Polymer Materials

The present work studies the processes occurring in pre-flame zone in the form of «candle-like flame» which is spread over the surface of epoxy polymer. As exemplified by epoxy polymer, it can be seen that the dominating mechanism of heat transfer from flame to pre-flame zone of carbonized polymers is a thermal conductivity by condensed phase (to phase). The mechanism of gasification processes in pre-flame zone is proposed. Gasification of the material in front of the flame edge is a controlling process, and when selecting flame retardants, it is necessary to register their ability to influence on kinetics and mechanism of gasification. The flame leading edge is bordered with the surface of polymer, which largely determines the nature of heat transfer in pre-flame region. Due to investigations of gas-phase composition at «candle-like» combustion of epoxy polymer it has been detected a considerable amount of oxygen (up to 10‒12%) near burning surface. Its presence facilitates the thermal oxidation of polymer, moreover the rate of thermal oxidation can significantly exceed the thermal decomposition rate of the polymer. The possibility to form the heat-insulating intumescent layer during decomposition of carbonizable polymers was used at development of flame retardant coatings ‒ complex multicomponent systems. Which in turns forms the intumescent carbonized layer with high porosity and low thermal conductivity, and protects based material or construction from premature heating up to critical temperatures.

Influence of free surface energy of polymers on formation of their interphase contact with oxyethylated isononylphenol

The interconnection of the surface energy characteristics of polymers in a wide range of acid-base constituents of the free surface energy and their adhesive interaction with adducts of ethylene oxide and isononylphenol was investigated. It was shown that the content of the polar groups in the polymer surface layer and the length of the oxyethylene chain additively influence the wetting ability and the work of adhesion. The peculiarities of the adhesive interaction of high pressure polyethylene with oxyethylated compounds depending on the thermal oxidation of polymer and the acidity parameters of the surface were revealed.

Metallocene ethylene-1-octene copolymers: Effect of extrusion conditions on thermal oxidation of polymers with different comonomer content

Metallocene ethylene-1-octene copolymers having different densities and comonomer content ranging from 11 to 36 wt% (m-LLDPE), and a Ziegler copolymer (z-LLDPE) containing the same level of short-chain branching (SCB) corresponding to one of the m-LLDPE polymers, were subjected to extrusion. The effects of temperature (210–285 °C) and multi-pass extrusions (up to five passes) on the rheological and structural characteristics of these polymers were investigated using melt index and capillary rheometry, along with spectroscopic characterisation of the evolution of various products by FTIR, 13C-NMR and colour measurements. The aim is to develop a better understanding of the effects of processing variables on the structure and thermal degradation of these polymers. Results from rheology show that both extrusion temperature and the amount of comonomer have a significant influence on the polymer melt thermo-oxidative behaviour. At low to intermediate processing temperatures, all m-LLDPE polymers exhibited similar behaviour with crosslinking reactions dominating their thermal oxidation. By contrast, at higher processing temperatures, the behaviour of the metallocene polymers changed depending on the level of comonomer content: higher SCB gave rise to predominantly chain scission reactions whereas polymers with lower level of SCB continued to be dominated by crosslinking. This temperature dependence was attributed to changes in the different evolution of carbonyl and unsaturated compounds including vinyl, vinylidene and trans-vinylene.

Temperature Limit for Fullerene C60 as an Antioxidant in the Thermal Oxidation of Polymers

Temperature Limit for Fullerene C₆₀ as an Antioxidant in the Thermal Oxidation of Polymers

Static manometric system for the quantitative measurement of gas absorption during thermal oxidation of polymers

It was shown that a static manometric system can be used for the measurement of the rate of oxygen absorption during thermal oxidation of polymers.

The formation and significance of polyconjugated systems in thermal and thermo-oxidative processes

The processes of formation of polyconjugatcd fragments during thermal oxidation of polymers and the reactions of low molecular compounds yielding polymers with an extended system of conjugation are considered. It is shown from the experimental data that the polyconjugated system (PCS) formed during thermal oxidation and thermolysis exerts initiating or activating action during the process. The cause of such properties of the PCS is the existence in macromolecules of stable biradicals capable of complex formation with diamagnetic molecules. in this complex the radical reactivity is enhanced due to an increased probability of ST transfer (effect of local activation). Initiation of hydroperoxide decomposition caused by the PCS explains the high synergetic action of mixtures of polyconjugated polymers formed during thermal oxidation or thermolysis of monomeric inhibitors (bisphenols, aromatic amines, etc.) and initial monomers not subjected to such treatment. It is shown that during thermolysis along with paramagnetic centres (PMC), the active radicals are formed due to the rupture of valence bonds. These a-radicals stabilized by a rigid matrix diminish the thermal-oxidative stability when molecular mobility is 'frozen'. The activity of a-radicals, under proper conditions, can suppress the inhibiting effect of stable PMC complexes and cause transition from oxidation to burning. The probability of purposeful regulation of PCS action is associated with the information about the PMC formation mechanism during the growth of polyconjugated chain. The author's attitude concerning the existence of paramagnetic branched chains resulting from local ic-bonds unpairing in PCS is considered. Due to this fact a paramagnetic avalanche is formed because of ST transition activation in a complex with other macromolecules by PMC formed during the preceding step. The advanced theory is in excellent agreement with known experimental data and may be useful for interpretation and prediction of the results of future investigations. By means of thermodynamic calculations it is easy to show that in many cases the propagation of a polyconjugated chain is the most probable process in the thermal and thermo-oxidative destruction of organic compounds1. The reason for this is connected with the decrease in internal energy for the transition from 'saturated' compounds to substances with a system of

Changes in the concentration of paramagnetic centres in polyconjugated compounds during inhibition of the thermal oxidation of polymers

Changes in the concentration of paramagnetic centres in polyconjugated compounds during inhibition of the thermal oxidation of polymers

Thermal oxidation of certain aromatic polyamides at high temperatures

1. The thermooxidative destruction of two samples of polyamides was investigated at temperatures of 325–500°C in air and in an atmosphere of oxygen. 2. The process of thermal oxidation of polymers does not differ significantly from their thermal decomposition. At relatively low temperatures, hydrolytic processes of decomposition dominate, while at high temperatures radical processes are dominant. 3. Oxygen is not an initiator of the thermooxidative destruction of aromatic polyamides.