Kinetics of thermal degradation in non-isothermal conditions of some phosphorus-containing polyesters and polyesterimides

Effects of Phosphorus and Boron Compounds on Thermal Stability and Flame Retardancy Properties of Epoxy Composites

While plastics are regarded as the most resourceful materials nowadays, ranging from countless utilities including protective or decorating coatings, to adhesives, packaging materials, electronic components, paintings, furniture, insulating composites, foams, building blocks and so on, their critical limitation is their advanced flammability, which in fire incidents can result in dramatic human fatalities and irreversible environmental damage. Herein, epoxy-based composites with improved flame-resistant characteristics have been prepared by incorporating two flame retardant additives into epoxy resin, namely 6-(hydroxy(phenyl)methyl)-6H-dibenzo[c,e][1,2]oxaphosphinine-6-oxide (PFR) and boric acid (H₃BO₃). The additional reaction of 9,10-dihydro-oxa-10-phosphophenanthrene-10-oxide (DOPO) to the carbonyl group of benzaldehyde yielded PFR, which was then used to prepare epoxy composites having a phosphorus content ranging from 1.5 to 4 wt%, while the boron content was 2 wt%. The structure, morphology, thermal stability and flammability of resulted epoxy composites were investigated by FTIR spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis, differential scanning calorimetry, and microscale combustion calorimetry (MCC). Thermogravimetric analysis indicated that the simultaneous incorporation of PFR and H₃BO₃ improved the thermal stability of the char residue at high temperatures. The surface morphology of the char residues, studied by SEM measurements, showed improved characteristics in the case of the samples containing both phosphorus and boron atoms. The MCC tests revealed a significant reduction in flammability as well as a significant decrease in heat release capacity for samples containing both PFR and H₃BO₃ compared to the neat epoxy thermoset.

Thermal Stability, Smoke Density, and Flame Retardance of Ecotype Bio-Based Flame Retardant Agricultural Waste Bagasse/Epoxy Composites

In the study, agricultural waste bagasse was used as a bio-based flame retardant for reducing the flammability of epoxy. Specifically, an interpenetrating network (IPN) was formed through a ring opening reaction between the hydroxyl functional group of bagasse and the epoxy group of triglycidyl isocyanurate (TGIC), forming Bagasse@TGIC. Next, 9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) was mixed with Bagasse@TGIC, inducing a reaction between the active hydrogen of DOPO and the epoxy group of TGIC, ultimately forming Bagasse@TGIC@DOPO with an IPN structure. Finally, the novel flame retardant was added to epoxy to create a composite. The integral procedural decomposition temperature (IPDT) of pure epoxy is 619 °C; after the introduction of the 30 wt% flame retardant, the IPDT of the resultant composite material increased to 799 °C, greatly increasing the thermal stability by 29%. After the addition of the Bagasse@TGIC@DOPO flame retardant, the limiting oxygen index increased from 21% for the pure epoxy to 29% for the composite, and the UL-94 rating improved from failing rating for the pure epoxy and V-0 rating for the composite. The Raman spectrum indicated that the addition of Bagasse@TGIC@DOPO IPN substantially increased the biochar yield during the burning process, increasing thermal stability. These results confirmed that the epoxy/Bagasse@TGIC@DOPO composite had substantial flame retarding effects.

Liquid crystalline hyperbranched polyesters with phosphorus functional groups

Liquid crystalline hyperbranched poly(aryl ester)s (A2B3) were prepared by polycondensation reaction of 2-(6-oxido-6H-dibenz<c,e><1,2>oxaphosphorin-6-yl)1,4-naphthalene diol with 1,3,5-benzenetricarbonyl trichloride, taken in two different molar ratios. The chemical structure of the newly synthesized hyperbranched polymers was confirmed by FTIR, 1H NMR, 13C NMR spectroscopy. The polymers exhibited high thermal stability with initial decomposition temperature above 410–435°C and char yield at 700°C higher than 40%. Combined differential scanning calorimetry, polarized optical microscopy and wide-angle X-ray diffraction measurements were carried out to closely examine their thermal behavior and phase transitions.

Synthesis, characterization and thermal degradation kinetics of azomethine-based halogen-free flame-retardant polyphosphonates

In this study, azomethine polyphosphonates were synthesized by solution polycondensation of phenylphosphonic dichloride with various azomethine diols such as [4-(4-hydroxy phenyl) iminomethyl] phenol, [(4-(4-hydroxy-3-methoxy phenyl) iminomethyl)] phenol and [4-(4-hydroxy-3-ethoxy phenyl) iminomethyl] phenol using triethylamine catalyst at ambient temperature. The structure of the synthesized polymers was confirmed by Fourier transform infrared and 1H-, 13C- and 31P- nuclear magnetic resonance spectroscopic techniques. Thermal properties of the polymers were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry under nitrogen atmosphere. The TGA data showed that the synthesized polyphosphonates produce high char yield at 600°C due to the presence of phosphorous atom in the polymer chain and hence have good flame-retardant properties. One of the synthesized polyphosphonate was blended with commercial diglycidyl ether of bisphenol-A (DGEBA) resin in various weight percentage and cured with commercial curing agent triethylene tetramine (TETA). The polyphosphonates-blended epoxy thermosets have tensile strength in the range of 5–41 MPa and the percentage of elongation at breaks was 4–18. It was found that the incorporation of polyphosphonates into epoxy thermoset decreased the tensile strength from 41 MPa to 5 MPa, whereas the elongation at break value increased with increase in the weight percentage of polyphosphonate. The influence of polyphosphonates on the flame retardancy of blended thermosets was examined by limiting oxygen index (LOI) and vertical burning (UL-94) tests and found that the polymer samples achieved an increased UL-94 rating and the LOI values were in the range of 24–26. Broido and Horowitz–Metzger methods have been used to study the thermal degradation kinetic parameters.

Synthesis and characterization of cardo-based phosphorous–containing flame-retardant aromatic polyesters

Phosphorous-containing cardo polyesters were synthesized by interfacial polycondensation of phenylphosphonic dichloride with various bisphenols using a phase-transfer catalyst at ambient temperature. The structure of the synthesized polymers was confirmed using Fourier transform infrared and proton, carbon 13, and phosphorous 31 nuclear magnetic resonance spectroscopic techniques. The thermal properties of the polymers were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry under nitrogen atmosphere. All the polyesters showed high thermal stability, the maximum decomposition temperature being in the range of 475–523°C. The TGA data showed that all the synthesized phosphorous-containing polyesters produce high char yield at 700°C due to the presence of phosphorous atom in the polymer chain and hence have good flame-retardant properties. The synthesized phosphorus-containing polyesters have tensile strength in the range of 38.2–48 MPa, and the percentage of elongation at breaks of 3.3–16.8. The flame retardancy of all synthesized polymers was investigated by limiting oxygen index (LOI) and vertical burning (UL-94) tests. The results showed that the synthesized polymers have excellent flame retardancy, that is, the polymer samples achieved an increased UL-94 rating and the LOI values were in the range of 28.5–34. Broido model has been used to study the thermal degradation kinetic parameters.

Environmentally friendly fire-resistant epoxy resins based on a new oligophosphonate with high flame retardant efficiency

New fire resistant epoxy resins were prepared. The kinetic processing of thermogravimetric data was performed using Friedman and Vyazovkin methods.

Synthetic investigation of glycine catalyzed triarylimidazole based organophosphorous heterocyclic functionalized vinyl polymer - A green approach

In the present investigation, an efficient and environmentally adopted synthesis of triaryl substituted imidazole in one-pot was reported. The multicomponent reaction between various aldehydes, benzil, benzoin, ammonium acetate and glycine under solvent free condition has been explained. Instead of using toxic reagents for the synthesis of heterocyclic compounds, Glycine has been selected as a green catalyst due to simple work-up procedure, shorter reaction time and high yield. The synthesized imidazole derivatives on further treatment with phosphorous oxychloride resulted in an organophosphorous containing N-heterocyclic compound (N-P) thus by altering acidic hydrogen of imidazole. Further, N-P was reacted with polyvinyl alcohol resulted into organophosphorous N-heterocyclic vinyl polymers. The synthesized vinyl polymers were characterized using, FTIR, NMR and Mass spectral studies. Results of the spectral studies were well supported the formation of the compounds. Thermal stability have also been studied using TGA.

Nonisothermal and isothermal oxidative degradation behavior of thermotropic liquid crystal polyesters containing kinked bisphenol AF and bisphenol A units

The polyester P–bisphenol AF 2.5 (BPAF 2.5) and P-bisphenol A 2.5 (BPA 2.5) with low melting temperature and high glass transition temperature can be obtained by introducing 2.5 mol% BPAF/BPA and terephthalic acid (TA) units respectively into the molecular chain of poly(oxybenzoate- co-oxynaphthoate) (P-HBA70). In this study, the nonisothermal and isothermal oxidative degradation behavior of polyester P-BPA2.5 and P-BPAF2.5 were investigated comparatively with parent polyester P-HBA70 by thermogravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy measurements. The introduction of BPAF/BPA units into the molecular chain of P-HBA70 strongly influenced the degradation behavior of polyesters. Four multiple heating rate methods including Kissinger, Kim–Park, Flynn–Wall–Ozawa, and Friedman methods were applied to evaluate the dynamic thermal stability successfully. The following order of the activation energy values: P-BPAF2.5 > P-HBA70 > P-BPA2.5 can be found for the three samples. However, from the results obtained by the standard isoconversional method, the P-BPA2.5 showed a better thermal stability as compared to P-BPAF2.5 under isothermal atmosphere.

Study of the thermal decomposition of some azopolyimides

The thermal decomposition of some polyimides containing pendent azobenzene groups was investigated with dynamic thermogravimetric analysis. Thermal degradation of azopolyimides took place in two or three steps. Traditional nonisothermal experiments involved linearizing an equation in some manner and fitting the resulting straight line to obtain the activation energy ( Ea). The variation in activation energy with conversion degree of these polymers, obtained from two different kinetic methods, such as Flynn–Wall–Ozawa and Friedman, were compared and discussed.

New Polyesterimides Containing Bulky, Cyclic Phosphorus Groups

A new phosphorus-containing monomer, bis( N-hydroxyethyl-phthalimidyl)-bis(9,10-dihydro-9-oxa-10-oxide-10-phosphaphenanthrene-10-yl)methane, that contains preformed imide rings and flexible linking groups was synthesized. This compound was used to synthesize new phosphorus-containing polyesterimides by solution polycondensation with various aromatic diacide chlorides such as terephthaloyl chloride, terephthaloyl-bis-(4-oxybenzoylchloride), 4-chloroformyl- N( p-chloroformylphenyl)-phthalimide and 2,2-bis(4-chloroformyl- N-phthalimidyl)-diphenylmethane. The rates of the polycondensation reactions were calculated from kinetic investigations. The polymers were readily soluble in polar organic solvents, such as N-methylpyrrolidone, N, N-dimethylacetamide and N, N-dimethylformamide. The polymers were analytically, spectrally and thermally characterized.

Thermal Degradation Kinetics of some Aromatic Poly(1,3,4-oxadiazole-ether)s

Poly(1,3,4-oxadiazole-ether)s containing isopropylidene, hexafluoroisopropylidene, cyclohexylidene, fluorene, phthalide or phenylquinoxaline groups have been prepared by nucleophilic substitution polymerization technique of 2,5-bis( p-fluorophenyl)-1,3,4-oxadiazole with various aromatic bisphenols. The thermal decomposition behavior of the polymers was studied using thermogravimetric analysis in air, at several heating rates: 6, 10 and 14° C min . The polymers showed high thermo-oxidative stability with decomposition temperature corresponding to 5% weight loss above 380°C. The kinetic processing of data was carried out using the Coats—Redfern, Reich—Levi, Flyn—Wall and Kissinger methods.