Thermo-oxidative Stability Of Polypropylene Research Articles

Synthesis of Nanoplatelet Zinc Borate and its Combination with Expandable Graphite and Red Phosphorus as Flame Retardants for Polypropylene

The zinc borate nanoparticles (2ZnO.3B2O3.3H2O) were successfully prepared by precipitation reaction in aqueous solutions of borax and zinc sulfate using oleic acid as a surfactant. The structural, morphological characteristics and the wettability of the particle surface were studied through Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and the contact angle. The hydrophobic zinc borate (n-ZB) had nanoplatelet morphology with a diameter of 1.0 - 1.5 µm and thickness of about 90 nm. Nano zinc borate showed a synergistic influence with expandable graphite (EG) and red phosphorus (RP) on the flame retardant properties and thermo-oxidative stability of polypropylene (PP). The nanocomposite 7n-ZB/7RP/7EG/PP achieved the V-1 UL94 verticle burning test with a limited oxygen index of 23.7% and the char yield of 14.67 wt.% at 900 oC. Furthermore, the fire retardant performance and the mechanical properties of the nanocomposites loading ZB nanoparticles were improved compared with the composites employing commercial ZB microparticles.

Novel octa-substituted metal (II) phthalocyanines bearing 2,6-di-tert-buthylphenol groups: Synthesis, characterization, electronic properties, aggregation behavior and their antioxidant activities as stabilizer for polypropylene and high density polyethylene

Novel metallophthalocyanines [M: Co (II), Cu (II), Zn (II), Mn (II)] bearing eight peripheral 2,6-di-tert-buthylphenol groups were successfully synthesized. The new products were studied by FTIR, 1H NMR, MADLI-TOF, UV/VIS spectral data and thermogravimetric analysis. The aggregation behavior of the new phthalocyanines was investigated in different solvents and concentrations. In addition, the antioxidant activities were analyzed through radical scavenging of 1,1-diphenyl-2-picrylhydrazyl (DPPH). All the new compounds had radical scavenging activity higher than polymer's commercial antioxidant and the highest DPPH activity was obtained from phthalocyanine copper (II). Moreover, the thermooxidative stability of polypropylene (PP) and high density polyethylene (HDPE) with the new antioxidants were assessed by the measurements of the oxidation induction time (OIT), differential scanning calorimetry (DSC) test and melt flow index (MFI) analysis. The results showed that the newly synthesized phthalocyanine complexes could effectively inhibit the oxidation degradation of PP and HDPE.

Thermooxidative stability of polypropylene/TiO2 and polypropylene/layered silicate nanocomposites

Thermooxidative stability of polypropylene (PP), PP/TiO2 and PP/Cloisite 10A nanocomposites was studied using non-isothermal DTA measurements. The effect of various concentrations of both nanofillers on the stability of pristine PP was evaluated. Moreover, the influence of additional processing cycles on the stability of all samples was investigated. For the treatment of the experimental results, our method for the evaluation of the induction periods of thermal oxidation using non-Arrhenian temperature functions was employed. Values of the induction periods were taken as a measure of the samples stability. The results obtained clearly demonstrate that both TiO2 and Cloisite 10A nanoparticles accelerate thermooxidative degradation of PP. Stability of nanocomposites decreases drastically in comparison with pristine PP, especially at lower concentrations of both nanofillers. The lifetime of all PP samples decreases with additional processing cycles. The steepest decrease is observed after first and second additional passes through the extruder, and then, the stability remains almost constant up to five passes.

Photo- and thermo-oxidative aging of polypropylene filled with surface modified fumed nanosilica

Fumed nanosilica (FS) was treated separately by different silane coupling agents, including n-dodecyl-trimethoxyl silane (DTMS), aminoethylaminopropyl-trimethoxyl silane (AEAPS), aminopropyl-trimethoxyl silane (APS) and methacryloxypropyl-trimethoxyl silane (MAPS). Their influences on photo- and thermo-oxidative aging of polypropylene were evaluated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The photoaging of polypropylene was accelerated by the MAPS-modified FS but delayed by the neat FS and other modified FS. On the other hand, the thermal and thermo-oxidative stability of polypropylene were improved with the incorporation of the nanoparticles, independent of the modification. The AEAPS-modified FS and the APS-modified FS revealed simultaneously noticeable enhancement in both photo-stability and thermo-oxidative stability of polypropylene. The possible mechanism was discussed.

Cork extractives exhibit thermo-oxidative protection properties in polypropylene–cork composites and as direct additives for polypropylene

The thermo-oxidative stability of polypropylene (PP) in composites containing 15 wt.% of cork and the performance of selected cork extracts as stabilizing additives for PP was evaluated by Oxidation Induction Time (OIT) and by Oxidation Onset Temperature (OOT). The results showed that cork increases the OIT of PP in the composite and it was identified that the cork extractives fraction is responsible for such behavior. Selected cork extracts with high antioxidant capacity (determined by dpph radical scavenging and oxygen reactive absorbance capacity assays) were compounded by extrusion with PP in 0.5 and 1.5 wt.%. It was found that the ethanol extract is the most effective as thermo-oxidative stabilizer for PP. At the loading level of 1.5%, the OIT increases from 3.8 (neat PP) to 29.7 min at 200 °C and from 1.2 (neat PP) to 9.0 min at 220 °C. The OOT also increases from 216 °C (neat PP) to 247 °C. Mechanical tests, performed on PP loaded with the cork extracts, showed that the presence of these extracts has no significant effect on the polymer mechanical performance. The results demonstrate the suitability of cork as a source of thermo-oxidative stabilizing additives for the formulation of polyolefins, and enable the exploitation of new routes of cork valorization.

Synthesis of 3,5-ditert-butyl-4-hydroxybenzoates and their thermal antioxidation behavior for polypropylene

Butyl 3,5-ditert-butyl-4-hydroxybenzoate (BB), octyl 3,5-ditert-butyl-4-hydroxybenzoate (OB), and dodecyl 3,5-ditert-butyl-4-hydroxybenzoate (DB) were synthesized and characterized, and their performance as antioxidant for polypropylene (PP) were also investigated. The thermooxidative stability of PP with different antioxidants were assessed by the measurements of long-term accelerated aging, differential scanning calorimetery, and thermogravimetric analysis. The results showed that 3,5-ditert-butyl-4-hydroxybenzoates could effectively inhibit the oxidation degradation of PP. And it was also found that the antioxidant efficiency of BB, OB, and DB for PP was in the order of DB > OB > BB.

Study of CaCO 3 filled polypropylene composite with long use life time

The ageing properties of CaCO 3 filled polypropylene (PP) composite have been studied using light, weathering and oven ageing. The results show that industrial grade CaCO 3 can slightly inhibit the thermo-oxidation of PP, while the effect of CaCO 3 on the photo-oxidation of PP is very small. The photo-oxidation and thermo-oxidative stability of PP can be improved by adding Hindered Amine Light Stabilizer (HALS) and phenol antioxidant. The effectiveness of light stabilizer or antioxidant is considerably decreased by adding CaCO 3. The effectiveness of light stabilizers is in the order 770 > 540 > 531 > PDS while the effectiveness of antioxidants is in the order 1010 > 264. The effects of industrial CaCO 3 on the thermo-oxidation of PP and on the effectiveness of stabilizer have been discussed and the compositions of filled PP with long use life time have been proposed.

Advances in the stabilization of polyolefins

The current status of polyolefin stabilization is reviewed with respect to processing, long term heat aging (LTHA) and UV stability. The main trends in practical stabilization are discussed in detail. For LTHA of polyolefins the latest development consists in an increasing use of polymeric or high molecular weight HALS. Thermooxidative stability of polypropylene, high density polyethylene, low density polyethylene and linear low density polyethylene can be increased considerably by addition of high molecular weight HALS to the base stabilization. This is shown for PP tapes and PP multifilaments, LDPE and LLDPE films as well as PP and HDPE thick sections. The UV stability of polyolefins achieved with low molecular weight HALS or high molecular weight HALS can be improved significantly in numerous applications by the use of combinations of low molecular weight HALS with high molecular weight HALS. This is exemplified with data for PP films, PP tapes, talc filled PP plaques and PP/EPR bumpers.

Thermo-oxidative stability of polypropylene in the presence of substituted 3-anilino-1,5-diphenyl pyrazoles

The antioxidant efficiencies of a series of 3-anilino-1,5-diphenyl pyrazoles on the thermo-oxidation of isotactic polypropylene have been studied using thermogravimetry, differential scanning calorimetry and chemiluminescence. The efficiencies depend upon the nature of the substituents, their position on the phenyl rings and their distance from the ▪ group which is the primary reaction centre. Other factors are the planarity of the molecule, the degree of conjugation and the additional antioxidant efficiency of transformation products.

Thermooxidative stability of polypropylene under the simultaneous action of high pressure and shear deformation

The thermooxidative stability of PP is enhanced after the joint action of high pressure and shear deformation. The higher the pressure, the more marked is the observed effect. By the introduction of a reactive monomer we obtained a longer induction period and a lower rate of oxidation, while the introduction of amorphous SiO 2 resulted in a lengthening of the induction period with no change in the rate of oxidation.

Influence of sulphur compounds on the inhibition of the thermo-oxidation of polypropylene

This is a report on the thermo-oxidative stability of polypropylene, stabilized by inhibitors of the bisalkylphenol types and by their mixtures with sulphur compounds. The hindered phenols used were:— 4,4′-butylidene- bis (3-methyl-6- tert-butylpenhol) and 2,2′-methylidene- bis (4-methyl-6- tert-butylphenol); the following sulphur compounds in mixtures with phenolic inhibitors were used: di- n-dodecylsulphide, di- n-dodecylsulphoxide and di- n-dodecyl ester of thio-di-propionic acid. It was proved that the effect of the synergistic component from the group of sulphur compounds depends on the mechanism of the primary reactions of the phenolic inhibitors in the system. The synergistic effects were exhibited by mixtures of 2,2′-methylidene- bis (4-methyl-6- tert-butylphenol) with di- n-dodecyl ester of thio-di-propionic acid and of 4,4′-butylidene-bis (3-methyl-6- tert-butyl-phenol) with di- n-dodecylsulphide.

Thermooxidative stability of polypropylene with regard to the concentration of hydroperoxides in the presence of phenolic stabilizer

The inhibited oxidation of atactic polypropylene containing different initial concentrations of hydroperoxidic groups has been studied at 120°C and in the temperature range 160° to 170°C. The mathematical expressions for the dependence of the length of the induction period on concentrations of phenolic stabilizer and hydroperoxidic groups have been derived. It follows from the kinetic analysis that the derived equation for 120°C is valid for the concentration range of stabilizer at which the rates of radical termination by stabilizer and by recombination are of the same order. The expression valid for the temperature range 160° to 170°C has been found to be identical with Shlypanikov's equation derived for the temperatures 180° to 210°C. The critical antioxidant concentration and the length of the induction period are both functions of the initial concentration of hydroperoxidic groups. The activation energy of the direct oxidation of antioxidant 2246 has been determined.