Melt Stability Research Articles

Influence of a Phenethyl-Bridged DOPO Derivative on the Flame Retardancy, Thermal Properties, and Mechanical Properties of Poly(lactic acid)

A phenethyl-bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide derivative (DiDOPO) was synthesized and characterized. The effects of DiDOPO on the fire resistance, thermal performances, and mechanical performances of poly(lactic acid) (PLA) were examined. PLA/10 wt % DiDOPO obtained the V-0 rating (UL-94) at thicknesses of 3.2 and 1.6 mm with an increased limiting oxygen index value of 27.1%. The incorporation of DiDOPO evidently prolonged the ignition and decreased the peak heat release of PLA. Moreover, PLA/DiDOPO had higher thermal stability than neat PLA especially under the air condition. The added DiDOPO could obviously change the crystallization properties of PLA. In addition, the flexural strength of PLA composites increased by 15.8% with 10 wt % loading of DiDOPO. Rheological analysis indicated that DiDOPO suppressed the melt dripping of PLA by enhancing the melt stability, which was caused by a continuous morphology of DiDOPO in PLA. Overall, DiDOPO is a good flame retardant with a poten...

The influence of substrate and atmosphere on the properties of FeSiB(Cu,Nb) alloy melts

The surface tensions and contact angles of Fe78Si9B13 and Fe73.5Cu1Nb3Si13.5B9 alloy melts were studied as a function of temperature in various atmospheres (vacuum, Ar and N2 gas) and on different substrates (SiC, Al2O3 and BN). It is indicated that Si3N4, NbN, Fe2AlB and B13C2 are generated as new phases at the interface between the melt and substrate, and reactive wetting behaviour exists during the heating process. The surface tensions of two alloy melts on BN substrate both firstly decrease and then increase along with increasing temperature, leading to V-shaped surface tension versus temperature, which results from atomic diffusion effects in the surface layer during the oxidation of BN and formation of C-rich layer. Comparably, the surface tensions on Al2O3 and SiC substrates decrease with increasing temperature throughout the entire temperature range. Among three substrates, BN exhibits the mildest wetting behaviour. The vacuum environment has the strongest protective effect on melt stability among the tested atmospheres. These findings enrich our knowledge about the effects of the substrate and atmosphere on Fe-based alloy melts at a high temperature, and provide theoretical reference for designing jet nozzles in melt-spinning techniques.

Melt stabilization of polyethylene with dihydromyricetin, a natural antioxidant

Experiments have been carried out to compare the stabilization effect of two flavonoid type natural antioxidants, dihydromyricetin (DHM) and quercetin (Q) in polyethylene (PE). Additive concentrations changed between 0 and 500 ppm in several steps and 1000 ppm Sandostab PEPQ phosphorus containing secondary stabilizer was also added to each compound. Both antioxidants are very efficient stabilizers for PE, sufficient melt stability was achieved already at 50 ppm DHM content. At small concentrations dihydromyricetin proved to be more efficient melt stabilizer and it protected the secondary antioxidant better than quercetin. In spite of its better efficiency in melt stabilization, polymers containing DHM had the same residual stability as those prepared with quercetin. Accordingly, the larger efficiency does not result from the larger number of active phenolic hydroxyls in the molecule, but from interactions with the phosphorous secondary stabilizer that is stronger or at least different for DHM than quercetin. In spite that DHM is a white powder, it gave the polymer a brownish color which became deeper with increasing number of extrusions and additive content. Nevertheless, both natural antioxidants can be used efficiently for the stabilization of polymers in applications in which color is of secondary importance.

Thermal stability of melt grown Tl-doped PbTeSe material for thermoelectric applications

Although the thermoelectric performance of PbTe-based materials, processed by hot-pressing, has recently been improved, there are concerns about its thermal stability. On the other hand, during the process of melt crystal growth the material is formed in a quasi-equilibrium condition, which results in homogeneous solid structure in a lower-energy state and, consequently, more thermally stable and mechanically robust. To test the thermal stability of the melt-grown crystal, a Tl-doped PbTe0.85 Se0.15 ingot has been grown from the melt by directional solidification. Four adjacent disc-shape samples were sliced perpendicular to the growth axis from the grown boule. The thermoelectric characterizations together with microstructure examination and mechanical hardness measurements were performed on each of the three as-grown samples as well as on the fourth sample after it has been annealed at 455°C for 570h. The characterization results, showing that the annealing has essentially no effects on the thermoelectric properties, metallurgical microstructure as well as mechanical hardness of the annealed sample, have demonstrated that structurally homogeneous materials processed by melt growth are more suitable than those processed by other methods, such as hot press or quench-annealing, for long-term thermoelectric applications at elevated temperatures.

The influence of processing aids on the melt stability and mobility of poly(arylene sulfide sulfone)

The phosphorous antioxidant bis[2,4-bis(1-methyl-1-phenylethyl)phenyl] pentaerythritol diphosphite (s-9228), hindered phenol antioxidant N, N′-hexane-1,6-diylbis-[3,5-di-tert-butyl-4-hydroxyphenylpropionamide] (1098), and zinc acetate (ZnAc) were chosen as processing aids to improve the melt stability and mobility of poly(arylene sulfide sulfone) (PASS). Different contents and components of the processing aids were discussed. The capillary rheometer test demonstrated that 3 wt% ZnAc showed better effect with the change of the shear rates. In contrast, the parallel-plate rheometer test proved that the complex antioxidant, including 0.8 wt% s-9228 and 1.6 wt% 1098, showed better effect with the change of temperature. Both the capillary rheometer and parallel-plate rheometer test showed that the compounding aid consisting of 0.8 wt% s-9228, 1.6 wt% 1098, and 3 wt% ZnAc showed the best effect with the dramatically improved melt stability and mobility. Also, PASS could be processed successfully by extruding and through an injection machine with the help of the compounding aid. Meanwhile, the effects of the applied processing aids on melt complex viscosity and modulus were also discussed.

Influence of Ag and Co additions on glass-forming ability, thermal and mechanical properties of Cu–Zr–Al bulk metallic glasses

In this study, the effect different amounts of Ag and Co have on thermal stability, phase formation and mechanical properties of the glass-forming alloys (Cu0.5Zr0.5)95−x−yAl5AgxCoy (2≤x≤5 and 0≤y≤2) and Cu47.5−yZr47.5Al5Coy (0≤y≤2) was investigated, respectively. The addition of Ag increases the glass-forming ability (GFA) of the alloys by enhancing the stability of the undercooled melt and by simultaneously reducing the stability of the B2 CuZr high-temperature phase. Co instead, has the opposite effect. It leads to an increased thermal stability of the B2 phase, as well as a decreased stability of the undercooled melt and, consequently, lowers the GFA of the alloys. Moreover, a metastable big cube phase precipitates in some alloys stabilized by oxygen, which is introduced during casting. There is a strong interdependence between the phase formation and the tendency of the present alloys to vitrify. This correlation can be captured by the K-parameter (Song et al. 2011 [1]) calculated from the respective transformation temperatures. The plastic strain of the present ternary, quaternary and quinary alloys reflects the GFA as well: the higher the tendency to form a glass, the smaller the plastic strain. Once B2 crystals precipitate in the glass, the plasticity is enhanced significantly.

New genre of antioxidants from renewable natural resources: Synthesis and characterisation of rosemary plant-derived antioxidants and their performance in polyolefins

Several ester derivatives of rosmarinic acid (rosmarinates) were synthesised, characterised (1D and 2D NMR, UV and FTIR spectroscopy) and tested for their potential use as antioxidants derived from a renewable natural resource. The intrinsic free radical scavenging activity of the rosmarinates was assessed, initially using a modified DPPH (2, 2-diphenyl-1-picrylhydrazyl radical) method, and found to be higher than that of commercial synthetic hindered phenol antioxidants Irganox 1076 and Irganox 1010. The thermal stabilising performance of the rosmarinates in polyethylene (PE) and polypropylene (PP) was subsequently examined and compared to that of samples prepared similarly but in the presence of Irganox 1076 (in PE) and Irganox 1010 (in PP) which are typically used for polyolefin stabilisation in industrial practice. The melt stability and the long-term thermo-oxidative stability (LTTS) of processed polymers containing the antioxidants were assessed by measuring the melt flow index (MFI), melt viscosity, oxidation induction time (OIT) and long-term (accelerated) thermal ageing performance. The results show that both the melt and the thermo-oxidative stabilisation afforded by the rosmarinates, and in particular the stearyl derivative, in both PE and PP, are superior to those of Irganox 1076 and Irganox 1010, hence their potential as effective sustainable bio-based antioxidants for polymers.The rosmarinic acid used for the synthesis of the rosmarinates esters in this study was obtained from commercial rosemary extracts (AquaROX80). Furthermore, a large number of different strains of UK-grown rosemary plants (Rosmarinum officinalis) were also extracted and analysed in order to examine their antioxidant content. It was found that the carnosic and the rosmarinic acids, and to a much lesser extent the carnosol, constituted the main antioxidant components of the UK-plants, with the two acids being present at a ratio of 3:1, respectively.

Influence of a novel organo-silylated clay on the morphology, thermal and burning behavior of low density polyethylene composites

Abstract The functionalization of a natural sodium montmorillonite (MMT) with (3-glycidyloxypropyl)trimethoxysilane by a silylation procedure is presented, and its use as nanofiller in the melt compounding of low density polyethylene (LDPE) nanocomposites. In particular, the effects on the thermal stability and flame retardant properties of melt compounded LDPE nanocomposites are analyzed, with and without magnesium hydroxide (MH) as an additional conventional flame retardant. The purpose was to investigate possible synergistic effects between the two inorganic fillers on fire behavior. The obtained organosilylated clay showed higher interlayer spacing than the original MMT and good thermal stability, higher than that of many commercial organoclays modified with alkylammonium salts. Its addition to LDPE allowed the production of hybrids with nanoscale dispersion of the filler, as demonstrated by X-ray diffraction. The simultaneous presence of MH, which strongly interacts with the nanoclay, hindered intercalation of the polymer chains between the clay galleries and clay layer exfoliation within the LDPE resin. The investigation of the thermal and burning behavior of the LDPE nanocomposites indicated that the organosilylated clay alone shows only a limited residual protection layer effect. In combination with MH the nanocomposites have a small adverse effect on the reaction to small flame as measured by the oxygen index and UL 94 testing, and, surprisingly, no effect on the peak heat release rate in the cone calorimeter. The quality of the fire residue was lacking on the microscopic scale. The ternary LDPE/MH/organoclay systems investigated did not open the door to reducing MH content in halogen-free flame retardant LDPE yet, but demand further research.

Macroscopic Behavior of Kraft Lignin Fractions: Melt Stability Considerations for Lignin–Polyethylene Blends

Questions that pertain to the behavior of softwood kraft lignin fractions as opposed to the whole lignin still prevail. In an effort to further understand such effects at a macroscopic level, we have examined the issue of melt stability of polyethylene (PE) in blends with fractionated and unfractionated softwood kraft lignin. While methylation of the phenolic OH groups significantly stabilizes any lignin/PE melt, more in depth data demonstrate that when separate, acetone soluble (ASKL) and acetone insoluble (AIKL) kraft lignin fractions behave completely differently than the original unfractionated material. The low molecular weight methylated ASKL offers unexpected plasticizing action to PE melts, possibly as a consequence of its low molecular weight and spherical configuration. The higher molecular weight AIKL offers relatively stable PE melts, possibly manifesting its rigid nature and higher glass transition temperature likely occurring due to π stacking operating among its aromatic rings. Mixing these...

Impact of polymer type on bioperformance and physical stability of hot melt extruded formulations of a poorly water soluble drug

Amorphous solid dispersion formulations have been widely used to enhance bioavailability of poorly soluble drugs. In these formulations, polymer is included to physically stabilize the amorphous drug by dispersing it in the polymeric carrier and thus forming a solid solution. The polymer can also maintain supersaturation and promote speciation during dissolution, thus enabling better absorption as compared to crystalline drug substance. In this paper, we report the use of hot melt extrusion (HME) to develop amorphous formulations of a poorly soluble compound (FaSSIF solubility=1μg/mL). The poor solubility of the compound and high dose (300mg) necessitated the use of amorphous formulation to achieve adequate bioperformance. The effect of using three different polymers (HPMCAS-HF, HPMCAS-LF and copovidone), on the dissolution, physical stability, and bioperformance of the formulations was demonstrated. In this particular case, HPMCAS-HF containing HME provided the highest bioavailability and also had better physical stability as compared to extrudates using HPMCAS-LF and copovidone. The data demonstrated that the polymer type can have significant impact on the formulation bioperformance and physical stability. Thus a thorough understanding of the polymer choice is imperative when designing an amorphous solid dispersion formulation, such that the formulation provides robust bioperformance and has adequate shelf life.

Acid-insoluble lignin and holocellulose from a lignocellulosic biowaste: Bio-fillers in poly(3-hydroxybutyrate)

This paper deals with the valorization of a lignocellulosic biomass (LC), biowaste from the second generation bioethanol production process. LC was processed in order to isolate its main components: holocellulose (HC) and acid-insoluble lignin (IL). To obtain a biomass free of organic extractives (TE) and low molecular weight polar compounds (W), LC was also subjected to solvent extraction with toluene/ethanol and water. IL, HC and LC were characterized by SEM, FTIR and 13C MAS-NMR. The morphological and structural analysis evidenced successful separation of the two main fractions of the lignocellulosic biomass.LC and its derivatives were used as fillers in poly(3-hydroxybutyrate) (PHB). The blends were characterized through rotational rheometry and DSC. Moreover, the samples were also thermally treated at 190°C, and the effects of the thermal processing on the matrix molecular weight was evaluated by GPC.The addition of IL to PHB affected its rheological properties, significantly enhancing melt stability due to the formation of a percolated filler network within the matrix. Furthermore, SEM analysis demonstrated homogeneous dispersion of the filler and good interfacial adhesion with the matrix. LC and TE acted as pro-degrading agents toward PHB matrix causing a decrease in molecular weight of the polymer during the thermal treatment. The DSC analysis showed that LC, HC, W and TE promoted the polymer melt crystallization, potentially enabling to control physical aging of PHB.To sum up, this study provides an insight on the effect of a lignocellulosic biowaste and its derivatives on the properties of a naturally occurring, biodegradable polyester.

Carbon-saturated monosulfide melting in the shallow mantle: solubility and effect on solidus

We present high-pressure experiments from 0.8 to 7.95 GPa to determine the effect of carbon on the solidus of mantle monosulfide. The graphite-saturated solidus of monosulfide (Fe0.69Ni0.23Cu0.01S1.00) is described by a Simon and Glatzel (Z Anorg Allg Chem 178:309–316, 1929) equation T (°C) = 969.0[P (GPa)/5.92 + 1]0.39 (1 ≤ P ≤ 8) and is ~80 ± 25 °C below the melting temperature found for carbon-free conditions. A series of comparison experiments using different capsule configurations and preparations document that the observed solidus-lowering is owing to graphite saturation and not an artifact of different capsules or hydrogen contamination. Concentrations of carbon in quenched graphite-saturated monosulfide melt measured by electron microprobe are 0.1–0.3 wt% in monosulfide melt and below the detection limit (<0.2 wt%) in crystalline monosulfide solid solution. Although there is only a small amount of carbon dissolved in monosulfide melts, the substantial effect on monosulfide solidus temperature means that the carbon-saturated monosulfide (Fe0.69Ni0.23Cu0.01S1.00) solidus intersects continental mantle geotherms inferred from diamond inclusion geobarometry at 6–7 GPa (~200 km), whereas carbon-free monosulfide (Fe0.69Ni0.23Cu0.01S1.00) solidus does not. The composition investigated (Fe0.69Ni0.23Cu0.01S1.00) has a comparatively low metal/sulfur (M/S) ratio and low Ni/(Fe + Ni), but sulfides with higher (M/S) and with greater Ni/(Fe + Ni) should melt at lower temperatures and these should have a broader melt stability field in the diamond formation environment and in the continental lithosphere. Low carbon solubility in monosulfide melt excludes the possibility that diamonds are crystallized from sulfide melt. Although monosulfide melt can store no more than 2 ppm C in a bulk mantle with 225 ppm S, melts with higher M/S could be a primary host of carbon in the deeper part of the upper mantle. For example, the storage capacity of C in sulfide melts in the deep upper mantle (~400 km) for a depleted mantle domain (MORB source, 120 ± 30 ppm S) is estimated to be \(57 \pm_{30}^{63}\) ppm, and so all the C could be in a sulfide melt. In an enriched (OIB source, 225 ± 25 ppm S) mantle domain, the C stored in sulfide melt in the deep upper mantle is estimated to be \(86 \pm_{44}^{92}\) ppm, which would amount to about half the available carbon.

Structure and density of basaltic melts at mantle conditions from first-principles simulations.

The origin and stability of deep-mantle melts, and the magmatic processes at different times of Earth's history are controlled by the physical properties of constituent silicate liquids. Here we report density functional theory-based simulations of model basalt, hydrous model basalt and near-MORB to assess the effects of iron and water on the melt structure and density, respectively. Our results suggest that as pressure increases, all types of coordination between major cations and anions strongly increase, and the water speciation changes from isolated species to extended forms. These structural changes are responsible for rapid initial melt densification on compression thereby making these basaltic melts possibly buoyantly stable at one or more depths. Our finding that the melt-water system is ideal (nearly zero volume of mixing) and miscible (negative enthalpy of mixing) over most of the mantle conditions strengthens the idea of potential water enrichment of deep-mantle melts and early magma ocean.

Rapid Stereocomplexation between Enantiomeric Comb-Shaped Cellulose-g-poly(L-lactide) Nanohybrids and Poly(D-lactide) from the Melt.

In this work we report the in situ preparation of fully biobased stereocomplex poly(lactide) (SC-PLA) nanocomposites grafted onto nanocrystalline cellulose (NCC). The stereocomplexation rate by compounding high-molar-mass poly(D-lactide) (PDLA) with comb-like NCC grafted poly(L-lactide) is rather high in comparison with mixtures of PDLA and PLLA. The rapid stereocomplexation was evidenced by a high stereocomplexation temperature (Tc-sc = 145 °C) and a high SC crystallinity (Xc-sc = 38%) upon fast cooling (50 °C/min) from the melt (250 °C for 2 min), which are higher than currently reported values. Moreover, the half-life crystallization time (175-190 °C) of the SC-PLA was shortened by 84-92% in comparison with the PDLA/PLLA blends. The high(er) stereocomplexation rate and the melt stability of the SC in the nanocomposites were ascribed to the nucleation effect of the chemically bonded NCC and the "memory effect" of molecular pairs in the stereocomplex melt because of the confined freedom of the grafted PLLA chains.

Hard Magnetic Properties and Thermal Stability for TbCu&lt;sub&gt;7&lt;/sub&gt;-Type SmCo&lt;sub&gt;6.4&lt;/sub&gt;Si&lt;sub&gt;0.3&lt;/sub&gt;Zr&lt;sub&gt;0.3&lt;/sub&gt; Alloys With Sm Substituted by Various Rare-Earth Elements

The magnetic properties and thermal stability of melt spun SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6.4</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> ribbons with various rare-earth (RE) elements substituted for Sm have been investigated. It is verified that the properties’ combination of SmCo <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> -based ribbons can be modified by selected RE substitution. The light RE Ce is beneficial for enhancing the saturation magnetization and the remanence, while the coercivity and thermal stability can be significantly improved by heavy REs Gd, Ho, and Er substitutions. The highest room-temperature coercivity of 1467 kA/m was achieved in the Sm <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> Gd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6.4</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> ribbon. For the temperature range of 27 °C–200 °C, Gd is the best element for enhancing the thermal stability, and the optimal temperature coefficients <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> are −0.032%/°C and −0.269%/°C, respectively. For the range of 27 °C–400 °C, Ho is the best element to improve the thermal stability, and the values of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula> are −0.064%/°C and −0.19%/°C, respectively.

Impact of fullerenes on the thermal stability of melt processed polystyrene and poly(methyl methacrylate) composites

The impact of the two fullerenes C60 and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) on the thermal and thermo-oxidative stability of the corresponding melt processed composites with the two polymers polystyrene (PS) and poly(methyl methacrylate) (PMMA), was studied using both dynamic and isothermal thermogravimetric analysis (TGA). For each polymer, three different composites with C60 loadings of 1.0 wt% and 3.0 wt% and PCBM loadings of 1.0 wt% were considered. The aim of this work was to compare the stabilization effect of both fullerenes on PS and PMMA. The results obtained show unequivocally that, although PCBM has lower thermal and thermo-oxidative stability than C60, the PS-PCBM and PMMA-PCBM composites have higher thermal and thermo-oxidative stability than the corresponding PS-C60 and PMMA-C60 composites. These results corroborate our previous reports, on showing that PCBM is better than C60 at improving the thermal and thermo-oxidative stability of polymers which degrade through radical degradation mechanisms.

Effect of rare earth additions on microstructure, thermal stability and crystallization behavior of melt spun Fe80.65Cu1.35Si2B14RE2 (RE=Y, Gd, Tb and Dy) soft magnetic alloys

The influences of RE alloying additions (Y, Gd, Tb and Dy) on the microstructure, thermal stability and crystallization behavior of melt spun Fe80.65Cu1.35Si2B14RE2 alloys have been systematically investigated. Substituting 2at% iron atoms by rare earth elements significantly improve the amorphous forming ability and thermal stability of the alloys. The primary crystallization temperatures are increased for at least 55°C. The crystallization behavior is dramatically changed with a steady existence of metastable Fe3B phase in the second stage of crystallization during the annealing process. For Fe80.65Cu1.35Si2B14Gd2 alloy, the Fe3B phase can be stably exist even the temperature rise up to 600°C. The addition of Y is found to be beneficial for the soft magnetic application of the alloy.

Melt processed polyethylene/fullerene nanocomposites with highly improved thermo-oxidative stability

The thermo-oxidative stability of melt processed polyethylene composites with the two fullerenes C60 and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was studied with the aim of comparing the stabilization effect of both fullerenes on three different polyethylenes (PE). The results obtained show that, irrespective of the specific polyethylene being considered, C60 loadings as low as 1.0 wt% cause a dramatic increase in the thermo-oxidative stability of the corresponding composites (up to 64.8 °C at T2% and 113.8 °C at T5%, TX% being the temperature corresponding to a mass loss of X wt%), in agreement with previous reports. Furthermore, and more importantly, this work shows for the first time that the thermo-oxidation stability effect caused by PCBM is even higher than that of C60, the difference between both being particularly significant in the early stages of degradation, i.e. for mass losses ≤2 wt%. For example, polyethylene composites with 1.0 wt% PCBM show T2% values which are systematically higher than those of the corresponding composites with 1.0 wt% C60, the difference between the T2% values of the two composites being 38.8 °C, 67.1 °C and 26.4 °C in the three different polyethylenes considered. Therefore, when compared with C60, PCBM is particularly more effective at delaying the beginning of the thermo-oxidative degradation. According to our results, PCBM loadings as low as 1.0 wt% can increase the thermo-oxidative stability of polyethylene composites by more than 130 °C and these are, as far as we know, the highest thermo-oxidative stability results induced by nanoparticles ever reported in the literature for polyethylene.

Efficiency of curcumin, a natural antioxidant, in the processing stabilization of PE: Concentration effects

The stabilising efficiency of curcumin was studied in polyethylene during processing and under oxygen at high temperature. The effect of the natural antioxidant was investigated at concentrations of 0–1000 ppm in combination with a phosphonite secondary antioxidant (Sandostab P-EPQ) of 1000 and 2000 ppm, respectively. The polymer was homogenized with the additives then processed by six consecutive extrusions taking samples after each processing step. The samples were characterized by FT-IR spectroscopy, melt flow index, colour, and OIT measurements. Compared to the effect of pure phosphorous antioxidant, the melt stability of PE is increased already at 5 ppm curcumin content. The melt as well as the high temperature oxidative stability (OIT) of the polymer are controlled by both types of antioxidants. Curcumin hinders the oxidation of polyethylene and the formation of long chain branches during processing, which can be attributed to the fact that curcumin is not only a hydrogen donor but its unsaturated linear moiety can also scavenge alkyl and oxygen centred macroradicals. Curcumin discolours polyethylene already at small concentrations but the colour fades with increasing number of extrusions.

Chemiluminescence studies on comparison of antioxidant effectiveness on multiextruded polyethylenes

Several polyethylene resins; high density polyethylene (Ph-HDPE, Phillips metal oxide catalyst) and linear low density polyethytlenes (LLDPE, formed using Ziegler–Natta catalyst and metallocene catalyst technology, m-LLDPE) were used in order to acquire an insight in to the effect of different polymerization catalyst systems on the melt stabilization performance of single AO. Chemiluminescence (CL) and melt flow rate (MFR) were used to analyze the degradation as a function of the number of passes through a twin-screw extruder. A good correlation was obtained, and the additives resulting with the best melt flow stability in the polymer were the same as those that promote the best CL results.