Thermal Stability Of Polypropylene Research Articles

PP/MWCNTs composites: Effects of length of MWCNTs on isothermal crystallization behaviors, crystalline structure, and thermal stability

This study adopts the melt compounding method to prepare /mutli-walled carbon nanotubes composites. The effects of different lengths of the mutli-walled carbon nanotubes on the isothermal crystallization behaviors, crystalline structure, and thermal stability of the polypropylene/mutli-walled carbon nanotubes composites are examined. The PLM results show that the combination of mutli-walled carbon nanotubes prevents the growth of polypropylene spherulites, and thus results in a small size of spherulites. The differential scanning calorimetry results show that the short (S-) or long (L-) mutli-walled carbon nanotubes can function as the nucleating agent of polypropylene, which accelerates the crystallization rate of polypropylene. Avrami theory analyses indicate that the addition of short-mutli-walled carbon nanotubes particularly provides polypropylene/mutli-walled carbon nanotubes composites with a high crystallization rate. The X-ray diffraction results show that the combination of mutli-walled carbon nanotubes does not pertain to the crystal structure. The TGA test results show that long-mutli-walled carbon nanotubes outperform short -mutli-walled carbon nanotubes in improving the thermal stability of polypropylene, and both can significantly improve it.

Thermal Stability, Combustion Behavior, and Mechanical Property in a Flame-Retardant Polypropylene System

In order to comprehensively improve the strength, toughness, flame retardancy, smoke suppression, and thermal stability of polypropylene (PP), layered double hydroxide (LDH) Ni0.2Mg2.8Al–LDH was synthesized by a coprecipitation method coupled with the microwave-hydrothermal treatment. The X-ray diffraction (XRD), morphology, mechanical, thermal, and fire properties for PP composites containing 1 wt %–20 wt % Ni0.2Mg2.8Al–LDH were investigated. The cone calorimeter tests confirm that the peak heat release rate (pk–HRR) of PP–20%LDH was decreased to 500 kW/m2 from the 1057 kW/m2 of PP. The pk–HRR, average mass loss rate (AMLR) and effective heat of combustion (EHC) analysis indicates that the condensed phase fire retardant mechanism of Ni0.2Mg2.8Al–LDH in the composites. The production rate and mean release yield of CO for composites gradually decrease as Ni0.2Mg2.8Al–LDH increases in the PP matrix. Thermal analysis indicates that the decomposition temperature for PP–5%LDH and PP–10%LDH is 34 °C higher than that of the pure PP. The mechanical tests reveal that the tensile strength of PP–1%LDH is 7.9 MPa higher than that of the pure PP. Furthermore, the elongation at break of PP–10%LDH is 361% higher than PP. In this work, the synthetic LDH Ni0.2Mg2.8Al–LDH can be used as a flame retardant, smoke suppressant, thermal stabilizer, reinforcing, and toughening agent of PP products.

Layered double hydroxide-oxidized carbon nanotube hybrids as highly efficient flame retardant nanofillers for polypropylene.

Aqueous miscible organic layered double hydroxides (AMO-LDHs) can act as organophilic inorganic flame retardant nanofillers for unmodified non-polar polymers. In this contribution, AMO [Mg3Al(OH)8](CO3)0.5·yH2O LDH–oxidized carbon nanotube (AMO-LDH–OCNT) hybrids are shown to perform better than the equivalent pure AMO-LDH. A synergistic effect between the AMO-LDH and OCNT was observed; this endows the hybrid material with enhanced flame retardancy, thermal stability, and mechanical properties. The thermal stability of polypropylene (PP) was significantly enhanced by adding AMO-LDH–OCNT hybrids. For PP mixed with AMO-LDH–OCNT hybrids to produce a composite with 10 wt% LDH and 2 wt% OCNT, the 50% weight loss temperature was increased by 43 °C. Further, a system with 10 wt% of AMO-LDH and 1 wt% OCNT showed a peak heat release rate (PHRR) reduction of 40%, greater than the PHRR reduction with PP/20 wt% AMO-LDH (31%). The degree of dispersion (mixability) between AMO-LDH and OCNT has a significant effect on the flame retardant performance of the hybrids. In addition, the incorporation of AMO-LDH–OCNT hybrids led to better mechanical properties, such as higher tensile strength (27.5 MPa) and elongation at break (17.9%), than those composites containing only AMO-LDH (25.6 MPa and 7.5%, respectively).

Effect of modified layered double hydroxide on the flammability and mechanical properties of polypropylene

Abstract Copper-aluminum layered double hydroxides (Cu-LDHs) and nickel-aluminum layered double hydroxides (Ni-LDHs) were synthesized using co-precipitation method. LDHs were organically modified by long chain sodium stearate. Polypropylene (PP)/layered double hydroxides (LDHs) and polypropylene (PP)/organically-modified layered double hydroxides (m.Cu-LDHs or m.Ni-LDHs) were prepared through the melt bending of the PP with either nanosized LDHs or m.LDHs without any other additives. The effect of stearate on the dispersibility of LDHs was investigated by X-ray diffraction (XRD). The surface morphology of LDHs was also studied using scanning electron microscope (SEM), and the thermal stability properties of PP/LDHs composites were studied by thermogravimetric analysis (TGA). The mechanical properties of the PP/LDH composites, tensile strength, and modulus of elasticity were investigated. The flammability properties were investigated using the cone calorimeter test. The intercalation of modified LDHs was determined by XRD in the presence of stearate. Results showed that modified LDHs presented good disperasbility in the PP matrix. The thermal stability of PP has been improved by up to 6% using m.Ni-LDHS. Unmodified and modified nanosized LDHs decreased the fire growth rate of PP from 10.8 kW/m2.s to 4.1 kW/m2.s and 4.5 kW/m2.s, respectively.

Mechanical and flammability characterisations of biochar/polypropylene biocomposites

Abstract Biocomposites were manufactured with biochar and polypropylene at five loading levels (0, 15, 25, 30, and 35 wt%) by compounding and injection moulding. Biocomposites were tested by tension, bending, cone calorimeter, thermogravimetry, differential scanning calorimetry, X–ray diffraction, and infrared spectroscopy. Incorporation of increasing amount of biochar to neat polypropylene continuously improved its tensile modulus and flexural strength/modulus. The peak heat release rate and smoke production of the biocomposites were significantly reduced as a result of biochar addition. The high surface area of biochar allowed polypropylene to flow in creating a mechanical interlocking and improving the mechanical properties. The thermally stable biochar provided a compact char structure during combustion which prevented the heat and mass transfer between the polypropylene and the ambient O2. Thermal stability of polypropylene was increased as a result of biochar inclusion, as observed in thermogravimetry.

Non-isothermal degradation kinetics and morphology of PP/TiO2 nanocomposites using titanium n-butoxide precursor

This study investigates the influence of the addition of TiO2, obtained by hydrolysis–condensation reaction of titanium dioxide precursors, on the kinetics of polypropylene (PP) Non-Isothermal Degradation. The dispersion of nanoparticle and its relation to the degree of crystallinity by XRD also was investigated. The results indicated that the addition of the TiO2 increased the degree of crystallinity of PP and there was an increase of the E ad which may be associated with an increase in thermal stability. As could be seen the TEM micrographs showed nanoparticles of TiO2 with regions homogeneously distributed and some also aggregated. In degradation kinetics, the nanocomposites could demonstrate an increase in the thermal stability of PP in the initial mass loss stages, so that, the PP/TiO2b1,5 nanocomposites were the sample that showed better influence the thermal stability 100 °C in T onset . The nanoparticles by presenting a good dispersion in the PP matrix may difficult the volatile products diffusion.

Synergistic effect of Ni-based bimetallic catalyst with intumescent flame retardant on flame retardancy and thermal stability of polypropylene

Ni-based bimetallic catalysts were prepared and used as catalysts and synergistic agents to improve the flame retardancy of intumescent flame retardants (IFR) systems based on ammonium polyphosphate (APP) and pentaerythritol (PER) in polypropylene (PP). The synergistic effects of Ni-based bimetallic catalysts were evaluated by limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), fourier transform infrared (FTIR), energy dispersive spectrometer (EDS). It was found that the addition of Ni-based bimetallic catalysts could dramatically enhance LOI value and improve UL-94 rating. Among all the bimetallic catalysts, NiMg catalyst exhibited the best synergistic effect. Only 2 wt% of NiMg catalyst could promote the LOI value of PP/IFR composite from 29.0% to 38.1%. What's more, the introduction of Ni-based catalysts led to great reduction in heat release rate (HRR), total heat release (THR), rate of smoke release (RSR), total smoke release (TSR), with a simultaneous increase in residual char. The TGA curves showed that the presence of Ni-based catalysts could also improve the stability of the char in high temperature. The FTIR curves and EDS analysis indicated that Ni-based bimetallic catalysts could promote the formation of POP and POC, leaving more P, N and O in the condensed phase, and thus giving rise to more crosslinks of the char. SEM observations further confirmed Ni-based bimetallic catalyst could help to form a more compact and homogeneous char layer and effectively reduce the heat and oxygen transfer, resulting in better flame retardancy of PP/IFR composites.

Synergistic effect of expandable graphite and intumescent flame retardants on the flame retardancy and thermal stability of polypropylene

In this article, the investigation mainly focuses on the synergistic effect of expandable graphite (EG) and intumescent flame retardants in improving the flame retardancy of polypropylene (PP). The ratio of melamine polyphosphate (MPP) and dipentaerythritol (DPER) has been studied by limiting oxygen index (LOI) and vertical burning test (UL-94) tests. The results demonstrate that the optimal ratio of MPP and DPER in flame-retarding PP was 3/1. Except that, the incorporation of EG into the PP/MPP/DPER system can greatly improve the flame-retardant properties of PP materials. When the content of EG is 10 wt%, LOI value of PP composites reaches 33.2 % and obtains V-0 rating in UL-94 tests. Furthermore, Fourier transform infrared spectra (FTIR) indicate that the main char-formation process of this system occurs at 350–400 °C. And char residue for PP composites after combustion was systematically analyzed by FTIR and X-ray photoelectron spectroscopy spectra. Based on these facts, a potential condensed flame-retardant mechanism was primarily proposed.

Thermal properties and thermal stability of PP/MWCNT composites

The effects of the filler size and content on thermal properties and thermal stability of polypropylene (PP) composites filled with four different sizes of multi-walled carbon nanotubes (MWCNTs) were investigated through thermogravimetric analysis. The results showed that the values of the decomposition temperature increased with increasing weight fraction and length–diameter ratio of the filler, while increased with decreasing filler diameter. The values of the residues increased approximately linearly with increasing filler weight fraction. The values of maximum mass loss rate decreased roughly with increasing filler weight fraction, while the influence of the filler diameter and length–diameter ratio on the maximum mass loss rate was insignificant. The thermal stability improvement might be attributed to the barrier function of the MWCNTs. This study provides a basis for further development of MWCNTs reinforced polymer composites with desirable thermal properties for potential application as energy materials.

Preparation and characterization of candelilla fiber (Euphorbia antisyphilitica) and its reinforcing effect in polypropylene composites

Candelilla bagasse fiber (CBF) was prepared by a mesh sieve and ball-milling process and its reinforcing effect in a polymer matrix analyzed. Composites of polypropylene (PP) and CBF were prepared by melt blending with varying amounts (20, 25, and 30 wt%) of fiber using maleic anhydride PP as coupling agent. The chemical composition of CBF was analyzed according to Technological Association of the Pulp and Paper Industry (TAPPI) methods, and the morphology and thermal and chemical properties of CBF and its composites were analyzed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and tensile testing. In general, fibers extracted from candelilla by a reduction process are comparable in terms of micro- and nanostructure to other lignocellulosic fibers. Dynamic light scattering (DLS) results reveal that sieve-milling reduces the fiber size. The results also show that the thermal stability of PP was enhanced when using CBF, but the crystallinity index of the PP composites decreased slightly according to DSC and XRD results. Furthermore, the Young’s modulus was increased in PP/CBF samples with and without MAPP to obtain improved wettability and fiber–polymer adhesion. We found that CBF is an excellent alternative to replace conventional materials or synthetic fibers, as well as for reinforcement in polymer composites.

Thermal Behavior of Polypropylene-g-glycidyl Methacrylate Prepared by Melt Grafting

The thermal behaviors of glycidyl methacrylate (GMA)-grafted polypropylene (PP) (PP-g-GMA) with two different grafting degrees, namely, GPP1 and GPP2, were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), wide-angle X-ray diffraction (WAXD), dynamic mechanical analysis (DMA), and thermogravimetrical analysis (TGA). DSC results suggested that the GMA grafted PP exhibited higher crystallization temperature Tc, higher melting temperature Tm, and higher crystallinity compared with the neat PP. The isothermal crystallization kinetics was analyzed with the Avrami equation and the total crystallization activation energy was calculated. It was concluded that the crystallization processes of PP and the grafted PP were controlled by nucleation and the values of the crystallization activation energy of PP and the grafted PP were almost identical. POM results suggested that the GMA grafted PP exhibited smaller spherulites size compared with the neat PP. WAXD patterns indicated that the neat PP encouraged the formation of γ phase, compared with the grafted PP, during the crystallization process. DMA results showed that melt grafting did not induce a clear effect on the γ-transition and β-transition of the amorphous phase but resulted in a decrease in mobility of the PP chains in the crystals. TGA curves suggested that the melt grafting slightly improved the thermal stability of PP.

Resistance to Thermal Degradation of Polypropylene in Presence of Nano Zinc Oxide

Polypropylene/zinc oxide composites were prepared using melt mixing method and made into sheets using compression moulding. 0–5 wt% of zinc oxide (ZnO) with different crystallite sizes were incorporated into the polypropylene (PP). Mechanical properties of the PP were increased by the addition of ZnO. Morphology of the composites showed good dispersion of ZnO in the composites. Thermal ageing was carried out on neat PP and composites for 24 hrs. Mechanical properties of the PP and composites were decreased after thermal ageing. However composites showed increased properties compared to neat PP even after thermal ageing. IR studies indicated better thermal stability of PP in presence of ZnO. PP filled with less crystallite size ZnO showed better properties compared to PP filled with high crystallite size ZnO and neat PP.

Direct growth of layered double hydroxides in an aqueous suspension of carbon nanotubes and their application as fillers in polypropylene

Abstract Interesting composites with three-dimensional (3D) structure that combine one-dimensional (1D) carbon nanotubes (CNTs) with two-dimensional (2D) lamellar flakes show excellent potential properties for application in polymer matrices. Herein, we describe the construction of a composite of CNTs and 2D flakes by in situ growth of layered double hydroxides (LDH) in CNTs aqueous suspensions. It has been found that the morphology of the LDH/CNTs composites can be easily tuned by changing the CNTs concentration ( C CNTs ) and the LDH growth time. The introduction of CNTs did not severely perturb the main crystalline structure of LDH. A plausible model for the in situ growth mechanism is proposed to describe the temporal evolution of the LDH morphology as well as the influence of C CNTs on the morphology of the LDH/CNTs composites. The as-obtained LDH/CNTs 3D composites with interlayer dodecyl-benzenesulfonate anions have proved to be efficient fillers, significantly improving the mechanical properties and thermal stability of polypropylene (PP).

Synergistic effect between a novel triazine charring agent and ammonium polyphosphate on flame retardancy and thermal behavior of polypropylene

Abstract A novel oligomeric charring agent (PTCA) containing triazine and diphenyl group was synthesized by cyanuric trichloride, diphenylamine and ethylenediamine through nucleophilic reaction. The structure and thermal stability of PTCA were characterized by Fourier transform infrared spectrometry (FT-IR), element analysis testing and thermogravimetric analysis (TGA). The effectiveness of the novel intumescent flame retardant system (ammonium polyphosphate and PTCA, abbrev. IFRs) on fire retardancy and thermal stability of polypropylene (PP) was investigated through UL-94, limiting oxygen index (LOI) tests, cone calorimeter tests and thermogravimetric analysis (TGA). UL-94 vertical burning test revealed that the addition of 20 wt% IFRs into neat PP was enough to reach V-0 rating. LOI value of PP by addition of 20 wt% IFRs rose from 17.5 to 31 vol%. Moreover, a remarkable decrease in peak heat release rate (PHRR: −90%), total heat release (THR: −54%) and total smoke release (TSR: −51%) was revealed when the loading of IFRs was 20 wt%. TGA results showed that PTCA presented good char formation ability, and it would greatly increase the thermal stability of PP when combined with APP. The Fourier transformed infrared spectra (FTIR) revealed that the flame retardant mechanism might be ascribed to aromatic and phosphoric char formed during combustion. Additionally, the structure and morphology of char residues were further studied by SEM and Raman spectra.

Multi-Component Composites Based on Polypropylene, Ethylene-Octene Copolymer and Zinc Oxide

Multi-component blends of polypropylene (PP), ethylene-1-octene copolymer (EOC) and zinc oxide (ZnO) are prepared by melt mixing using two-roll mill. Samples prepared by compression moulding have been investigated by using differential scanning calorimeter (DSC). It is found that addition of ZnO particles decreases PP melting point and increases crystallinity degree of PP. ZnO works as nucleation agent for PP by increasing quantity of crystallization centers, but at the same time decreasing structure quality. Because of the structure change mechanical properties are affected. At lower nanoparticle concentration some reinforcement effect I observed, while at higher particles concentration brittlening occurs. Crystalline structure and particles nature increases thermal stability of PP and PP/EOC blends.

Thermal decomposition kinetics of multiwalled carbon nanotube/polypropylene nanocomposites

The multiwalled carbon nanotube (MWCNT)/polypropylene (PP) nanocomposites with different MWCNT contents were prepared by a melt-mixing method, and their thermal decomposition kinetics has been studied. As the properties of MWCNT/PP nanocomposites fundamentally depend on the dispersion state of MWCNTs in the PP matrix, rheological measurement and field emission electron microscopy were used to examine the dispersion state of MWCNTs in the PP matrix. The effect of MWCNTs on the thermal stability of PP in MWCNT/PP nanocomposites was studied at different heating rates by means of thermogravimetric (TG) analysis. Based on the TG results, the Ozawa’s method was used for the determination of the activation energies required in the thermal decomposition of MWCNT/PP nanocomposites. The Kissinger’s method was also applied to verify the results. Both methods proved that the thermal stability of PP could be significantly improved in the presence of MWCNTs.

Synthesis of a Novel Triazine-Based Hyperbranched Char Foaming Agent and the Study of Its Enhancement on Flame Retardancy and Thermal Stability of Polypropylene

A novel hyperbranched char foaming agent (HCFA), successfully synthesized via the polycondensation of 2-chloro-4,6-di-(2-hydroxyethylamino)-s-triazine (CHT), was combined with ammonium polyphosphate (APP) to endow polypropylene (PP) with flame retardance. The study of thermal stability of various PP composites showed that HCFA/APP system could effectively improve the thermal degradation and thermal-oxidative stability of the char residues, and PP3 containing 30 wt % APP/HCFA with a 3/1 weight ratio left the highest amount of char residue at 700 °C. The results of flammability revealed that PP3 had the most effective flame retardancy and lowest fire hazards. The investigation of structure and morphology of char residues indicated that the compact and foaming char layer, as a good barrier against the transmission of heat and volatiles, was formed for PP3 during combustion.

Thermal degradation behavior of polypropylene base wood plastic composites hybridized with metal (aluminum, magnesium) hydroxides

ABSTRACTThe effect of hybridization of wood fibers and metal hydroxides on the thermal stability of polypropylene (PP) based plastic composites is studied through thermo gravimetric analysis (TGA). The wood fiber increases thermal stability of the metal hydroxide hybridized WPC including aluminum hydroxide (AH) and magnesium hydroxide (MH). Hybridization with the AH increases decomposition temperature of the maximum loss rate (Tmax) of the PP due to reinforcement of residue, but the onset‐temperature of the PP decomposition is nearly shifted. However, hybridization with the MH increases both the onset‐temperature and theTmaxof the PP thermal degradation. Both AH and MH fillers increase theTmaxof the PP matrix decomposition with increment of their contents. Besides, the MH case shows higher thermal stability of the PP resin in WPC decomposition than the AH case at the same loading level. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2014,131, 40120.

Thermally More Durable Electromechanical Films by POSS Nanomodification

The thermal stability of polypropylene (PP) based cellular electromechanical films was improved by compounding PP with thermally more durable cyclo olefin copolymer (COC) and polyhedral oligomeric silsesquioxane (POSS) nanochemical. The cast films were biaxially oriented in laboratory scale and then expanded by a gas diffusion expansion method, which increased the pore size inside the cellular film structure and the thickness of the film. The cellular films were then electrostatically charged by a contact charging method and metallized by gold sputtering. The samples were aged at 85°C showing that the d33 signal decreased from the original value, but remained at high level; more than 120 pC/N even after two weeks of ageing.

Novel polypropylene biocomposites reinforced with carbon nanotubes and hydroxyapatite nanorods for bone replacements

Multi-walled carbon nanotubes (MWNTs) of 0.1 and 0.3wt.% and hydoxyapatite nanorods (nHAs) of 8–20wt.% were incorporated into polypropylene (PP) to form biocomposites using melt-compounding and injection molding techniques. The structural, mechanical, thermal and in vitro cell responses of the PP/MWNT–nHA hybrids were investigated. Tensile and impact tests demonstrated that the MWNT additions are beneficial in enhancing the stiffness, tensile strength and impact toughness of the PP/nHA nanocomposites. According to thermal analysis, the nHA and MWNT fillers were found to be very effective to improve dimensional and thermal stability of PP. The results of osteoblast cell cultivation and dimethyl thiazolyl diphenyl tetrazolium (MTT) tests showed that the PP/MWNT–nHA nanocomposites are biocompatible. Such novel PP/MWNT–nHA hybrids are considered to be potential biomaterials for making orthopedic bone implants.