Polypropylene (PP) is incorporated with four different grades (H100, M25, M5, and C300) of graphene nanoplatelets (GnPs) via twin screw extrusion followed by injection moulding. The composites’ thermal stability, crystallization behaviour, tensile strength, and electrical property are carefully examined. The thermal stability is significantly enhanced with the incorporation of small-sized GnPs as shown by the 11.2% improvement in T5% (the temperature at which 5 wt% of the mass loss occurs) and 5.1% improvement in Tmax (the temperature at which the maximum loss rate occurs). The thermal stabilizing effect of fillers can be significantly enhanced when they are well distributed with less aggregation as is the case for small-sized GnPs. The GnPs show a considerable nucleating effect on PP by increasing the crystallization temperature (Tc). The greatest improvement in tensile property is achieved with the use of small-sized GnPs. A 33.0% enhancement in tensile strength and 59.1% improvement of tensile modulus are obtained with the use of C300 and M5, respectively. The significantly increased thermal stability and mechanical property with small-sized GnPs are due to the fact that these small-sized fillers achieve a high degree of dispersion with less agglomeration as shown in the scanning electron microscope (SEM) images. However, the fillers with a large sheet size are still beneficial for purposes concerning electrical conductivity since the lowest percolation is obtained with H100. The greater the size of the GnPs, the smaller the percolation threshold of composites is exhibited.
This study investigated the effects of ammonium polyphosphate (APP) content on the mechanical, thermal and flammability properties of kenaf/polypropylene (KF/PP) and rice husk/polypropylene (RH/PP) composites prepared by melt mixing technique. Polyethyleneoctene grafted maleic anhydride (POE-g-MAH) has been used as compatibilizer. The PP/KF/APP and PP/RH/APP composites were investigated using flexural and impact tests, scanning electron microscope, thermogravimetric analysis (TGA), differential scanning calorimeter and limiting oxygen index (LOI) test. Flexural modulus of PP/KF/APP and PP/RH/APP composites significantly improved from approximately 1.1–2.5 and 0.9–2.1 GPa, respectively, by the addition of 10 phr APP. The flexural strength of the composites also increased by the incorporation of 10 phr APP. In addition, the impact strength of the PP/RH/APP composites increased above 10 phr APP content. From the TGA results, incorporation of APP into PP/RH and PP/KF composites increased the char residue and thermal stability of the composites. Furthermore, the addition of APP increased the flame retardancy of the PP/KF/APP and PP/RH/APP composites with a significant increase of LOI at 10 phr.
Polypropylene (PP) is one of the most widely used commodity polymer. However, it has a low upper service temperature. Addressing this challenge, we introduced reactive blending of PP, maleic anhydride-grafted PP (PP-g-MA) and (3-aminopropyl)triethoxysilane (3APTES) in the presence of nanoclay, which results in a highly nucleated PP composite with improved dimensional stability. At the processing temperature, the reaction between maleic anhydride, which is already grafted on the PP chain, and 3APTES forms N-substituted maleimide-grafted PP. The results indicated that the introduction of branched structures on PP chains increased the chain bulkiness and led to the formation of stable nuclei that initiate crystallization at high temperatures. By offering nucleating sites, the dispersed nanoclay particles facilitated the nucleation process to a greater extent. Compared with the neat polymer matrix, the crystallization temperature of the composite was 15.5 °C higher with moderate improvements in the heat distortion and Vicat softening temperatures. This is most likely the first report where such an improvement in crystallization temperature has been achieved for isotactic PP homopolymers. In summary, reactive processing of the PP/nanoclay composite in the presence of PP-g-MA and 3APTES has potential for the development of high-performance PP-based advanced materials.
This study experimentally investigated that the inerting effect of Ammonium Polyphosphate (APP) on characteristics of Polypropylene (PP) dust explosion. The results indicated that the maximum explosion pressure (Pmax), the explosion index (Kst) and the minimum explosion concentration (MEC) of PP powders were 8 bar, 257 bar ms and 25 gm(3), respectively. Moreover, the minimum ignition energy (MIE) and the minimum ignition temperature (MIT) were 10 mJ and 335 degrees C, correspondingly for PP dust cloud. The explosion of PP powders could be inerted completely by 80 wt% APP. In addition, the MIE of PP powders increased when the mass fraction of APP increased. Furthermore, APP had a significant inerting effect on the MIT of PP dust cloud. The MIT of PP powders increased by 80 degrees C when the mass fraction of APP increased to 80 wt %.Thermal analysis results showed that the introduction of APP could improve the thermal stability of PP. Furthermore, thermogravimetric analysisinfrared (TGIR) spectroscopy was employed to gain insights into the pyrolysis mechanism of the PPAPP mixtures. The TGIR results showed that the volatilized products formed in the pyrolysis were H2O and NH3 which could dilute and consume oxygen in gas phase. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
In this study, an efficient novel allylamine polyphosphate (AAPP) as a flame retardant (FR) crosslinker is used to improve the thermal stability of flame retarded polypropylene (PP) composites under electron beam treatment. First, a multifunctional AAPP has been designed and synthesized via a simple ion exchange reaction of the common ammonium polyphosphate (APP). AAPP was mixed with PP via a twin-screw extruder to prepare a series of flame retarded PP composites. Afterwards these composites were irradiated with high energy electrons in order to increase their thermal stability. The results showed an increased LOI value of PP/AAPP composites and effective melt dripping resistance in the UL-94 test in comparison with traditional PP/ammonium polyphosphate (APP) composites. Moreover, CC data like the heat release rate (HRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) showed that AAPP had a much better contribution to the flame retardation of PP than APP. Besides, AAPP provided an excellent quality of char residue in the combustion stage due to its P-N-C and P-O-C structures. Moreover, the environment-friendly electron beam technology was an efficient approach to improve the thermal stability of these multifunctional flame retarded PP composites without the use of additional stabilizers. This innovative idea may be expanded to other polymer systems to develop high performance polymer composites by environment-friendly electron beam technology.
In this work a novel functional modifier for clay with increased thermal stability and synergistic effect on the flame retardancy of intumescent flame retardant polypropylene (IFR PP) composites was developed. First, triphenyl(undec-10-enyl)phosphonium bromide (TPB) was synthesized and characterized by FT-IR and 1H NMR spectroscopy. TPB has a high thermal stability with an initial decomposition temperature of about 270°C. Subsequently, TPB was used to prepare functional organoclay (OC) by cation exchange reaction. OC was characterized by thermogravimetric analysis (TGA) and wide-angle X-ray scattering (WAXS). The interlayer distance of novel OC increased to 1.85nm. OC was used in IFR PP nanocomposites prepared by melt mixing. The morphology, thermal stability and fire behavior of these IFR PP nanocomposites were investigated by SEM, TEM, TGA, limiting oxygen index (LOI), vertical burning test (UL94), and cone calorimeter (CC) test. In comparison to IFR (18wt%) PP composites, IFR (16wt%)+OC (2wt%) PP nanocomposites passed the UL94 V-0 rating and showed no dripping. The LOI value decreased from 30.5 to 28.8 due to the use of low molar mass TBP. It was shown by cone calorimeter tests that the additional used of 1 or 2wt% OC leads to a reduced heat release rate, smoke production rate and total smoke production. All these experimental results showed that this novel OC provided an excellent synergistic effect on the flame retardancy of IFR PP composites. Finally, electron beam treatment was used to enhance the thermal stability of flame retardant nanocomposites.
In order to investigate whether the particle sizes of inorganic additives in polymer have an influence on the flame-retardant and other properties of the polymer, five types of Mg3Al–CO3 layered double hydroxide (LDHs) with particle diameters of 80–100, 200–350, 500–550, 550–600, and 700–900 nm were synthesized using a hydrothermal method. The obtained Mg3Al–CO3 LDHs were treated using the aqueous miscible organic solvent treatment method to give highly dispersed platelets in Polypropylene (PP). The thermal stability, flame retardancy, and mechanical properties of the PP/AMO–LDH nanocomposites were investigated systematically. The results showed that the thermal stability and flame retardancy of PP could be improved after incorporating AMO–LDHs. The temperature at 50% weight loss (T0.5) of PP/LDH (700–900 nm) nanocomposites with a LDH loading of 15 wt % was increased by 57 °C. When the LDHs loading was 40 wt %, the peak heat release rate (PHRR) of the PP/LDH nanocomposites with small LDHs particle sizes (<350 nm) was decreased by ca. 58%. The limiting oxygen index was increased by 5% for PP/LDH (80–100 nm) nanocomposites. The response surface regression results also indicated that both LDH particle size and loading have influence on PHRR, heat release capacity, tensile strength, and elongation at break.
The thermal stability and migration resistance of light stabilizers are vital for their applications in plastics. Herein, a novel nano organicinorganic hybrid light stabilizer with high thermal stability and low solubility was prepared by intercalating a synthesized hindered amine light stabilizer (HALS) with UV absorption capability into the interlayer galleries of MgAl layered double hydroxides (LDH) through coprecipitation method. The prepared HALSLDH was characterized by XRD, FTIR, SEM, TGDTA and UVvis, and was incorporated into the matrix of polypropylene (PP) via solvent casting method to prepare LDHPP composite for light stability test. It was found that the synthesized HALS was successfully intercalated into the interlayer galleries of MgAlLDH, forming an organicinorganic hybrid material HALSLDH with a mean size of 63 nm. HALSLDH nanosheets were evenly dispersed in the matrix of PP, and the addition of HALSLDH can retard the thermal decomposition of PP. Moreover, the incorporation of HALSLDH significantly improved the light stability of PP and reduced the photo degradation of PP by about 83.2%. Therefore, the prepared novel HALSLDH has potential application in the field of PP as an efficient and promising light stabilizer.