Xiaolang Chen

Influences of coupling agent on thermal properties, flammability and mechanical properties of polypropylene/thermoplastic polyurethanes composites filled with expanded graphite

In this study, polypropylene (PP)/thermoplastic polyurethanes (TPU) filled with inorganic intumescent flame retardant expanded graphite (EG) was prepared by melt blending in a twin-screw extruder. The thermal stability, fire retardancy, mechanical properties, and fracture morphology of PP/TPU composites with treated and untreated EG were investigated by thermogravimetric analysis, cone calorimeter, and scanning electron microscope. The results showed that both untreated and treated EG can greatly enhance the thermal stability and fire resistance of polymer matrix materials. Compared with untreated EG, treated EG can further improve the flame retardancy of the composites. For example, treated EG can further reduce the heat release rate, total heat release, and CO emissions of the composites in the combustion. Surface treatment of EG could significantly improve elongation at break and impact strength of PP/TPU/EG composites due to its enhanced interfacial adhesion and the good dispersion of EG particles in the polymer matrix.

Combustion Behaviour and Synergistic Effect of Zinc Borate and Microencapsulated Red Phosphorus with Magnesium Hydroxide in Flame-Retarded Polypropylene Composites

In this paper, the limiting oxygen index (LOI), Underwriters’ Laboratories-94 (UL-94) test, cone calorimeter test (CCT), and thermogravimetric analysis (TGA) were used to study the flame-retardant properties of polypropylene (PP) composites and the synergistic flame-retardant effects of zinc borate (ZB) and/or microencapsulated red phosphorus (MRP) with modified magnesium hydroxide (MH) on PP. The experimental results showed that the addition of ZB and MRP had a great effect on the flammability of the PP composites. The data obtained from the CCT indicated that the heat release rate (HRR), the effective heat of combustion (EHC), and the mass loss of the flame-retarded PP composites decreased markedly with increasing addition of ZB and/or MRP. The data obtained from the TGA curves indicated that the thermal stabilities of PP/MH/ZB and PP/MH/ZB/MRP composites were better than those of PP/MH composites.

Thermal stability and combustion behavior of flame-retardant polypropylene with thermoplastic polyurethane-microencapsulated ammonium polyphosphate

In this article, thermoplastic polyurethane-microencapsulated ammonium polyphosphate (MTAPP) is prepared and well characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis (TGA). MTAPP and APP are added onto polypropylene (PP) as a novel intumescent flame-retardant system to improve the flame retardancy of PP. The flammability, thermal stability, and mechanical properties of the flame-retardant PP composites are investigated by limiting oxygen index (LOI), UL-94 vertical burning test, cone calorimeter test (CCT), TGA, and mechanical properties tests. The results show that MTAPP exhibits better flame retardancy and thermal stability than that of the APP in the flame-retardant PP composites. The LOI value of the PP/MTAPP composite at the same loading level is higher than that of PP/APP composite. The dripping of MTAPP system disappears compared with APP system from UL-94 test. The results of the CCT also indicate that MTAPP is an effective flame retardant in PP. The improvement may be attributed to the better charring capacity of MTAPP from TGA. Additionally, the mechanical properties of MTAPP are better than those of APP in PP.

Influences of organic montmorillonite on the combustion behaviors and thermal stability of polyamide 6/polystyrene blends

The nanocomposites of polyamide 6/polystyrene (PA6/PS) with different contents of organic montmorillonite (OMMT) have been obtained by melt blending. The combustion behaviors, morphology of char residues, and thermal stability of nanocomposites have been characterized by cone calorimeter tests (CCT), electron probe microanalysis, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The CCT results indicated that the OMMT was an efficient flame retardant (FR) in the FR-PA6/PS blends. The heat release rates, the total heat release, and carbon monoxide and carbon dioxide production of the FR nanocomposites decreased in comparison with PA6/PS blends. The SEM photographs showed that the “spongy” structure on the surface of char residues increased. In addition, the thickness and strength of char residues enhanced with the increase of OMMT content. The tight multilayer carbon silicate layer structure was formed which was conducive to FR. The TGA data indicated that OMMT greatly enhanced the thermal stability, and char residues of PA6/PS/OMMT nanocomposites gradually increased with increasing the OMMT content.

Effect of Red Phosphorus Masterbatch on Flame Retardancy and Thermal Stability of Polypropylene/Thermoplastic Polyurethane Blends

In this work, red phosphorus masterbatch (RPM) was filled into polypropylene/thermoplastic polyurethanes (PP/TPU) blends as a halogen-free flame retardant. The flammability behaviour, thermal stability and mechanical properties were investigated by limit oxygen index (LOI), UL-94 vertical burning, cone calorimeter tests (CCT), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results showed that the addition of RPM improved the flame retardant performance of PP/TPU blends. The LOI values of the composites with RPM were higher than that of the PP/TPU blends, and the UL-94 V-2 rating was achieved for PP/TPU/RPM composites. The CCT results further indicated that the heat release rates (HRR), total heat release (THR), and the CO2 production rate (CO2P) decreased in comparison with the PP/TPU blends. TGA data indicated that RPM greatly enhanced the thermal stability and char residues of PP/TPU blends. The addition of RPM deteriorated the tensile strength of the PP/TPU/RPM composites. However, the impact strength of the composites was improved.

Mechanical Properties and Crystallization Behavior of Polycarbonate/Polypropylene Blends

The mechanical properties, morphology, and crystallization behavior of polycarbonate (PC)/polypropylene (PP) blends, with and without compatibilizer, were studied by tensile and impact tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The tensile and impact strengths of PC/PP blends decreased with increasing the PP content due to poor compatibility between the two phases. But the addition of compatibilizer improved the mechanical properties of the PC/PP blends, and the maximum value of the mechanical properties, such as tensile and impact strengths of PC/PP (80/20 wt%) blends, were obtained when the compatibilizer was used at the amount of 4 phr. The SEM indicated that the compatibility and interfacial adhesion between PC and PP phases were enhanced. DSC results that showed the crystallization and melting peak temperatures of PP increased with the increase of the PP content, which indicated that the amorphous PC affected the crystallization behavior. However, both the PC and compatibilizer had little effect on the crystallinity of PP in PC/PP blends based on both the DSC and XRD patterns.

Efficient organic–inorganic intumescent interfacial flame retardants to prepare flame retarded polypropylene with excellent performance

In this article, an efficient and simple approach for the preparation of organic–inorganic intumescent interfacial flame retardants, aiming at enhancing the flame-retardant efficiency and interfacial adhesion between matrix and flame retardants was presented. The expandable graphite (EG) was functionalized by using a grafting process containing phosphorous, resulting in the formation of organic–inorganic intumescent flame retardants. Based on the successful grafting reaction, a series of flame-retardant polypropylene (PP) composites with different content of modified EG (MEG) were prepared and evaluated. With the incorporation of 30 wt% of MEG into PP, the satisfactory UL-94 flame retardant grade (V-0) and limiting oxygen index (LOI) as high as 25.3% were obtained. The residues of the PP/MEG composites were significantly increased with PP/EG and PP/EG/DOPO composites. Moreover, the residual char of PP/MEG composites is more compact and integrated. In addition, the formation of organic side chains on the MEG surface by the grafting reaction also contributed to an improvement in the interfacial compatibility, leading to an enhancement in mechanical properties of the composites compared with the PP composites filled with EG. The interfacial grafting flame retardants provided a novel way to prepare organic–inorganic intumescent flame retardants and the as-prepared flame retardants exhibited excellent flame retardant efficiency.

The Structure and Nonisothermal Crystallization Kinetics of HDPE Nanocomposites Filled with Mg2Al–LDH

High-density polyethylene (HDPE)/Mg2Al–layered double hydroxide (Mg2Al–LDH) nanocomposites with an ethylene-acrylic acid random copolymer (EAA)/Mg2Al–LDH master batch were prepared by melt-mixing. The structure of the nanocomposites was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results demonstrate the formation of the nanocomposites with exfoliated/intercalated layered double hydroxides well distributed in the HDPE matrix. The nonisothermal crystallization behaviour of master batch-based HDPE nanocomposites was studied by using differential scanning calorimetry (DSC). The crystallization behaviour of HDPE/Mg2Al–LDH nanocomposites was well defined by the Avrami analysis and Jeziorny method, as well as the combined Avrami and Ozawa analysis (MOs model). The results reveal that a very small amount of Mg2Al–LDH (1%) accelerates the crystallization process in comparison with the neat HDPE, and the high crystallization rate is attributed to the nucleating effect of the exfoliated nanoparticles. Overall, the exfoliated Mg2Al–LDH particles act as the nucleating agent, and therefore distinctly change the type of nucleation, growth and geometry of HDPE crystals.

The Thermal Stability and Flammability of Expandable Graphite-Filled Polypropylene/Thermoplastic Polyurethane Blends

Polypropylene/thermoplastic polyurethane (PP/TPU) blends filled with two different particle sizes (45 and 150 μm) of expandable graphite (EG) were prepared by melt blending. Thermogravimetric analysis (TGA) was carried out to explain the effect of EG on the thermal stability of PP/TPU blends. In addition, the fire behavior of PP/TPU and PP/TPU/EG was investigated by a cone calorimeter. The char morphology and carbonation of the above systems were also characterized. The experimental results indicated that intumescent EG significantly enhanced the thermal stability and fire resistance of these blends. With the smaller particle size of EG, the thermal stability and flame retardancy were improved. The results from TGA and cone calorimeter demonstrated that the addition of EG could retard the degradation of the polymer materials above the temperature of 500°C by promoting the formation of a compact char layer. This char layer prevented further degradation of the polymer matrix and protected it effectively from heat penetrating inside, resulting in lower weight loss rate and better flame-retarded performances.

Thermal Degradation and Flammability Behaviour of Hdpe/Eva/Eg Composites

In this work, high density polyethylene (HDPE), ethylene-vinyl acetate (EVA) copolymer and expandable graphite (EG) flame retardant composites were prepared by using a twin screw extruder technique. The thermal stability and flame retardant properties of the composites were investigated by the thermogravimetric analysis (TGA) and cone calorimeter, respectively. The char morphology after combustion was also further characterized. The experimental results indicated that intumescent EG greatly enhanced the thermal stability and fire resistance of polymer matrix materials. The presence of EG improved the degradation temperature of HDPE/EVA blend and increased its char residue at high temperature. The results from cone calorimeter demonstrated that the addition of EG led to the decrease of the heat release rate (HRR), total heat release (THR) and smoke production rate (SPR) of materials and could retard the emission of the toxic and flammability gases by promoting the formation of a compact char layer. This char layer will prevent the polymer matrix further degradation and protect it effectively from heat penetrating inside, resulting in lower weight loss rate and better flame retarded property.