Yonghong Ma

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.

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.

Isolation and Characterization of Cellulose Fibers from Rice Straw and its Application in Modified Polypropylene Composites

In this work, cellulose fibers from rice straw were isolated by a mechanical–high pressure steam technique, and were filled into polypropylene (PP) as a modifier. The structure and morphology of untreated and treated rice straw fibers were characterized by using Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and X–ray diffraction (XRD). The thermal properties, rheological behaviors and mechanical properties of the PP composites filled with untreated and treated straw fibers were investigated. The results show that the hemicelluloses and lignin can be removed from the structure of fibers by pretreatment. XRD curves reveal that this results in improving the crystallinity of the fibers. Compared with untreated rice straw fibers, PP composites filled with treated rice straw fibers exhibit higher thermal stability. The complex viscosity values of the composites decrease because of the pretreatment. Pretreatment can significantly improve tensile strength, elongation at break and impact strength of PP/rice straw fibers composites due to its enhanced interfacial adhesion between the PP matrix and rice straw fibers.

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.

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.

Combustion characteristics and thermal properties of high-density polyethylene/ethylene vinyl-acetate copolymer blends containing magnesium hydroxide

Magnesium hydroxide (MH) was added into high-density polyethylene (HDPE)/ethylene vinyl-acetate (EVA) copolymer blends with various MH contents (30–60 wt%) to improve the flame retardancy of HDPE/EVA blends. The flammability, morphology of charred residues, thermal stability, crystallization, and mechanical properties of HDPE/EVA/MH composites were investigated by UL-94 test, limiting oxygen index (LOI), cone calorimeter test (CCT), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and tensile test. The data obtained from LOI, UL-94 test, and CCT revealed that the addition of MH provided improvements in flame retardancy by increasing the LOI values, UL-94 rating, and reducing heat release, carbon monoxide and carbon dioxide emissions along with delayed ignition with increasing the content of MH. The UL-94 V-0 rating and high LOI value were achieved with the incorporation of MH at a loading level higher than 50 wt% in HDPE/EVA blends, which suggested that the formation of intact, consolidated, and thick residue structures on the surfaces of MH-filled composites prevented the underlying polymer materials from burning. DSC results showed that the crystallinity of HDPE/EVA blends increased with increasing the content of MH, resulting in the enhancement of the strength of HDPE/EVA/MH composites. The thermal stability of HDPE/EVA blends decreased due to the addition of MH.