Mengqi Tang

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.

Microencapsulated ammonium polyphosphate and its application in the flame retardant polypropylene composites

In this article, a novel intumescent alumina–silica hydrogel double shell microencapsulated ammonium polyphosphate flame retardant is prepared and filled into polypropylene as a flame retardant. The structure and properties of alumina–silica hydrogel double shell microencapsulated ammonium polyphosphate are characterized by Fourier transform infrared, scanning electron microscopy, and thermogravimetric analysis. The results show that the Al and Si groups are attached to the surface of ammonium polyphosphate. The flame retardancy, morphology of char layers, thermal properties, and mechanical properties of the polypropylene/alumina–silica hydrogel double shell microencapsulated ammonium polyphosphate composites are evaluated by limiting oxygen index, UL-94 test, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, and mechanical properties test. The results show that alumina–silica hydrogel double shell microencapsulated ammonium polyphosphate can improve the thermal stability and charred residues at high temperature. In addition, the combination of alumina–silica hydrogel double shell microencapsulated ammonium polyphosphate and polyamide 6 shows more compact, firm, and continuous charred layers, resulting in better flame retardant performances. The limiting oxygen index value for polypropylene/alumina–silica hydrogel double shell microencapsulated ammonium polyphosphate/polyamide 6 composites can reach 25.6 and obtain a UL-94 V-0 rating. Also, polypropylene/alumina–silica hydrogel double shell microencapsulated ammonium polyphosphate/polyamide 6 composites present better mechanical properties than polypropylene/ammonium polyphosphate/polyamide 6 composites at the same content of flame retardant and polyamide 6.

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.

Morphology and Thermal Property of Poly(L-Lactide)/Layered Double Hydroxides Nanocomposites via Melt Intercalation

In this work, sodium dodecyl sulfate (SDS) was used to obtain organically-modified layered double hydroxide (OMgAl-LDH) by anion-exchange reaction. The PLLA/LDH nanocomposites were prepared via direct melt intercalation. The results from both XRD patterns and FTIR spectra showed that SDS entered into the layers of LDH successfully and the layer space was increased from 0.756 to 1.64 nm. For the PLLA/LDH nanocomposites, the increase of the layer space was verified by the good dispersion of LDH in the PLLA matrix from the SEM images. The rheological analysis showed that the typical Newtonian behaviour shifted to shear-thinning behaviour with the addition of LDH. In addition, DSC data illustrated that the glass transition temperature of the PLLA/LDH nanocomposites decreased and the crystallinity of PLLA increased due to the addition of LDH, which indicates that LDH acts as a heterogeneous nucleating agent and induces the crystallization of PLLA. The modified LDH provided a better nucleating effect than the unmodified LDH. TGA results showed that OMgAl-LDH in the PLLA matrix caused earlier initial decomposition, suggesting that the presence of LDH decreased the thermal stability of the PLLA matrix.