In this article, we report the combined effects of poly(ethylene glycol) (PEG) and/or graphene oxides (GOs) on the crystallization behavior of poly(L-lactide) (PLLA) under different crystallization conditions, such as nonisothermal crystallization, isothermal crystallization, and annealing-induced cold crystallization. Differential scanning calorimetry (DSC), wide-angle X-ray diffraction, and polarized optical microscopy were used to study the crystallization kinetics and crystallinity to illustrate the effects of PEG and/ or GOs on the crystallization behavior of PLLA. The results show that PEG functioned as a plasticizer and improved the chain mobility of /PLLA during crystallization and the GOs acted as efficient nucleation agents and accelerated the crystallization rate. Finally, both PEG and GOs improved the crystallization ability of PLLA. Importantly, the simultaneous addition of PEG and GOs led to a synergistic effect on the crystallization behavior of PLLA under all conditions.

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.

In this work, the long glass fibre-reinforced poly(butylene terephthalate) (PBT) composites filled with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were prepared by melt blending, and the influence of thermo-oxidative ageing on the static and dynamic mechanical properties, thermal behaviours and morphology of composites with different ageing time at 120 °C were investigated and analysed. The results showed that the mechanical properties decreased in the primary stage of ageing, while embrittlement occurs in the later period, and the crystallinity of PBT decreases first, and then recovers to some extent. The scanning electron microscopy (SEM) photos of the samples indicated that the obvious crack appeared on the sample surface and a deeper, broader crack occurred with a longer ageing time. The results of energy dispersive X-ray analysis (EDAX) proved the DOPO filler diffused to the sample surface by measuring the content of phosphorus. Thermal gravimetric analysis (TGA) curves showed that the thermal stabilities of composites increased with longer ageing time, as did the values of the limited oxygen index (LOI). Meanwhile, the results of dynamic mechanical analysis (DMA) indicated that the glass transition temperature shifted to a higher temperature after ageing due to the effect of crosslinking, and both the crosslinking and degradation of PBT molecular chains act as the main factors in the whole process of thermo-oxidative ageing.

A phenethyl‐bridged DOPO derivative (DiDOPO) is combined with polytetrafluoroethylene (PTFE) in thermoplastic polyurethane (TPU). The flame retardancy and thermal stability of TPU/PTFE/DiDOPO composites with different weight percentages of DiDOPO are investigated by using limiting oxygen index (LOI), UL‐94 test, cone calorimetry test (CCT), scanning electronic microscopy (SEM), energy‐dispersive spectrometry, and thermogravimetric analysis (TGA). With the incorporation of 8 wt% DiDOPO, the LOI value of TPU/PTFE/DiDOPO composites increases to 34.0% from 25.4% of TPU, and the V‐0 rating level is achieved. The CCT results indicate that the peak heat release rate and total heat release of TPU/PTFE/DiDOPO composites decrease due to the addition of DiDOPO and PTFE. The thermal decomposition process of TPU is changed due to the present of DiDOPO and PTFE. Based on this, the Flynn–Wall–Ozawa method for the determination of characteristic degradation kinetics parameters is evaluated. SEM results and residues from TGA curves show that the addition of DiDOPO promotes the increase in the char layer and a crosslinked char coating exists after burning. The flame‐retardant mechanism is flame inhibition. Overall, these findings indicate that the combination of DiDOPO with PTFE in TPU is an effective way in developing high‐performance resins with attractive flame retardancy. POLYM. ENG. SCI., 59:1593–1602 2019. © 2019 Society of Plastics Engineers

In this work, the long glass fiber-reinforced polypropylene/red phosphorus (PP/LGF/RP) flame retardant composites were prepared by melting blend. The effects of thermo-oxidative aging on the mechanical properties, morphologies, and fire resistances of the PP/LGF/RP composites with different thermal exposure time at 1408C were investigated and discussed. The results showed that the crystallinity of PP in the PP/LGF/RP composites decreased and the mechanical properties decreased significantly with increasing the aging time. The scanning electronic microscopy photos indicated that the obvious reticular crack appeared on the surface of PP/LGF/RP composites and larger cracks appeared in local scope with an increase of aging time. The results from energy dispersive X-ray analysis (EDAX) proved that RP migrated from the inner to the surface of the composites. And the corresponding temperatures of maximum weight loss rate (T max ) of the PP/LGF/RP composites remained nearly unchanged, but the initial decomposition temperature (T 5% ) increased firstly, and then decreased. The flame retardant performances from the UL-94 tests, limiting oxygen index, and cone calorimeter test showed that the thermo-oxidative aging had a little effect on the flammability of the PP/LGF/RP composites. The thermal stability of PP/LGF/RP composites was improved slightly after thermo-oxidative aging. POLYM. COMPOS., 00:000-000, 2016. FIG. 5. Effect of thermo-oxidative aging on morphology of the impact fracture surfaces of PP/LGF/RP composites: (a) unaged, 3003; (b) 50 days aged, 3003; (c) unaged, 1,0003; and (d) 50 days aged, 1,0003. [Color figure can be viewed at wileyonlinelibrary.com]

Nanocomposites of organic nano-montmorillonite (nano-OMMT)-filled immiscible polyamide 6 (PA6)/polystyrene (PS) blends were prepared by three different processing methods. Masterbatch M1 of OMMT/PA6 and masterbatch M2 of OMMT/PS were prepared as separate masterbatchs by melt mixing with PA6 or PS, and then either mixed together or each mixed individually with appropriate amounts of PS or PA6, respectively. The effects of nano-OMMT content and processing method on the structure, phase morphology, and mechanical properties of the PA6/ PS/OMMT nanocomposites were investigated by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and mechanical properties tests. The results showed that the nano-OMMT by M1 and M2 masterbatches dispersed primarily as exfoliated platelets in the PA6 matrix in the final composites regardless of the method of preparation. A drastic decrease of dispersed PS phase size and a very homogeneous size distribution were observed with the addition of nano-OMMT. The PA6/ PS/OMMT nanocomposites prepared from the M2 displayed the smallest dispersed PS phase size and best distribution of OMMT. The improvement of the mechanical properties of the PA6/PS/OMMT nanocomposites was attributed to the enhanced compatibilization of the immiscible PA6/PS blends by using nano-OMMT. POLYM. ENG. SCI.,

In this work, modified expandable graphite (MEG) and zinc borate (ZB) are melt-blended with metal hydroxide/aluminum hydroxide flame retardant linear lowdensity polyethylene/ethylene vinyl acetate (LLDPE/ EVA) blends. The synergistic effects of MEG with ZB on the flammability, thermal stability and crystallization behaviors of LLDPE/EVA composites are characterized and discussed by UL-94 vertical burning, limiting oxygen index (LOI), thermogravimetric analysis, cone calorimeter test (CCT), carbon layer morphology, and differential scanning calorimetry (DSC). The addition of ZB and MEG apparently increases the LOI values and improves the UL-94 rating of the flame retardant LLDPE/EVA composites. The data obtained from the CCT indicate that the heat release rate, the total heat release and the gas production rate of the flame retardant LLDPE/EVA composites decrease remarkably with increasing the MEG content and the residues of the composites increase to 38.2% from 2.7% of the LLDPE/EVA blends, which indicates that MEG enhances the thermal stability and layer carbon capacity of the composites. The DSC results describe that MEG can act as a nucleating agent to accelerate the crystallization rate of the flame retardant composites, but the crystallinity of polypropylene of the flame-retardant composites firstly increases and then decreases with increasing the content of MEG. POLYM. COMPOS., 00:000-000,

In this work, the ethylene-propylene-diene monomer/polypropylene (EPDM/PP) thermoplastic elastomer filled with intumescent flame retardants (IFR) is fabricated by melting blend. The IFR are constituted with melamine phosphate-pentaerythritol (MP/PER) by compounding and reactive extruding, respectively. The effects of two kinds of MP/PER with different contents on the thermal stability, flame retardancy, and mechanical properties of materials are investigated by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94, cone calorimeter test (CCT), and scanning electron microscopy (SEM). FTIR results show that the reactive extruded MP/PER partly generates melamine pyrophosphate (MPP) compared with compound masterbatches. TGA data indicate that the best thermal stability is achieved when the molar ratio of MP/PER reaches 1.8. All the reactive samples show a higher flame retardancy than compound ones. The CCT results also exhibit the same trend as above in heat release and smoke production rate. The EPDM/PP composites filled with 30 and 35% reactive MP/PER exhibit the improved flame retardancy but become stiffer and more brittle. SEM photos display that better dispersion and smaller particle size are obtained for reactive samples.