A flame-retardant polylactic acid composite added with piperazine pyrophosphate and melamine cyanurate was developed. Piperazine pyrophosphate and melamine cyanurate showed synergistic effect in the polylactic acid composites. When the weight ratio of piperazine pyrophosphate to melamine cyanurate was 4:1 and the loading of the piperazine pyrophosphate/melamine cyanurate flame retardant was 15 wt.%, the prepared polylactic acid composites passed V-0 rating in the UL-94 test and achieved the high limit oxygen index value of 34.9%. The cone calorimeter test result confirmed that the addition of piperazine pyrophosphate/melamine cyanurate flame retardant reduced the total heat release value of polylactic acid. The effect of polylactic acid biodegradation on the flame retardancy of polylactic acid composite was further discussed. The biodegraded polylactic acid, which was exposed to the air for 8 months, showed high flame retardancy and even passed V-0 rating in the UL-94 test without the addition of piperazine pyrophosphate/melamine cyanurate flame retardant, which proved that biodegradation could affect the flame retardancy of polylactic acid.

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In this study, a magnesium phosphate whisker (DPM-H) was synthesized by the acid-base neutralization reaction between magnesium hydroxide and 10-hydroxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-OH) at 120 C. A new synergistic intumescent flame retardant (IFR) for epoxy resin (EP), which was composed of DPM-H and ammonium polyphosphate (APP) was thoroughly studied. When the IFR loading was 8%, with the DPM-H to APP weight ratio at 1:7, the prepared flame-retardant EP (EPDA-2) passed the vertical burning tests (UL-94) V-0 rating and obtained the limiting oxygen index (LOI) value of 29.3%. Microscale combustion calorimetry (MCC) results showed that the total heat release (THR) of EPDA-2 reduced by 32.1% compared with pure EP. Meanwhile, the addition of DPM-H can partially solve the problem of the decrease of the EP mechanical property caused by the addition of APP. Compared with the flame-retardant EP with the 8% loading of APP, the impact strength of EPDA-2 increased 152.3%.

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The degree of the imidization reaction determines the properties of polyimide (PI) obtained by the thermal curing process. In this paper, amine-modified graphene (N-GO) was designed by integrating pyridine structure with graphene and acting as a catalyst to promote the imidization reaction of PI. Fouriertransform infrared spectroscopy (FTIR), scanning electron microscope (SEM) were then used to confirm the morphology and structure of N-GO. The catalytic effect of N-GO in imidization reaction was obtained by FTIR and subsequently characterized by differential scanning calorimetry (DSC) and water contact angle (WCA). Surprising results suggest that the agglomeration of N-GO can also contribute to solid-phase reactions in imidization reactions.Lastly, the results of mechanical property tests, thermogravimetric analysis (TGA), and FTIR demonstrated that the composite films showed excellent tensile strength (176.2 MPa) and thermal stability (513.0 C); at the same content, only 0.5% of N-GO addition reduced the imidization temperature by 20 C, exhibiting remarkable enhancement effects. This research is a valuable solution to the problem in performance caused by low-temperature curing agent residues in films, and it is expected to be used in the microelectronics field.