Effect of Phosphite⁃Functionalized Polysilsesquioxane on Flame Retardancy of Polylactic Acid

doi:10.19491/j.issn.1001-9278.2020.06.002

Abstract

Abstract:

The chain?extended PLA was prepared by blending PLA with poly(amino?epoxy) silsesquioxane (PSQ), and phosphate?functionalized poly(amino?epoxy) silsesquioxane (PPSQ). The effect of phosphite ester groups on the chain extension and flame retardancy of PSQ in PLA matrix was investigated, and the flame retardant mechanism of PPSQ was further studied in detail. The results showed that the PPSQ significantly improved the molecular weight and complex viscosity of PLA in comparison of PSQ, indicating that the PLA?PPSQ compound achieved a better chain?extension effect. The incorporation of PPSQ also enhanced the flame retardancy of PLA and led to a limiting oxygen index of 25.4 vol% for the chain?extended PLA, which increased by 31.6 % compared to pure PLA. Furthermore, the heat release rate and total heat release of PLA?PPSQ compound also decrease by 18.1 % and 16.6 %, respectively. On the basis of the flame retardant mechanism, the introduction of phosphite ester groups into PSQ can promote the migration of silicon to the surface during the combustion of PLA?PPSQ compound and forms a dense carbon layer rich in silicon carbide and silicon oxide. Such a carbon layer can effectively inhibit the transfer of heat and oxygen and endows PLA with excellent flame retardancy accordingly.

Key words: polylactic acid, phosphite, polysilsesquioxane, chain extension, flame retardancy, mechanism

CLC Number:

TQ323.6

Juan LIANG, Zewen JIANG, Weiguang GONG, Xin MENG. Effect of Phosphite⁃Functionalized Polysilsesquioxane on Flame Retardancy of Polylactic Acid[J]. China Plastics, 2020, 34(6): 7-13.

Figures/Tables 10

Fig. 1. Chemical structure of PPSQ

Fig. 2. Chain?extending mechanism of PPSQ on PLA

样品	分子量/kg·mol^-1
PLA	141.4±3.1
PLA?PSQ	152.5±2.6
PLA?PPSQ	170.1±3.5

Tab. 1. Molecular weight of PLA, PLA?PSQ and PLA?PPSQ

Fig. 3. Complex viscosity of PLA, PLA?PSQ and PLA?PPSQ versus time

样品

极限氧指数/%

PLA

PLA?PSQ

PLA?PPSQ

19.3

23.6

25.4

Tab. 2. Limiting oxygen index of PLA, PLA?PSQ and PLA?PPSQ

Fig. 4. Cone calorimetry curves of PLA, PLA?PSQ and PLA?PPSQ

样品	PHRR/kW·m^-2	THR/MJ·m^-2	残炭量/%
PLA	461.1	78.5	3.3
PLA?PSQ	422.3	69.5	11.3
PLA?PPSQ	377.5	65.5	24.3

Tab. 3. Cone calorimetry results of PLA, PLA?PSQ and PLA?PPSQ

Fig. 5. SEM micrographs of surfaces residues of PLA, PLA?PSQ and PLA?PPSQ after cone calorimetry test

Fig. 6. FTIR spectra of PLA, PLA?PSQ and PLA?PPSQ after cone calorimetry test

32.7

42.4

PLA?PPSQ

1.70

1.40

Tab. 4. EDS and ICP results of chain?extended PLA after cone calorimetry test

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