Influence of graphene nanoplatelet incorporation and dispersion state on thermal, mechanical and electrical properties of biodegradable matrices

doi:10.1016/j.jmst.2017.10.013

Abstract

Abstract:

Graphene nanoplatelets (GNPs) were used as multifunctional nanofiller to enhance thermal and mechanical properties as well as electrical conductivity of two different biodegradable thermoplastics: poly lactide (PLA) and poly (butylene adipate-co-terephthalate) (PBAT). Morphological investigations showed different levels of GNP dispersion in the two matrices, and consequently physical properties of the two systems exhibited dissimilar behaviours with GNP incorporation. Crystallinity of PLA, determined from differential scanning calorimetry, was observed to increase markedly with addition of GNPs in contrast to the decrease in crystallinity of PBAT. Isothermal and non-isothermal thermogravimetric analyses also revealed a more significant delay in thermal decomposition of PLA upon addition of GNPs compared to that of PBAT. Furthermore, results showed that increasing GNP content of PLA and PBAT nanocomposites influenced their Young’s modulus and electrical conductivity in different ways. Modulus of PBAT increased continuously with increasing GNP loading while that of PLA reached a maximum at 9 wt% GNPs and then decreased. Moreover, despite the higher conductivity of pure PBAT compared to pure PLA, conductivity of PLA/GNP nanocomposites overtook that of PBAT/GNP nanocomposites above a certain GNP concentration. This demonstrated the determining effect of nanoplatelets dispersion state on the matrices properties.

Key words: Graphene, Nanocomposite, Poly lactide, Poly butylene adipate-co-terephthalate, Thermal stability, Electrical conductivity, Properties

Sima Kashi, Rahul K. Gupta, Nhol Kao, S. Ali Hadigheh, Sati N. Bhattacharya. Influence of graphene nanoplatelet incorporation and dispersion state on thermal, mechanical and electrical properties of biodegradable matrices[J]. J. Mater. Sci. Technol., 2018, 34(6): 1026-1034.

Figures/Tables 12

Table 1 Thermal properties of PLA/GNP and PBAT/GNP nanocomposites obtained from DSC measurements with cooling and heating rates of 2 °C/min.

Sample	Cooling cycle			Second heating cycle
	T_c (°C)	ΔH_c (J/g)	X_c (%)	T_g (°C)	T_m (°C)	ΔH_m(J/g)	X_c (%)
PL0	99	16.3	17.4	59	169	33.9	29.6
PL3	108	30.6	33.7	61	170	32.8	36.0
PL6	107	30.1	34.2	61	170	33.4	37.9
PL9	110	30.6	35.9	60	171	32.9	38.6
PL12	112	31.3	37.9	59	171	32.4	39.3
PL15	116	31.0	38.9	60	171	33.4	41.9
PB0	86	8.2	7.2	-34	123	12.2	10.7
PB3	98	6.5	5.9	-34	128	8.7	7.9
PB6	100	5.3	4.9	-35	128	8.2	7.7
PB9	102	5.6	5.4	-35	129	6.6	6.4
PB12	104	5.2	5.2	-34	128	5.9	5.9
PB15	105	4.7	4.9	-34	127	5.0	5.1

Fig 1. SEM images of (a) PB3, (b) PB6, (c) PB9, (d) PL3, (e) PL6, and (f) PL9 nanocomposites.

Fig. 2. X-ray diffraction pattern of GNPs.

Fig. 3. X-ray diffraction patterns of (a) PLA/GNP and (b) PBAT/GNP nanocomposites.

Fig. 4. Absolute and normalised crystallization temperatures of (a) PLA/GNP and (b) PBAT/GNP nanocomposites. Absolute and normalised degrees of crystallinity of (c) PLA/GNP and (d) PBAT/GNP nanocomposites, obtained from cooling cycles.

Fig. 5. Comparative MDSC thermograms of (a) PLA/GNP and (b) PBAT/GNP nanocomposites during the second heating cycles.

Fig. 6. TGA curves of (a) PLA/GNP and (b) PBAT/GNP nanocomposites in nitrogen at heating rate of 10 °C/min.

Table 2 TGA: Temperatures at which 5, 10 and 50% of initial weight of nanocomposites are degraded.

PLA/GNP Nanocomposites				PBAT/GNP Nanocomposites
Sample	T_5% (°C)	T_10% (°C)	T_50% (°C)	Sample	T_5% (°C)	T_10% (°C)	T_50% (°C)
PL0	325.9	338.8	355.7	PB0	369.2	378.6	400.3
PL3	333.9	339.9	357.0	PB3	368.1	377.1	399.9
PL6	334.9	339.8	355.0	PB6	369.6	378.3	400.4
PL9	337.1	342.5	357.6	PB9	371.8	380.5	403.6
PL12	337.4	343.6	359.2	PB12	373.8	383.2	405.1
PL15	339.6	345.3	362.2	PB15	374.3	383.7	407.8

Table 3 TGA: Temperatures at which 5, 10 and 50% weight reduction occurs in the initial polymer content of the nanocomposites.

PLA/GNP Nanocomposites				PBAT/GNP Nanocomposites
Sample	T_5% (°C)	T_10% (°C)	T_50% (°C)	Sample	T_5% (°C)	T_10% (°C)	T_50% (°C)
PL0	325.9	338.8	355.7	PB0	369.2	378.6	400.3
PL3	333.7	339.8	356.8	PB3	367.7	376.7	399.3
PL6	334.4	339.4	354.1	PB6	368.9	377.8	399.4
PL9	336.4	341.8	356.4	PB9	370.7	378.9	401.8
PL12	336.3	342.5	357.6	PB12	372.0	381.5	402.8
PL15	338.2	344.0	359.7	PB15	371.9	381.5	404.1

Fig. 7. (a) Isothermal TGA analysis at 265 °C for 5 h in air; (b) Temperature scans with a 5-h isothermal step at 265 °C in air and heating rate of 20 °C/min.

Fig. 8. Absolute and normalised Young’s moduli of (a) PLA/GNP and (b) PBAT/GNP nanocomposites.

Fig. 9. Electrical conductivity of PLA/GNP and PBAT/GNP nanocomposites versus GNP loading.

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