Acetyl Tributyl

1050

Biomacromolecules 2008, 9, 1050–1057

Fabrication and Characterization of Poly(lactic acid)/Acetyl Tributyl Citrate/Carbon Black as Conductive Polymer Composites Jiugao Yu, Ning Wang, and Xiaofei Ma* School of Science, Tianjin University, Tianjin 300072, China Received November 20, 2007; Revised Manuscript Received January 15, 2008

By using acetyl tributyl citrate (ATBC) as the plasticizer of poly(lactic acid) (PLA) and carbon black (CB) as conductive filler, electrically conductive polymer composites (CPC) with different CB and ATBC contents were prepared. FTIR revealed that the interaction existed between PLA/ATBC matrix and CB filler and ATBC could improve this interaction. The rheology showed that ATBC could obviously decrease the shear viscosity and improve the fluidity of the composites but just the reverse for CB. With the increasing of CB contents, the enforcement effect, storage modulus, and glass-transition temperature increased but the elongation at break decreased. PLA/ ATBC/CB composites exhibited the low electrical percolation thresholds of 0.516, 1.20, 2.46, and 2.74 vol % CB at 30, 20, 10, and 0 wt % ATBC. The conductivity of the composite containing 3.98 vol % CB and 30 wt % ATBC reached 1.60 S/cm. Scanning electron microscopy revealed that the addition of ATBC facilitated the dispersion of the CB in the PLA matrix. Water vapor permeability (WVP) showed that, at the same CB contents, the more ATBC contents there were, the less the values of WVP were.

1. Introduction Conductive polymer composites (CPC) can be obtained by filling a polymer matrix with electrically conductive particles such as carbon black (CB), carbon nanotubes, graphite, metal powders, etc. CPC have a wide variety of potential applications such as self-regulated heating, positive temperature coefficient (PTC) materials,1 antistatic plastics,2 electromagnetic shielding,3 and environmentally sensitive membranes4 because of their resistivity change with mechanical, thermal, electrical, or chemical solicitations.5 Carbon black (CB) is the most widely used conductive filler for CPC.6 It is characteristic of polymers with CB that the electrical conductivity increases sharply at a critical filler concentration, called the percolation threshold, due to the formation of a conductive network throughout the polymer matrix. In addition to improvement of conductivity, CB can also improve the modulus and strength of the composites as the reinforced filler. As the matrices of CPC, polyolefins are widely applied because they provide good mechanical properties and chemical resistance and are readily processed by extrusion, injection molding, and compression molding. Currently, other matrices of CPC are also petroleum-based polymers such as poly(ethylene terephthalate),5 waterborne polyurethane,7 poly(carbonate),8 high impact polystyrene,9 and so on. Poly(lactic acid) (PLA) is a linear aliphatic polyester produced from annually renewable resources. PLA is synthesized by the ring-opening polymerization of lactides and lactic acid monomers,10–12 which are obtained from the fermentation of sugar feed stocks.13 PLA is well-known bioabsorbable material as tissue engineering scaffolds14 and biomedical applications (e.g., drug delivery and diagnosis).15 A shortage of petroleum resources and environmental concerns open a brighter perspective for PLA. It is a highly transparent and rigid material with a relatively low crystallization rate that makes it a promising * Corresponding author. E-mail: [email protected]. Fax: +86 22 27403475.

candidate for the fabrication of biaxially oriented films, thermoformed containers, and stretch-blown bottles.16 As a biodegradable polymer, it also gains attention as an alternative to conventional synthetic polymers in packaging applications.17 Undoubtedly, the combination of PLA with CB will broaden the novel application of both PLA and CPC. In this paper, CPC is prepared with admixing a small amount of CB content into a PLA matrix. To improve the flexibility of PLA, many chemicals, such as citric esters,18 poly(ethylene glycol), glucosemonoesters and partial fatty acid esters,19,20 have been tried to plasticize PLA. Acetyl tributyl citrate (ATBC),21 as a plasticizer of PLA, is blended with PLA to avoid its inherent brittle behavior. The influence of CB and ATBC contents on the physical properties of CPC is investigated in terms of the interaction between CB and PLA, rheology, mechanical properties, dynamic mechanical thermal analysis (DMTA), electrical properties, morphology, and water vapor permeability.

2. Experimental Section 2.1. Materials. Amorphous PLA was obtained from Natureworks LLC (United States). The general molecular weight average was about 160000–220000. The concentration of the D-(-)-isomer was 12.0 ( 1.0%. Corpren CB3000 was purchased from SPC, Sweden. This grade of CB had a DBP value of 380 cm3/100 g, an iodine adsorption of 1000 mg/g, and a mean particle size of 40 nm, as provided by the manufacturer. ATBC was purchased from Jinling Petrochemical Limited Corp., Sinopec Corp. 2.2. Preparation of CPC. CB fillers were mixed with ATBC and then added to PLA on twin-roller. The contents of ATBC were 0, 10, 20, and 30 wt % based on PLA. The composites were processed for 10 min with the twin-roller temperature at 125 °C. Then, the composites were pressed at 120 °C to obtain the sheet of CPC. 2.3. FTIR. FTIR spectra were obtained at 2 cm-1 resolution with BIO-RAD FTS3000 IR spectrum scanner. Typically, 64 scans were signal-averaged to reduce spectral noise. The samples were compressed to the sheet with the thickness of about 0.5 mm in the flat sulfuration machine, tested by attenuated total reflection measurements.

10.1021/bm7012857 CCC: $40.75  2008 American Chemical Society Published on Web 02/22/2008

Poly(lactic acid)/Acetyl Tributyl Citrate/Carbon Black

Biomacromolecules, Vol. 9, No. 3, 2008 1051

Figure 1. FTIR spectrum of CPCs with different ATBC and CB contents.

2.4. Rheology. Rheological measurements were performed on an XLY-II capillary rheometer (Jilin University Instrument Factory, Changchun, China) with a capillary diameter of 1 mm (L/D ) 40), no end corrections were applied. A series of displacement-time diagrams were obtained at predetermined temperatures and different pressure, and then it was transformed to shear stress-shear rate (τ-γ) and apparent viscosity-shear rate (η-γ) curves according to the following equation:

∆P · R 2L

(1)

4Q 3n + 1 · 4n πR3

(2)

η)τ⁄γ

(3)

τ) γ)

wherein L and R are capillary length and radius, ∆P is the pressure mounted on the long capillary extrusion of the melt (N/cm2), n is flow index depending on the temperature, and Q is the volume flux (cm3/s). 2.5. Mechanical Testing. The Testometric AX M350-10KN materials testing machine was operated and a crosshead speed of 50 mm/ min was used for tensile testing (ISO 1184-1983 standard). The data was averages of 5–8 specimens. 2.6. Dynamic Mechanical Thermal Analysis (DMTA). The DMTA using a Mark Netzsch DMA242 analyzer was performed on hot-pressed (5 MPa, 100 °C) thick specimens (40 mm × 7 mm × 2 mm) in a single cantilever bending mode at a frequency of 3.33 Hz and a strain ×2N, corresponding to a maximum displacement amplitude of 30 µm. The range of temperature was from -100 to 100 °C. The standard heating rate used was 3.0 °C min-1. 2.7. Electrical Conductivity. A model ZC36 electrometer (SPSIC Huguang Instruments and Power Supply Branch, China) was used for high resistivity samples with 50 mm diameter and 0.5 mm thickness. For more conductive samples (beyond 10-6 S/cm), sheets with dimensions of 30 mm × 5 mm and 0.5 mm thickness were measured

using a model ZL7 electrometer (SPSIC Huguang Instruments and Power Supply Branch, China) using a four-point test fixture. 2.8. Scanning Electron Microscope (SEM). The fracture surfaces of CPC were performed with a Philips XL-3 scanning electron microscope, operating at an acceleration voltage of 20 kV. CPC samples were cooled in liquid nitrogen and then broken. The fracture surfaces were vacuum-coated with gold for SEM testing. 2.9. Water Vapor Permeability (WVP). WVP tests were carried out by ASTM method E96 (1996) with some modifications.22 The membranes (about 0.5 mm thickness) were cut into circle shapes and sealed over with melted paraffin and stored in a desiccator at 20 °C. Relative humidity (RH) 0 was kept with anhydrous calcium chloride in the cell, and each cell was placed in a desiccator containing deionized water to provide a constant RH 100%. Water vapor transport was determined by the weight of the permeation cell. Changes in the weight of the cell were recorded as a function of time. Slopes were calculated by linear regression (weight changes vs time), and correlation coefficients for all reported data were >0.99. The water vapor transmission rate (WVTR) was defined as the slope (g/s) divided by the transfer area (m2). WVP (g m-1 s-1 Pa-1) was calculated as

WVP )

WVTR ·D P(R1 - R2)

(4)

where P is the saturation vapor pressure of water (Pa) at the temperature (20 °C), R1, the RH in the desiccator, R2, the RH in the permeation cell, and D is the membrane thickness (m). Under these conditions, the driving force [P(R1 - R2)] is 2338 Pa.

3. Results and Discussion 3.1. FTIR. The analysis of FTIR spectra of the composites enabled the interactions to be identified. If there were appreciable changes (e.g., band shifts, broadening) in the FTIR spectrum

1052 Biomacromolecules, Vol. 9, No. 3, 2008

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lactonic on the surface of CB,26 which could form the interaction with -CdO, -CH-O-, and -O-CdO groups of the PLA matrix. With the increase of ATBC content at each characteristic region, the wavenumber of the characteristic peak vs CB content plots basically located lower. It indicated that ATBC could decrease the wavenumber of the characteristic peak. According to the harmonic oscillator model, ATBC could improve the interaction between the PLA/ATBC matrix and CB particles. 3.2. Rheology. According to the power-law behavior,

τ ) Kγn

Figure 2. Effect of CB content on the wavenumber of specific characteristic peaks in FTIR spectrum of CPCs with different ATBC content.

of the composites with respect to the coaddition of each component, a distinct chemical interaction (hydrogen bonding or dipolar interaction) existed between the components.23 On the basis of the harmonic oscillator model, the reduction in force constant f could be represented by eq 5.24,25

∆f ) fb - fnb )

µ(V2b - V2nb) 4π2

(5)

where µ ) m1m2/(m1 + m2) corresponded to the reduced mass of the oscillator, υ the oscillating frequency, and f the force constant. The subscripts b and nb denote bonded and nonbonded oscillators, respectively. The reduction of force constant brought about by some interaction was directly related to the frequency (or wavenumber) shift of stretching vibrations. Thus, the lower the wavenumber corresponding to characteristic peak was, the stronger the interaction between the matrix and the filler was. Figure 1 showed the FTIR spectra of CPC at room temperature in several specific stretching regions. There were three FTIR spectra regions to identify the interaction in CPC. The first region appeared at 1749 cm-1, ascribed to the carbonyl (-CdO) characteristic stretching peak of PLA. The second one was ascribed to -C-O- bond stretching in the -CH-Ogroup of PLA at 1182 cm-1. The last region was composed of three characteristic peaks, ascribed to the -C-O- stretching vibration in the -O-CdO group at 1128, 1082, and 1043 cm-1, respectively. According to the data from Figure 1, the dependence of three characteristic regions on ATBC and CB contents was shown in Figure 2. The wavenumber of the characteristic peak vs CB content plots exhibited the similar behavior at three characteristic regions. With the increase of CB content in each PLA/ATBC composite, the characteristic peaks all shifted toward a lower wavenumber at three above-mentioned stretching regions. For PLA/ATBC (100/0) composite containing 5.34 vol % CB, the characteristic peaks respectively corresponding to the carbonyl bond, the -C-O- bond in the -CH-O- group, and the -C-O- bond in the -O-CdO group located at the wavenumbers of 1740, 1173, and 1070 cm-1, about 9, 9, and 12 cm-1 lower than that for pure PLA, respectively. These shifts of stretching absorption to lower wavenumber were ascribed to the interaction between PLA matrix and CB. There were many functional polar groups like carboxylic, phenolic, and

(6)

where τ is shear stress, γ is shear rate at the capillary wall, K is consistency of the materials depending on the temperature, the structure, and the formulation of the polymer. Substituting eq 6 for τ in the relationship of eq 3 between τ and γ yielded:

η ) Kγn-1 logη ) logK - (1 - n)logγ

(7) (8)

According to Arrhenius equation:

η ) A · e∆Eη⁄RT logη ) logA + ∆Eη ⁄ (RT · ln10)

(9) (10)

where ∆Eη is the vicious flow activation energy, A is the consistency related to structure and formulation, and R is the gas constant 8.314 J mol-1 K-1. Double logarithmic plots of the η-γ curves were shown in Figure 3. All composites showed shear-thinning behavior, which was mainly ascribed to the gradual reduction of the intermolecular bonding of the PLA/ATBC matrix. As shown in Figure 3, both ATBC content and CB content largely influenced the rheological behavior of the composites. The apparent viscosity η of PLA/ATBC/CB composites decreased with the increasing of ATBC contents and with the decreasing of CB contents. According to eq 8, linear fit equations related to log η and log γ indicated that the slope of the linear fit equation was -(1 - n) and the intercept log K. The flow index n and log K at 110, 120, and 130 °C were listed in Table 1. ATBC obviously decreased the shear viscosity and improve the fluidity of the composites, but just the reverse for CB. The flow index n decreased with the increasing of CB content, or with the decreasing of ATBC contents, which meant that the introduction of CB made the composites more sensitive to the shear rate, while the composites with high ATBC contents were less sensitive to the shear rate. The effect of CB and ATBC contents on log K was opposite to the flow index n. It indicated that CB could form strong bonding interactions with PLA and block the slippage movement among PLA molecules, while as the plasticizer of PLA, ATBC weakened the intermolecular interactions of PLA and facilitated the slippage movement. According to eq 10, log η (x ) 0) ∼ 1/T curves were linearized to calculate ∆Eη from the slope (∆Eη/R ln 10). The vicious flow activation energy ∆Eη represented the effect of the temperature on the behavior of the composites. The higher ∆Eη was, the more the temperature-sensitive behavior of the composite was. According to the values of ∆Eη (x ) 0) in Table 1, the composite was less sensitive to processing temperature when ATBC content increased or CB content decreased. 3.3. Mechanical Properties. Figure 4 showed the effect of CB and ATBC contents on mechanical properties of PLA/ ATBC/CB composites. As the plasticizer of PLA, ATBC



Figure 3. Rheology curves of PLA/ATBC/CB composites with different ATBC and CB contents at 110, 120, and 130 °C. Table 1. Flow Index n, log K, and Vicious Flow Activation Energy ∆Eη (X ) 0) of PLA /ATBC/CB Composites at 110, 120, and 130 °C.

CB contents (vol %) PLA/ATBC 0 1.39 3.41 PLA/ATBC 0 1.24 3.05 PLA/ATBC 0 1.2 2.76 PLA/ATBC 0 0.516 2.53

110 °C

120 °C

130 °C

n

n

n

log K

log K

∆Eη log K KJ/mol

(100/0) 0.36 5.57 0.40 5.28 0.47 5.03 79.87 0.31 6.59 0.38 6.26 0.42 5.78 92.40 0.26 6.99 0.31 6.67 0.37 6.35 119.55 (100/10) 0.49 4.69 0.51 4.47 0.56 4.10 75.25 0.44 5.60 0.48 5.36 0.52 5.15 83.47 0.38 6.25 0.43 6.04 0.47 5.81 100.25 (100/20) 0.56 4.33 0.60 4.05 0.64 3.80 0.46 5.44 0.50 5.20 0.54 4.97 0.42 6.10 0.46 5.84 0.50 5.57

68.18 75.49 85.81

0.63 4.02 0.66 3.79 0.68 4.39 0.54 5.02 0.58 4.79 0.62 4.42 0.47 5.85 0.50 5.56 0.52 5.24

60.71 64.39 77.35

(100/30)

decreased the tensile strength but increased the elongation at break of the composites. With the increasing of ATBC contents, the curves of tensile strength vs CB contents moved down, while the curves of elongation at break vs CB contents moved up. As the filler of PLA/ATBC matrix, CB had an obvious enforcement effect, which increased the tensile strength but decreased the elongation at break of the composites with the increasing of CB contents. Interfacial interaction between the fillers and matrix was an important factor affecting the mechanical properties of the

composites. Thus, theoretical tensile yield strength of the composites were modeled for the cases of adhesion and no adhesion between the filler particles and matrix. In the case of no adhesion, the interfacial layer could not transfer stress. The tensile strengths of the composites could be predicted using Nicholais-Narkis models27

σc ) σm(1 - aφb)

(11)

where φ, σc and σm were volume fraction of filler, and tensile yield strengths of the composite and matrix, respectively. In the Nicholais and Narkis model, parameters a and b were the constants related to filler-matrix interaction and geometry of the filler, respectively. The value of a less than 1.21 represented good adhesion for composites containing spherical fillers. In the absence of adhesion for the composites, eq 11 became

σc ⁄ σm ) (1 - 1.21φ2⁄3)

(12)

This model was based on the assumption that the decrease of tensile yield strength was due to the reduction in effective crosssection area caused by the spherical filler particles. If perfect adhesion were present between the matrix and CB particles, the loading stresses would be transferred to CB and no reduction in effective surface area would result. The experimental and theoretical curves were plotted in Figure 5. It could be seen that the experimental value of PLA/ ATBC/CB composite was much higher than that calculated by the eq 12. This indicated that there was the adhesion between the PLA/ATBC matrix and CB particles, and with the increasing


Yu et al.

Figure 4. Effect of CB contents on the mechanical properties of CPC.

Figure 6. Effect of CB and ATBC contents on storage modulous of the composites. Figure 5. Effect of CB volume fraction on yield stress ratio of the composite and matrix.

of ATBC contents, the experimental curves of the composites were elevated. It was indicted that ATBC improved the interaction between the PLA matrix and CB particles. It was correspondent with the result of FTIR. 3.4. Dynamic Mechanical Thermal Analysis (DMTA). The behavior of storage modulus for the composite with different ATBC or CB contents was shown in Figure 6. It was known that storage modulus detected by DMTA was related to the stiffness. The stiffness of composites was increased with the increasing of CB contents. This improvement was possibly associated with the interaction between PLA/ATBC matrix and CB. However, the introduction of ATBC decreased the storage modulus of the composites because ATBC as the plasticizer actually reduced the stiffness of PLA/ATBC matrix. In DMTA testing, the storage modulus kept almost the same below glass-transition temperature Tg then decreased abruptly where the region was contributed to the glass transition. In the curves of loss factor (tan δ) as a function of temperature, the peaks were related to the glass-transition temperature. The effect of CB and ATBC contents on the curves of tan δ versus temperature was showed in Figure 7. As the plasticizer, ATBC increased the free volume and reduced the glass transitions of composites. As the physical joint, CB improved the intermolecular interaction of PLA, which brought adjacent chains of PLA close and hence reduced the free volume and raised the glass transitions of composites. In addition, the tan δ peak for

Figure 7. Effect of CB and ATBC contents on the curves of tan δ vs temperature.

the composite containing high ATBC content (30 wt %) is broad in comparison with the other composite containing low ATBC content (0, 10, and 20 wt %), probably indicating that excessive ATBC could not completely combine with PLA and form the multiphase. 3.5. Electrical Conductivity. Figure 8 showed the effect of ATBC and CB contents on electrical conductivity of CPC. It was similar to the characteristic of polymers with conductive fillers that the electrical conductivity increased with increasing



Figure 8. Electrical conductivity of CPC with different CB and ATBC contents. Table 2. Some Parameters Related to the Electrical Conductivity of Four PLA/ATBC/CB Composites PLA/ATBC composites

percolation threshold (vol %)

exponent (t)

correlation coefficients (R)

log σo

100/0 100/10 100/20 100/30

2.74 2.46 1.20 0.516

1.66 1.77 1.92 3.41

0.982 0.965 0.980 0.986

2.33 3.06 3.80 6.71

the content of CB, increased sharply at a critical CB concentration, and tended to level off above the critical CB concentration. At the same CB contents, the conductivity of CPC was raised with the increasing of ATBC contents from 0 to 30 wt %. The critical concentration was usually interpreted as the percolation threshold required to form the interconnecting conductive networks in the polymer matrix. From these curves, the percolation could be also estimated, which were listed in Table 2. At the CB percolation level, the conductance of the composite was approximately increased by 8–11 orders of magnitude. With the increasing of ATBC contents from 0 to 30 wt %, a considerable reduction in percolation threshold was observed from 2.74 to 0.516 vol %. In general, the higher the content of ATBC was, the lower the percolation threshold of the composite was. It demonstrated the superiority of ATBC to the conductance of the composite. The lower percolation threshold was attributed to the fine contact of the matrix with CB particles being distributed in the composite in the presence of ATBC. Because the excessive ATBC (30 wt %) could form its own phase domains, it had a synergistic effect on the formation of a conductive network along with CB. However, for the composite containing no ATBC, a perfect conductive network was hard to be constructed and a high percolation threshold was obtained. In “universal percolation theory”,28 eq 13 related the conductivity (σ) of a polymer filled with conductive particles to the volume fraction (φ) of the particles in the composites above the percolation threshold (φc).

σ ) σ0(φ - φc)t

(13)

where σ0 was a constant that was typically assigned to the plateau conductivity of the fully loaded composite and the exponent (t) was used to interpret the mechanism of network formation. Generally, the t was about 1.1–1.3 for a twodimensional system, while a higher value, in the range from 1.6 to 2.0, was for a three-dimensional system.

Figure 9. Electrical conductivity as a function of excess concentration (φ - φc) for electrically conductive in CPC.

The t value could be obtained from the slope of the line in a log(φ - φc) vs σ plot in Figure 9. Some parameters were estimated from the experimental data and eq 13, as shown in Table 2. The log(φ - φc) vs σ plots of four PLA/ATBC composites exhibited a good linearity (R > 0.96). The t value and log σ0 improved with the increasing of ATBC contents. The t values for the composites containing below 20 wt % ATBC were in the range from 1.6 to 2.0, indicating that the three-dimensional conductive networks were formed. However, the t value for PLA/ATBC (100/30) composite was 3.41, larger than the value predicted from the universal percolation theory. As the plasticizer of PLA, ATBC could form the homogeneous phase with PLA at the low ATBC contents. However, ATBC could not completely combine with PLA and form its own phase at the excessive ATBC contents (e.g., PLA/ATBC 100/30). CB could be distributed in both PLA/ATBC composite and ATBC phase. Therefore, the high exponent t for PLA/ATBC (100/30) composite could be attributed to the multipercolation.29 It was consistent with DMTA. As shown in Figure 7, the span of transition temperature for PLA/ATBC (100/30) composites was much larger than the other. It could be related to glass transition of the multiphase. At the same time, the σ0 for the composite containing high ATBC content (30 wt %) is higher than those with the low ATBC contents. It further suggested that the separated ATBC phase domains could contribute to the formation of conductive network. 3.6. Morphology. Figure 10 shows SEM micrographs for PLA/ATBC/CB composites with different ATBC contents, respectively. As shown in Figure 10a, the macroagglomerates of CB particles were located in the PLA phase (no ATBC) like the islands in the sea without the connection. Although there were the interactions between CB and PLA, it was not enough to disperse CB well in the PLA phase. A mass of CB was needed to form the electrical conductance network. It indicated that the composite without ATBC had the higher percolation threshold. When ATBC was added to PLA, both the low processing viscosity (as revealed by rheology) and the strong interaction (as proved by FTIR) between CB and the matrix were propitious to the dispersion of CB. Compared to dispersion in Figure 10a, ATBC could decrease the size of CB agglomerates, shown in Figure 10b,c,d, and the excessive ATBC (30 wt %) could form its own phase domains, which was beneficial to the formation of conductive network along with CB. The appropriate CB agglomerates were developed to contact together and form


Yu et al.

Figure 10. SEM micrographs of cryofractured PLA/ATBC/CB composites: (a) PLA/ATBC (100/0) with 1.39 vol % CB, (b) PLA/ATBC (100/10) with 2.46 vol % CB, (c) PLA/ATBC (100/20) with 1.2 vol % CB, and (d) PLA/ATBC (100/30) with 2.03 vol % CB.

30 wt %), while WVP values decreased obviously for the composites with low ATBC contents (0 and 10 wt %). Water resistance of CB was better than PLA/ATBC matrix. The addition of CB probably introduced a tortuous path for water molecule to pass through.30 At the high ATBC contents, CB particles could disperse well in the matrix. There were few paths for water molecule to pass through at the low CB contents, so the increasing of CB had little effect on the decreasing of WVP and vice versa.

4. Conclusion

Figure 11. Effect of CB and ATBC contents on water vapor permeability of the composites.

random networks. Therefore, ATBC could decrease the percolation threshold of CB. It was consistent with the results of electrical conductivity. 3.7. Water Vapor Permeability. Water vapor permeability (WVP) was used to study the moisture transport through the film. As shown in Figure 11, WVP in CPC composites with different ATBC contents had the similar trend with the increasing of CB contents. Water vapor easily went through PLA film with the highest WVP values of 1.45 × 10-10 g m-1 s-1 Pa-1. At the same CB contents, the more ATBC contents there were, the less the values of WVP were due to the moisture barrier of hydrophobic ATBC. With the increasing of CB contents, WVP values decreased gradually for the composites with high ATBC contents (20 and

In this paper, PLA/ATBC/CB composites were prepared as potential CPC. ATBC could improve the interaction between the PLA/ATBC matrix and CB particles, revealed by FTIR and the dependence of tensile yield strength on the CB and ATBC contents with the aid of Nicholais-Narkis models. Both this strong interaction and the low processing viscosity (as showed by rheology) were propitious to decrease the size of CB agglomerates (as showed by SEM) when ATBC was added. The appropriate CB agglomerates were developed to contact together and form random networks, therefore, ATBC could decrease the percolation threshold of CB. When ATBC contents were increased from 0 to 30 wt %, the percolation threshold of CB decreased from 2.74 to 0.516 vol %. According to universal percolation theory, the three-dimensional conductive networks were formed in PLA/ATBC/CB composites with below 20 wt % ATBC. The 30 wt % ATBC could not completely combine with PLA and form the multiphase, which was beneficial to the formation of conductive network along with CB. The introduction of CB can improve the storage modulus and the glass-transition temperature of the composites, but the reverse for ATBC. CB could resist water vapor to penetrate the composites and at the same CB contents, the more ATBC contents there were, the less the values of WVP were.


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Acetyl Tributyl

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