For preparing good performance polymer materials, poly(trimethylene terephthalate)/CaCO3 nanocomposites were prepared and their morphology, rheological behavior, mechanical properties, heat distortion, and crystallization behaviors were investigated by transmission electron microscopy, capillary rheometer, universal testing machine, impact tester, heat distortion temperature tester, and differential scanning calorimetry (DSC), respectively. The results suggest that the nano-CaCO3 particles are dispersed uniformly in the polymer matrix. PTT/CaCO3 nanocomposites are pseudoplastic fluids, and the CaCO3 nanoparticles serve as a lubricant by decreasing the apparent viscosity of the nanocomposites; however, both the apparent viscosity and the pseudoplasticity of the nanocomposites increase with increasing CaCO3 contents. The nanoparticles also have nucleation effects on PTT’s crystallization by increasing the crystallization rate and temperature; however, excessive nanoparticles will depress this effect because of the agglomeration of the particles. The mechanical properties suggest that the CaCO3 nanoparticles have good effects on improving the impact strength and tensile strength with proper content of fillers. The nanofillers can greatly increase the heat distortion property of the nanocomposites.
Poly(trimethylene terephthalate) (PTT), as shown in Scheme
Molecular formula of PTT.
Inorganic particulate nanofillers have been employed to improve the properties and/or lower costs of the polymer products. Generally, nanosized fillers are superior to their micron-sized counterparts in improving the mechanical and thermal properties of thermoplastics because of their larger interfacial area between the particles and the surrounding polymer matrix [
In the present work, in order to improve the mechanical and thermal properties of the PTT, PTT/CaCO3 nanocomposites were prepared by melt blending and characterized in terms of their morphology, rheological behavior, mechanical properties, heat distortion temperature, crystallization, and subsequent melting behaviors by various experimental measurements. The tri(dioctylpyrophosphateoxy) titanate was used as a modifier to treat CaCO3 to avoid the agglomeration.
PTT homopolymer was supplied in pellet form by Shell Chemicals (USA) with weight-average molecular masses (
PTT was dried in a vacuum oven at 120°C for 12 h before preparing the blends. The dried PTT pellets and the modified CaCO3 nanoparticles were mixed together with different weight ratios of PTT/CaCO3 as follows: C0: 100/0; C1: 99/1; C2: 98/2; C4: 96/4; C6: 94/6; C8: 92/8; C20: 80/20; C30: 70/30; the mixture were melt-blended for 10 min in a high-speed mixer and then transferred to a ZSK-25WLE type twin-screw extruder (WP Co. Germany) with five heating cells, operating at a screw speed of 100 rpm and with temperatures of 210, 235, 250, 255, 255, and 250°C from the first cell to the die. The resultant blend ribbons were cooled in cold water, cut into pellets, and redried before being used in measurements.
The dispersion state of the nano-CaCO3 particles in the polymer matrix was examined with a Hitachi 900 transmission electron microscopy (TEM, Hitachi, Japan) at an accelerating voltage of 10 kV.
The rheological behaviors of different PTT/CaCO3 nanocomposites were determined with an XLY-II type capillary rheometer (Jilin University Sci. & Edu. Instrument Co., China) equipped with the capillary length of 40 mm and the diameter of 1 mm. The sample weights were about 1.5 g, and the specific temperatures were set from 235 to 250°C with the shearing stress in the range of 18–129 kPa. The samples were added into the capillary and then heated to specific temperature, held for 10 min, and then their rheological behaviors were tested at different stress.
The normative splines used in mechanical properties testing were all prepared by a microinjection molding machine (SZ-15, Wuhan Ruiming Machinery, China) at the cylinder temperature of 255°C and mold temperature of 20°C. The tensile strength testing was done according to the ISO 3167-2002/A standard on the computer controlled electronic universal material machine (WSM20, Changchun Intelligent Sci. & Techn. Co. Ltd., China). The impact tests were carried out according to the ISO 179-1982 standard using a Charpy impact tester (JJ-5.5, Changchun Intelligent Instrument Co. Ltd., China) with unnotched type sample; the data reported were the mean and standard deviation from five determinations.
The melt-crystallization and subsequent melting behaviors of the various nanocomposites were performed on a differential scanning calorimetry (Diamond DSC, Perkin-Elmer Co., USA) and the weight of samples were approximately 7.0 mg. The dried samples were heated to 260°C at 80°C/min under a nitrogen atmosphere, held for 5 min to release the thermal history, and then cooled to 50°C at a constant cooling rate of 10°C/min, held for 3 min, and finally heated again to 260°C at a rate of 10°C/min; the first cooling and subsequent melting processes were recorded.
The heat distortion temperatures (
The micrographs of C1, C2, C4, and C8 performed on TEM are shown in Figure
Transmission electron micrographs of nanocomposites C1, C2, C4, and C8.
The influences of nano-CaCO3 contents on the mechanical properties of different nanocomposites are shown in Table
Mechanical properties and heat distortion temperatures of different PTT/CaCO3 nanocomposites.
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C0 |
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C1 |
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C2 |
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C4 |
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C8 |
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C20 |
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C30 |
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a: tensile strength.
b: elastic modulus.
c: breaking elongation.
d: impact strength.
The heat distortion temperatures (
The length-diameter ratio of the capillary used in this test is 40 : 1, so the melt flow in this capillary can be seen as steady state flow when the shearing stress is small, ignoring the end effect. The apparent viscosity of the melt is calculated by the Hagen-Poiseuille equation [
Relationship between the apparent viscosity and shearing rate of the various PTT/CaCO3 nanocomposites.
Although the various nanocomposites have the similar rheological curves with increasing shearing rate, their apparent viscosity are quite different with increasing CaCO3 contents. Chen et al. [
The melt’s non-Newtonian fluid index,
We can get the
Relationship between
The relationships between
Relationship between
The dependence of
The
Relationship between
The DSC melt-crystallization curves for different PTT/CaCO3 nanocomposites are shown in Figure
DSC parameters of different PTT/CaCO3 nanocomposites.
Sample | Cooling process | Heating process | |||||
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C0 | 177.6 | — | 10.91 | −50.5 | — | 224.9 | 65.9 |
C1 | 185.1 | — | 6.97 | −51.9 | 214.4 | 229.6 | 57.2 |
C2 | 181.2 | — | 6.73 | −48.2 | 210.1 | 229.7 | 59.9 |
C4 | 181.7 | — | 7.64 | −51.7 | 211.1 | 228.5 | 59.2 |
C6 | 183.4 | — | 8.19 | −52.4 | 211.4 | 227.8 | 56.5 |
C8 | 184.3 | 180.6 | 9.94 | −50.9 | 213.0 | 230.1 | 56.6 |
C20 | 187.6 | 180.8 | 12.37 | −56.1 | 214.1 | 229.1 | 59.1 |
C30 | 186.7 | 180.9 | 9.75 | −51.1 | 213.1 | 227.7 | 52.7 |
DSC melt-crystallization curves for different PTT/CaCO3 nanocomposites.
The subsequent melting DSC curves of the above samples are shown in Figure
DSC melting curves for different PTT/CaCO3 nanocomposites.
It can also be seen from the Table
PTT/CaCO3 nanocomposites’ melt belongs to the pseudoplastic fluid, and the pseudoplasticity increases with the increasing CaCO3 content. The CaCO3 nanoparticles serve as a lubricant in the nanocomposites that decrease the melt apparent viscosity obviously with only 1% content; however, the melt viscosity increases gradually with increasing CaCO3 content from 1% to 30%. When the concentration of CaCO3 is below 4%, the nanoparticles disperse uniformly in the matrix. The CaCO3 nanoparticles act as nucleus for the melt-crystallization of the nanocomposites, and it increases the start-crystallization temperature and the crystallization rate of the nanocomposites although large content of CaCO3 particles will depress the nucleation effect. The CaCO3 nanocomposites also have both reinforcement and toughening effects on the PTT matrix, in which 2–8% contents of CaCO3 nanoparticles are preferred for improving both the impact strength and the tensile strength. The CaCO3 particles have good effect on improving the thermal resistance of PTT.
The work is supported by the financial support from the Natural Science Foundation of Hebei Province (B2010000219) and the Undergraduate Science and Technology Innovation Foundation of Hebei University (2012065).