Abstract
The effect of diisocyanate chain extender (CE) on the mechanical, rheological, and relaxation properties, as well as on molecular weight and crystallizability, of starting poly(ethylene terephthalate) (PET) and its composites containing carbon nanomaterials (CNM) such as carbon nanotubes (CNTs) and commercial carbon (CC) has been studied. The composites were compounded in molten PET using twin-screw extruder (screw diameter 35 mm; <svg style="vertical-align:-0.17555pt;width:60.325001px;" id="M1" height="10.9125" version="1.1" viewBox="0 0 60.325001 10.9125" width="60.325001" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,10.9125)"> <g transform="translate(72,-63.27)"> <text transform="matrix(1,0,0,-1,-71.95,63.5)"> <tspan style="font-size: 12.50px; " x="0" y="0">L</tspan> <tspan style="font-size: 12.50px; " x="7.6393328" y="0">/</tspan> <tspan style="font-size: 12.50px; " x="11.115167" y="0">D</tspan> <tspan style="font-size: 12.50px; " x="23.605663" y="0">=</tspan> <tspan style="font-size: 12.50px; " x="35.646053" y="0">4</tspan> <tspan style="font-size: 12.50px; " x="41.897552" y="0">0</tspan> </text> </g> </g> </svg>). To improve the distribution of CNM in the polymeric matrix (before introduction into the melt), they were blended with PET powder and subjected to an ultrasonic treatment in methylene chloride. The salient features of the materials structure were estimated based on DSC and relaxation spectrometry (dynamic mechanical analysis) data. It has been found that CNM additives partly suppress the PET-chain extension reactions which take place during interaction between macromolecular end groups and CE. Besides, both CNT and CC favour crystallizability of the modified PET owing to nucleation of the crystallization process. The influence of CNT appears to be more effective than that of CC. Enhancements in true mechanical strength and deformability of PET/CE/CNM composites, as against PET/CE materials, were found to be most clearly exhibited by the CNT-containing composites.
Highlights
The effect of diisocyanate chain extender (CE) on the mechanical, rheological, and relaxation properties, as well as on molecular weight and crystallizability, of starting poly(ethylene terephthalate) (PET) and its composites containing carbon nanomaterials (CNM) such as carbon nanotubes (CNTs) and commercial carbon (CC) has been studied
The addition of CE leads to the increase of intrinsic viscosity and noticeable reduction of melt flow index (MFI) values, which results from increased molecular weight of PET [4, 15]
Mn’s growth (MFI reduction) of PET containing CNM is not very substantial. This can be explained by high adsorptive surface activity of CNT and CC that causes partly blocking CE s isocyanate groups, and the decrease of the output of products of its interaction with ending groups of PET macromolecules [12, 14]
Summary
The effect of diisocyanate chain extender (CE) on the mechanical, rheological, and relaxation properties, as well as on molecular weight and crystallizability, of starting poly(ethylene terephthalate) (PET) and its composites containing carbon nanomaterials (CNM) such as carbon nanotubes (CNTs) and commercial carbon (CC) has been studied. The calculated true strength values of the material (Table 2) show maximum tensile strength σtt for Composition IV, containing CE and CNT—0.05 wt.% exceeds 300 MPa. It appears that PET containing CE and CNT tends to have orientational stretching and its strength considerably increases.
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