Different tougheners including methyl methacrylate-butadiene-styrene terpolymer (MBS, core-shell type), maleic anhydride (MAH) grafted ethylene-octene copolymer (EOM), and MAH grafted polyethylene wax (PEM) were investigated for toughening the polycarbonate (PC) composites reinforced by short carbon fiber (SCF) and flake graphene (FG). The effects of tougheners on the preparation, thermal conductivity and mechanical properties of PC composites were studied. Scanning electron microscopy was used for characterizing the impact fracture surfaces of the composites. The results showed that introducing tougheners into the carbon reinforced PC composites was beneficial to improving the processability, and PEM was more effective than EOM and MBS. Meanwhile, the through-thickness and the in-plan thermal conductivity decreased to some degree due to the isolated island effects of tougheners. Moreover, the brittle PC composites with high flexural stress could be easily toughened by tougheners. In contrast, PEM had better toughening function than EOM and MBS, and correspondingly, the stiffness of the composites was the lowest for the PEM toughened systems. The fractography revealed that dense and uniformly distributed carbon fillers dispersed in matrix PC and circular cavities coexisted in the composites. The naked fiber length gradually increased as the ductility of composite materials improved.
Carbon materials, such as carbon fiber, carbon nanotube, graphene, etc., have been commonly studied for enhancing the mechanical, electrical and thermal properties of thermoplastic or thermosetting resins. These modified composites generally exhibit low thermal expansion, light-weighting, good heat dissipation, high stiffness, and can be potentially applied in integrated circuits, satellite devices, electrnonics packaging and encapsulation, and thermal management fields where higher thermal conductivity required [
Generally speaking, factors determining the thermal and mechanical properties of composites include the surface treatment and interfacial structure, alignment and packing structure, aspect ratio, volume fraction, size, shape, purity, polydispersity and intrinsic conductivity of fillers, etc. [
At the same time, heterogeneous or hybrid fillers have been demonstrated as another effective method for enhancing the thermal and mechanical properties of polymer composites [
Polycarbonate-based thermoplastic composites have been prepared and studied using different carbon materials as modifying fillers [
First, confirm that you have the correct template for your paper size. This template has been tailored for output on the custom paper size (21 cm * 28.5 cm). A fixed quantity of silane coupling agent (SCA) was dispersed in the white oil (WO), and the obtained solution was poured into the FGs and SCFs. Stir the mixture until fully mixed. The modified fillers were proportionally mixed with the dried PC pellets and/or toughening agent (TA) for 3 minutes by a high speed mixer. The compound was melt blended in a twin-screw extruder (Leistritz, German) to prepare PC composites. The compositions of the PC composites prepared are listed in
Formula | Content (weight, %) | |||||
---|---|---|---|---|---|---|
PC | TA | SCF | FG | SCA | WO | |
Control | 70 | 0 | 25 | 5 | 0.3 | 1.6 |
+MBS | 65 | 5 | 25 | 5 | 0.3 | 1.6 |
+EOM | 65 | 5 | 25 | 5 | 0.3 | 1.6 |
+PEM | 65 | 5 | 25 | 5 | 0.3 | 1.6 |
Differential scanning calorimetry (DSC): The melting behaviors of the PC composites using different tougheners were determined using a differential scanning calorimeter (TA Instruments, USA). Experiments were performed with about 5 mg samples under dry nitrogen gas condition. First, the sample was heated to 200˚C - 250˚C at a rate of 10˚C/min and then held at 200˚C - 250˚C for 1 min. Subsequently, the sample was cooled at a rate of 10˚C/min to −50˚C and held at −50˚C for 1 min. It was then scanned from −50˚C to 250˚C - 300˚C at a heating rate of 10˚C/min. The melting temperature or glass transition temperature was obtained from the second-heating thermogram.
Thermal conductivity: In-plane and through-thickness thermal conductivity data of the composites were measured at 25˚C by using a LFA467 laser flash analyzer (NETZSCH, Germany) according to ASTM E1461 standard. Square test samples with a dimension of 6 mm × 6 mm × 1 mm and a dimension of 10 mm × 10 mm × 1 mm were used for testing, respectively.
Mechanical properties: Notched Izod impact strength was determined with a RESIL6957 impact tester (CEAST, Italy) according to ISO 179-1: 2010. The size of specimens was 80 mm × 10 mm × 4 mm and the depth of notch was 2 mm. Flexural strength and modulus were measured on a 3344 universal material testing machine (Instron, USA) at a bending rate of 2 mm/min and a span of 64 mm according to ISO 178-2010. The specimens had a size of 80 mm × 10 mm × 4 mm. Not less than 5 specimens were used for each mechanical testing.
Morphology: Prior to scanning electron microscopy (SEM) observations, all fracture surfaces of the impact specimens were sputter-coated with gold. Fractographic studies with SEM were conducted on the fracture surfaces by a Merlin field-emission scanning electron microscope (FE-SEM) (Carl Zeiss, Germany).
PC composites reinforced by short carbon fiber and flake graphene and three kinds of tougheners were prepared by using a twin screw extruder to achieve high intensity mixing and good dispersion of the modifiers. The objective of this research was to enhance the toughness of the PC composites. Following the composite preparation, the thermal properties of the materials were characterized, the resulting DSC curves of untoughened and toughened composites are shown in
The melt temperature of PC composite and the torque of twin-screw extruder during the extrusion were recorded and summarized in
the PE wax as toughening agent. In fact, PE wax is typically applied as a compatilizer or surface modifier in the composite materials. In this work, we found that PE was can effectively improve the processability of carbon materials filled PC composites. The lower parameter values of PE was system relative to EO copolymer system was mainly due to the difference in the melting points of PE wax and EO copolymer. The lower the melting temperature of toughener, the lower the parameter values, and the easier the composite preparation process. Moreover, a slightly reduced parameter values of MBS system as compared to the control case are probably due to the poor heat resistance properties of MBS.
For a polymer composite material to possess good thermal conductive properties, it needs an effective thermal conductive paths and network in its interior structures. The through-thickness and in-plane thermal conductivity data of the PC composites are shown in
As shown in
In order to explain the structure-property relationship observed above,
Core-shell type and grafting type tougheners were applied for enhancing the
toughness of SCF and FG reinforced PC composites. These tougheners were found to be effective in reducing the melt temperatures and torque during the extrusion process of the composites, and helped to improve the preparation process of composites. Unfortunately, tougheners are incompatible with PC matrix and formed isolated islands in matrix. The thermal conductivity of the toughened composites, either in parallel or perpendicular to extrusion direction, was found to decrease in the presence of a toughener. At the same time, the toughening effect of PEM was better than that of EOM, and MBS has lowest toughening effectiveness. The trend of flexural stress was opposite as the toughening effectiveness. The ductile composites displayed fiber breaking and peeling from PC matrix and cavitation, accompanied with the gradually increased length of naked fibers in the toughen composites.
The authors thank Dr. Yu Wang for the morphology characterization and the reviewers for the helpful discussions and suggestions.
Yu, Z.X., Bai, Y., Li, Y.C., Wang, W. and Wang, J.H. (2018) Preparation and Performance of Short Carbon Fiber and Flake Graphene Reinforced Polycarbonate Composites: Effects of Different Tougheners. Journal of Materials Science and Chemical Engineering, 6, 81-89. https://doi.org/10.4236/msce.2018.67009