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Shear and thermal processing can greatly influence nanoparticles' orientation and dispersion, affecting the nanocomposites' conductivity and mechanical properties. The synergistic effects of shear flow and Carbon nanotubes (CNTs) nucleating ability on the crystallization mechanisms have been proven. In this study, Polylactic acid/Carbon nanotubes (PLA/CNTs) nanocomposites were produced by three different molding methods: compression molding (CM), conventional injection molding (IM), and interval injection molding (IntM). Solid annealing at 80 °C for 4 h and pre-melt annealing at 120 °C for 3 h was applied to research the CNTs' nucleation effect and the crystallized volume exclusion effect on the electrical conductivity and mechanical properties. The volume exclusion effect only significantly impacts the oriented CNTs, causing the conductivity along the transverse direction to rise by about seven orders of magnitude. In addition, the tensile modulus of the nanocomposites decreases with the increased crystallinity, while the tensile strength and modulus decrease. [ABSTRACT FROM AUTHOR]

The orientation and dispersion of nanoparticles can greatly influence the conductivity and mechanical properties of nanocomposites. In this study, the Polypropylene/ Carbon Nanotubes (PP/CNTs) nanocomposites were produced using three different molding methods, i.e., compression molding (CM), conventional injection molding (IM), and interval injection molding (IntM). Various CNTs content and shear conditions give CNTs different dispersion and orientation states. Then, three electrical percolation thresholds (4 wt.% CM, 6 wt.% IM, and 9 wt.% IntM) were obtained by various CNTs dispersion and orientations. Agglomerate dispersion (Adis), agglomerate orientation (Aori), and molecular orientation (Mori) are used to quantify the CNTs dispersion and orientation degree. IntM uses high shear to break the agglomerates and promote the Aori, Mori, and Adis. Large Aori and Mori can create a path along the flow direction, which lead to an electrical anisotropy of nearly six orders of magnitude in the flow and transverse direction. On the other hand, when CM and IM samples already build the conductive network, IntM can triple the Adis and destroy the network. Moreover, mechanical properties are also been discussed, such as the increase in tensile strength with Aori and Mori but showing independence with Adis. This paper proves that the high dispersion of CNTs agglomerate goes against forming a conductivity network. At the same time, the increased orientation of CNTs causes the electric current to flow only in the orientation direction. It helps to prepare PP/CNTs nanocomposites on demand by understanding the influence of CNTs dispersion and orientation on mechanical and electrical properties. [ABSTRACT FROM AUTHOR]

Due to the properties of a positive temperature coefficient (PTC) effect and a negative temperature coefficient (NTC) effect, electrically conductive polymer composites (CPCs) have been widely used in polymer thermistors. A dual percolated conductive microstructure was prepared by introducing the polybutylene adipate terephthalate phase (PBAT) into graphene nanoplatelets (GNPs)-filled polylactic acid (PLA) composites, intending to develop a favorable and stable PTC material. To achieve this strategy, GNPs were selectively distributed in the PBAT phase by injection molding. In this study, we investigated the crystallization behavior, electrical conductivity, and temperature response of GNP-filled PLA/PBAT composites. The introduction of GNPs into PLA significantly increased PLA crystallization capacity, where the crystallization onset temperature (To) is raised from 116.7 °C to 134.7 °C, and the crystallization half-time (t1/2) decreases from 35.8 min to 27.3 min. The addition of 5 wt% PBAT increases the electrical conductivity of PLA/PBAT/GNPs composites by almost two orders of magnitude when compared to PLA/GNPs counterparts. The temperature of the heat treatment is also found to play a role in affecting the electrical conductivity of PLA-based composites. Increasing crystallinity is favorable for increasing electrical conductivity. PLA/PBAT/GNPs composites also show a significant positive temperature coefficient, which is reflected in the temperature–electrical resistance cycling tests. [ABSTRACT FROM AUTHOR]

In this work, a facile strategy is proposed to prepare highly electrically conductive polypropylene (PP)/polyolefin elastomer (POE)/multiwalled carbon nanotubes (MWCNTs) composites with ordered conductive networks using a house‐made die‐drawing apparatus. Results showed that increasing either die‐drawing speed or drawing ratio led to an increase of crystallinity by 10% and orientation factor by 0.15 for PP, respectively, which played an important role in tuning the electrical conductivity and mechanical properties. Prior to die‐drawing process, MWCNTs were selectively distributed in POE domains, resulting in a remarkable increase of electrical conductivity. The prevailing high‐stress field during die‐drawing process was able to deform MWCNTs‐enriched POE domains to ordered microfibrillar structure, as confirmed by morphology observations. This resulted in a further increase of electrical conductivity for die‐drawn PP/POE/MWCNTs composites when compared with that of MWCNTs‐containing counterparts without die‐drawing. Moreover, both the tensile strength and elongation at break for die‐drawn PPCNTE30 composites were increased by 20% and 127% as compared with their counterparts without die‐drawing treatment. [ABSTRACT FROM AUTHOR]

To obtain a super‐toughness and low seepage threshold for the conductivity of biodegradable soft polymer material, biodegradable polybutylene succinate (PBS)‐based composites with different contents of polyvinyl butyral (PVB) and multi‐wall carbon nanotubes (MWCNTs) were prepared by melt‐blending method. Synergy effects of different modified MWCNTs and PVB on the morphology, crystallization, and electrical and mechanical properties of MWCNTs/PVB/PBS composites were examined by Fourier Transform Infrared Spectroscopy (FTIR), scanning electron microscope (SEM), transmission electron microscopy (TEM), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), polarizing microscope (POM), resistance tester, and universal testing machine. Compared with pure PBS, with increasing MWCNT content, the electrical conductivity of the MWCNTs/PBS composites showed an upward trend, and the percolation threshold for electrical conductivity of the MWCNTs/PBS composites reached 0.47%. The electrical conductivity of the PBS composite mixed with 1.0 wt% of surface modified MWCNTs slightly increased by one order of magnitude compared with that of pure PBS. By adding 20 wt% of the PVB and 1 wt% of the unmodified MWCNTs, the electrical conductivity of the MWCNTs/PVB/PBS composite increased by seven orders of magnitude compared with that of pure PBS. The percolation threshold for electrical conductivity of the MWCNTs/PVB/PBS composites decreased to 0.049% owing to the formation of double percolation structure. Furthermore, compared with pure PBS, when the PVB content was 20 wt%, and the MWCNTs was 1 wt%, the elongation at break and V‐notch impact strength of PBS‐based composite dramatically increased by approximately 300% and 12‐fold, respectively. [ABSTRACT FROM AUTHOR]

In this study, the associations between the structural evolution and physical properties of polypropylene/poly(ethylene‐co‐octene)/multiwalled carbon nanotube (PP/POE/MWCNTs) composites were established. The MWCNTs particles preferentially migrating from PP matrix to disperse in POE phase, which contributed to a richer network structure, thus resulting in a significant improvement for electrical conductivity, as well thermal stability, and toughness property with the elongation at break from 300% to 800%. Furthermore, the online strain‐resistance analysis showed that introducing POE phase had a big advantage in improving the recovering resilience and stability of the conductive network structure of PP/POE/MWCNTs composites under a multi‐time circular tensile test with a strain of 5%. It was highlighted that the maximum and minimum electrical conductivity levels of PP/POE composites remained almost constant and even the ratio of the real‐time resistance to the initial one was negative just at the beginning of each circulation regarding the strain stretching and recovery. This was attributed to the oriented conductive network structure of PP/POE nanocomposites induced by the applied strain, thereby increasing the electrical conductivity. Overall, this research provides a basic guidance for preparing composites with ultrahigh flexibility and stability under a circular deformation, which is an essential element taken into consideration for smart sensors with high sensitivity. [ABSTRACT FROM AUTHOR]

Morphological evolution under shear, during different injection processes, is an important issue in the phase morphology control, electrical conductivity, and physical properties of immiscible polymer blends. In the current work, conductive nanocomposites were produced through three different injection-molding methods, namely, conventional injection molding, multi-flow vibration injection molding (MFVIM), and pressure vibration injection molding (PVIM). Carbon nanotubes in the polyamide (PA) phase and the morphology of the PA phase were controlled by various injection methods. For MFVIM, multi-flows provided consistently stable shear forces, and mechanical properties were considerably improved after the application of high shear stress. Shear forces improved electrical property along the flow direction by forming an oriented conductive path. However, shear does not always promote the formation of conductive paths. Oscillatory shear stress from a vibration system of PVIM can tear a conductive path, thereby reducing electrical conductivity by six orders of magnitude. Although unstable high shear forces can greatly improve mechanical properties compared with the conventional injection molding (CIM) sample, oscillatory shear stress increases the dispersion of the PA phase. These interesting results provide insights into the production of nanocomposites with high mechanical properties and suitable electrical conductivity by efficient injection molding. [ABSTRACT FROM AUTHOR]

Melt mixed polypropylene/polyamide 6 (PA6) and multiwalled carbon nanotubes (CNTs) were molded by compression, injection, and interval injection molding. PA phase exists as an isolated dispersed phase in the sea–island system with different phase orientations and dispersion degrees. CNTs prefer to be located in the minor PA phase because of their remarkable compatibility. However, when the content of CNTs is high enough, a conductive path can be formed regardless of the phase morphology. Moreover, when the CNT content is low, the dispersed PA forms an unelongated structure, which is beneficial to electrical conductivity. Although the elongated PA phase holds advantages in terms of its tensile properties, its conductivity network is defective. These results were proposed to uncover the influence of dispersed phase morphology on mechanical and electrical conductivity. [ABSTRACT FROM AUTHOR]