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Using polypropylene (PP) as a matrix and carbon nanotube (CNTs) as a modified material to prepare CNTs/PP composites, the effects of solid-phase drawing and CNTs on properties of PP-based composites after solid-phase drawing were analyzed. Crystallization, mechanical and electromagnetic shielding properties of the composites were studied by wide angle X-ray diffraction, 2D wide angle X-ray diffraction, small angle X-ray scattering, differential scanning calorimetry, polarizing microscope, scanning electron microscope, universal test machine, and vector analyzer. The results show that the solid-phase drawing and CNTs increase the tensile strength of the composite and reduce its elongation at break; the addition of CNTs plays a clear heterogeneous nucleation, refines the grain and improve the crystallinity, and the crystal formation of the CNTs/PP composite before and after the solid-phase drawing does not change, but the α-crystal for PP is improved significantly. The crystallinity of the composites is slightly decreased with increasing solid-phase drawing rate. The solid-phase drawing treatment and CNTs can improve the electromagnetic shielding performance, but make the electromagnetic shielding performances reduce after high drawing rate treatment.

Multiflow injection molding is used to prepare a highly oriented shish-kebab structure, and the mechanical properties of Polypropylene in the weak direction (WD) and strong direction (SD) are analyzed in this work. The oriented structure shows strong anisotropy. For example, the impact strength in SD is 6 times that of WD. One or three minutes of high-temperature-annealing (HTA, 30[degrees]C higher than [T.sub.m]) has been proven to be an effective method to trigger the partial melting and re-crystallization process, which in turn, can improve the shish-kebab structure and greatly improve yield and impact strength in both WD and SD. Furthermore, results confirm that the chains in the amorphous region play a key role in the mechanical properties in the WD, while the shish-kebab crystal structure determines the properties in the SD. Using shish-kebab structure and HTA to improve mechanical properties in both SD and WD directions will be helpful to avoid generating fiber composites that create recycling difficulties and loss of properties with cycle times. KEYWORDS annealing, crystallization, mechanical properties, polypropylene, shish-kebab structure, 1 | INTRODUCTION Many studies have been conducted on improving the mechanical properties of injection molded parts by adding fillers. However, this method either hampers efficient plastic recycling and increases [...]

The influence of different shear stresses induced by changing injection molding speeds on molecular chain orientation and lamellar branching of [beta]-nucleated iPP/poly(ethylene terephthalate) (PET) microparts was investigated using two-dimensional wide-angle X-ray diffraction and 2D-small-angle X-ray scattering. Results indicated that the prevailing shear stress can promote the formation of parent-daughter [alpha]-crystal structure and twisted shish-kebab structure in subsequent microparts. The diffraction of (300) plane of [beta]-crystals was also observed at varying injection speeds. Increasing injection speeds can significantly enhance the content of [beta]-crystals from 24 to 41% for [beta]-nucleated iPP microparts. Additionally, the content of [beta]-crystals was further enhanced in P-nucleated iPP/PET microparts with in situ formation of PET microfibrils under intensive shearing conditions. The addition of both PET and P-nucleation agents coupling with high shearing conditions exerts a synergetic effect on the development of [beta]-crystals. However, the orientation degree of crystal lattice decreased with increasing injection speeds for both [beta]-nucleated iPP and iPP/PET microparts. KEYWORDS crystallization, microinjection molding, microstructure, polypropylene, 1 | INTRODUCTION Recently, the development of miniature devices has attracted attention as more and more functions are being integrated into small systems. [1-3] Also, microinjection molding (MIM) has become [...]

In this work, the synergistic effect of using multiwalled carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) to regulate the temperature response of electrical conductivity (σ) for poly(lactic acid) (PLA) composites were reported. The addition of CNTs into PLA/GNPs composites markedly enhanced their crystallization capacity and σ, resulting in a reduction of percolation threshold from 2.87 (for PLA/GNPs) to 0.39 wt% (for PLA/GNPs/CNTs), which is attributed to the formation of a three‐dimensional conductive network within PLA consisting of CNTs and GNPs. Furthermore, elevating the heat treatment temperature from 80 to 140°C resulted in a reduced response time of PLA/CNTs/GNPs composites from 57 to 43 s at the Tend of 140°C. Notably, the combined use of CNTs and GNPs considerably amplified the value and stability of max ∆R/R0. For example, the maximum ∆R/R0 increased from 120% for PLACNT0.6 to 240% for PLA/(CNT1/GNP1)0.6. The suppression of volume expansion of PLA led to a negative temperature coefficient (NTC) effect at relatively low temperatures, resulting in a reduction of NTC transition temperature from about 160 to 110°C. Additionally, the PLA/(CNT1/GNP1)0.6 exhibited a swift and sensitive response to temperature fluctuations in various heating scenarios, which demonstrated a potential for use as a thermosensitive material with fast response and temperature‐sensing ability. Highlights: PLA‐based composites with NTC effect was prepared by adding CNTs and GNPs.The transition temperature from PTC to NTC effect decreased by adding hybrid fillers.The addition of hybrid CNTs and GNPs favored the formation of conductive network.The mechanism for NTC transition was explained. [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 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]

The influence of different shear stresses induced by changing injection molding speeds on molecular chain orientation and lamellar branching of β‐nucleated iPP/poly(ethylene terephthalate) (PET) microparts was investigated using two‐dimensional wide‐angle X‐ray diffraction and 2D‐small‐angle X‐ray scattering. Results indicated that the prevailing shear stress can promote the formation of parent–daughter α‐crystal structure and twisted shish–kebab structure in subsequent microparts. The diffraction of (300) plane of β‐crystals was also observed at varying injection speeds. Increasing injection speeds can significantly enhance the content of β‐crystals from 24 to 41% for β‐nucleated iPP microparts. Additionally, the content of β‐crystals was further enhanced in β‐nucleated iPP/PET microparts with in situ formation of PET microfibrils under intensive shearing conditions. The addition of both PET and β‐nucleation agents coupling with high shearing conditions exerts a synergetic effect on the development of β‐crystals. However, the orientation degree of crystal lattice decreased with increasing injection speeds for both β‐nucleated iPP and iPP/PET microparts. [ABSTRACT FROM AUTHOR]