Low-dimensional carbonaceous nanofiller induced polymer crystallization

Low-dimensional carbonaceous nanofillers (LDCNs), i.e., fullerene, carbon nanofiber, carbon nanotube, and graphene, have emerged as a new class of functional nanomaterials world-wide due to their exceptional electrical, thermal, optical, and mechanical properties. One of the most promising applications of LDCNs is in polymer nanocomposites; these materials endow the polymer matrix with significant physical reinforcement and/or multi-functional capabilities. The relations between properties, structure and morphology of polymers in the nanocomposites offer an effective pathway to obtain novel and desired properties via structure manipulation, wherein the interfacial crystallization and the crystalline structure with the matrix are critical factors. By now, extensive studies have reported that LDCNs are highly effective nucleating agents that can significantly accelerate their crystallization kinetics and/or induce unique crystalline morphologies in nanocomposites. This review presents a thorough survey of the current literature on the issues relevant to LDCN-induced polymer crystallization. After a brief introduction to each type of LDCN and its derivatives, LDCN-induced crystallization kinetics with or without flow fields, crystalline modification, and interfacial crystalline morphologies are thoroughly reviewed. Then, the origins of LDCN-induced polymer crystallization are discussed in depth based on molecular simulation and experimental studies. Finally, an overview of the challenges in probing LDCN-induced polymer crystallization and the outlook for future developments in polymer/LDCN nanocomposites conclude this paper. Understanding LDCN-induced polymer crystallization offers a helpful guidance to purposefully regulate the structure and morphology, then achieving high-performance polymer/LDCN nanocomposites.     

Enhanced interfacial adhesion via interfacial crystallization between sisal fiber and isotactic polypropylene: direct evidence from single‐fiber fragmentation testing

Bioresource natural sisal fiber (SF) was used to prepare single fiber‐reinforced isotactic polypropylene (iPP) composites. Three kinds of interfacial crystalline morphologies, spherulites, medium nuclei density transcrystallinity (MD‐TC) and high nuclei density transcrystallinity (HD‐TC), were obtained in the single fiber‐reinforced composites by implementing quiescent or dynamic shear‐enhanced crystallization and by modulating the compatibility interaction between SF and iPP. The development of interfacial shear strength (IFSS) during the interfacial crystallization process was demonstrated for the first time using a combination of single‐fiber fragmentation testing and optical microscope observation. A close correlation between IFSS and morphological characteristics of interfacial crystallization was well elucidated. The increases in IFSS were very different for spherulitic, MD‐TC and HD‐TC morphologies. The highest IFSS obtained was 28 MPa, after the formation of HD‐TC, which was about 62% of the tensile strength of neat iPP (45 MPa). These results offer powerful and direct evidence that interfacial crystallization could play an important role in the enhancement of interfacial adhesion of real SF/iPP composites. © 2013 Society of Chemical Industry     

Use of titanate to improve interfacial interaction and mechanical properties of polyethylene/artificial marble wastes composites

The resource utilization of artificial marble wastes (AMWs) is urgently needed for environmental protection as a large amount of artificial marble are used as construction material. Nevertheless, it still remains challenging to achieve high performance of AMWs-filled polymer composites due to their poor interfacial interaction with hydrophobic polyolefins. Here, the unsaturated resin residue on the surface of AMWs is employed to construct strong interfacial interaction with high-density polyethylene (HDPE) matrix to prepare mechanically robust polymeric composites by use of titanate coupling agent. The mechanical properties (with a tensile strength of 28.6 MPa and a flexural strength of 27.7 MPa) of the resulting composites are comparable to or even better than those of raw calcium carbonate-filled HDPE composites. This work will not only promote the recycling and reutilization of AMWs, but also provide a feasible way for value-added application of other polymeric wastes, such as waste printed circuit board, waste artificial turf, and so on.     

Effects of interfacial adhesion on properties of polypropylene/Wollastonite composites

Wollastonite reinforced polypropylene (PP/CaSiO₃) composites were prepared by melt extrusion. A silane coupling agent and a maleic anhydride grafted PP (PP‐g‐MA) were used to increase the interfacial adhesion between the filler and the matrix. The increased adhesion observed by scanning electron microscopy (SEM) resulted in improved mechanical properties. A model was applied to describe the relationship between the interfacial adhesion and tensile properties of PP/CaSiO₃ composites. There is stronger interfacial adhesion between silane‐treated CaSiO₃ and polymer matrix containing PP‐g‐MA as a modifier. Results of dynamic mechanical thermal analysis (DMTA) showed that stronger interfacial adhesion led to higher storage modulus. The influence of CaSiO₃ particles on the crystallization of PP was studied by using differential scanning calorimetry (DSC). The introduction of CaSiO₃ particles does not affect the crystallization temperature and crystallinity of PP matrix significantly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Interfacial interaction in AI(OH)3/polypropylene composites modified by insitu‐functionalized polypropylene

To investigate the interfacial interaction of AI(OH)₃/polypropylene (PP) composites modified by in situ‐functionalized polypropylene (FPP), AI(OH)₃/polypropylene (PP) composites containing a low AI(OH)₃ content, modified by in situ‐grafted acrylic acid, were prepared by a one‐step melt‐extrusion process. The effect of in situ FPP on the crystallization and melting behavior, crystalline morphology of the composites, and interfacial interaction between the filler and PP was investigated. The crystallization and melting behavior and crystalline morphology of PP in the composites depended upon the interfacial physical [heterogeneous nucleation of AI(OH)₃; cocrystallization and compabilitization of PP with in situ FPP] and the interfacial chemical interaction between both the components in the composites. FTIR results indicated that there exists a chemical reaction between AI(OH)₃ and in situ FPP. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 110–120, 2002; DOI 10.1002/app.10270     

Interfacial enhancement by shish-calabash crystal structure in polypropylene/inorganic whisker composites

The polymer matrix structure and the interface are strongly influenced by filler in semi-crystalline polymer composites because the fillers have the potential to nucleate the polymer crystallization. The structure of the nucleated crystalline polymer on filler is of particular interest and is a key to the interfacial enhancement. In this work, whiskers, with a large length/diameter ratio and with a diameter (0.2-2 μm) much larger than that of carbon nanotubes but much smaller than that of common fibers, were used to nucleate crystal morphology in polypropylene (PP)/whisker composites. The crystal morphology, interfacial adhesion and tensile properties of the composites were carefully investigated. A kind of peculiar shish-calabash crystallization morphology, with whisker serves as shish and PP spherulites serves as calabash, was observed for the first time in the thin film via PLM and in the injection molded bars by SEM. The formation mechanism of this shish-calabash structure was attributed to be that only a few nuclei could be induced on the whisker surface, which develop into large PP spherulites without hindrance, and finally stringed by the whisker, forming the shish-calabash structure. As a result, a significant improvement of interfacial interaction and tensile properties has been achieved.     

Largely enhanced crystallization of semi-crystalline polymer on the surface of glass fiber by using graphene oxide as a modifier

Interfacial crystallization of polymer on the surface of filler not only offers crystallography interest but also has a potential to improve the interfacial interaction, which is a key for the preparation of high-performance polymer/filler composites. In this work, a new method is proposed to improve the interfacial crystallization between semi-crystalline polymer and glass fiber (GF) by introducing graphene oxide (GO) to the surface of amorphous GF. The coating of GO on GF surface is realized via electrostatic self-assembling of the oppositely charged GO and amino coupling agent modified GF (GF-NH₂). After the thermal reduction of the coated GO (RGO), RGO coated GF (GF-RGO) is obtained. The interfacial crystallization of isotactic polypropylene (iPP) and poly(l-lactide) (PLLA) on the surface of raw GF, GF-NH₂, and GF-RGO are investigated using Polarized light microscope (PLM). It is found that raw GF and GF-NH₂ has almost no nucleation ability on the polymers crystallization. However, transcrystalline structure can be successfully induced at the polymers/GF-RGO interface, indicating a significantly improved nucleation ability of GF-RGO for polymer crystallization. This work could provide a new way to control interfacial crystallization, thus the interfacial adhesion of polymer/filler composites, and could also find a new application for GO as well.     

原位形成FPP偶联Al(OH)3/PP中的界面相互作用研究

制备低含量Al(OH)3填充PP复合材料[Al(OH)3/PP]，研究原位形成的官能团化聚丙烯（FPP）在Al(OH)3/PP中的结晶、熔融行为，结晶形态，以及与各组分间的相互作用。研究认为，在复合材料中存在Al(OH)3与FPP间的化学作用，FPP与PP的相容与共结晶作用，Al(OH)3表面异相诱导成核作用，FPP对Al(OH)3表面异相诱导成核作用的活化作用等，从而改善了Al(OH)3/PP的物理与力学性能。     

Comparison of the mechanical properties and interfacial interactions between talc,kaolin, and calcium carbonate filled polypropylene composites

Three types of mineral fillers—talc, calcium carbonate (CaCO₃), and kaolin (10–40 wt % filler loadings)—were compounded with polypropylene (PP) with a twin‐screw extruder. The composites were injection‐molded, and the effects of the filler loading on the mechanical, flow, and thermal properties for the three different types of filled composites were investigated. The aim was to compare their properties and to deduce prospective filler combinations that would yield hybrid PP composites in following studies. The results showed that in most cases, the strength and stiffness of the talc‐filled PP composites was significantly higher than those of the CaCO₃‐ and kaolin‐filled PP composites. However, CaCO₃, being a nonreactive filler, increased the toughness of PP. The kaolin‐filled PP composites also showed some improvement in terms of strength and stiffness, although the increases in these properties were not as significant as those of the talc‐filled PP composites. The effects of interfacial interactions between the fillers and PP on the mechanical properties were also evaluated with semiempirical equations. The nucleating ability of all three fillers was studied with differential scanning calorimetry, and the strongest nucleating agent of the three was talc, followed by CaCO₃ and kaolin. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3315–3326, 2004     

Improved interfacial properties of carbon fiber-reinforced epoxy composites with Fe2O3/graphene nanosheets using a magnetic field

The performance of carbon fiber-reinforced composites largely depends on the properties of the fiber-matrix interface. Here, to improve the interfacial strength properties of carbon fiber/epoxy composites, we doped different concentrations of Fe₂O₃/graphene nanosheets onto the interfacial region of the carbon fiber composites by nano-coating technology. With the aid of the magnetic field, the arrangement of nanosheets could be controlled in the interface. The nanosheets can be arranged on the carbon fiber surface parallel or perpendicularly with different concentrations. The tensile strength and interfacial shear strength of the modified fiber microcomposites had increased by 22.1 and 44.4% respectively with 1.0 mg/mL Fe₂O₃/graphene nanosheets. The results indicated that the Fe₂O₃/graphene nanosheets have an important influence on the carbon fibers and carbon fibers composites.     

Restricted chain segment mobility in poly(amide) 6/clay nanocomposites evidenced by quasi-isothermal crystallization

Modulated temperature differential scanning calorimetry is used to explore the interactions between a poly(amide) 6 matrix and various types of clay reinforcement. During quasi-isothermal crystallization of the polymer/clay nanocomposites, an excess contribution is observed in the recorded heat capacity signal, due to reversible melting and crystallization. It is proposed that the magnitude of this excess contribution can be used to qualify the polymer/clay interfacial interaction, as it is directly linked to the segmental mobility of the polymer chains in the interphase region, where both the crystalline and amorphous polymer fractions are affected. It is shown that the interfacial interaction strongly depends on the type of clay filler used. These interactions play a key role in the development of specific material properties for the different types of nanocomposites. A simple interphase model for the poly(amide) 6/clay nanocomposites is proposed.     

Improvement of interfacial interactions in CF/PEEK composites by an s-PSF/graphene oxide compound sizing agent

The interfacial interactions of carbon fiber (CF)-reinforced polymer composites is a key factor affecting the overall performance of the material. In this work, we prepared a sulfonated poly(ether sulfone)–graphene oxide mixed sizing agent to modify the interface of CF/PEEK composites and improve the interfacial properties between the PEEK matrix and CF. Results showed that the mechanical and interfacial properties of CF/PEEK composites are improved by the sizing agent. Specifically, the flexural strength, flexural modulus and interlaminar shear strength of the materials reached 847.29 MPa, 63.77 GPa, and 73.17 MPa, respectively. Scanning electron microscopy confirmed markedly improved adhesion between the resin matrix and fibers. This work provides a simple and effective method for the preparation of high-performance CF/PEEK composites, which can improve the performance of composites without degrading the mechanical property of pristine CF.     

Composites of Ultrahigh‐Molecular‐Weight Polyethylene with Graphene Sheets and/or MWCNTs with Segregated Network Structure: Preparation and Properties

UHMWPE/MWCNT and UHMWPE/GNS composites with a segregated network are prepared. TEM and SEM images indicate that the conducting fillers are distributed on the UHMWPE surface and form a segregated conducting network. The percolation threshold of UHMWPE/GNS composites is ≈0.25 wt% and that of UHMWPE/MWCNT composites is 0.20 wt%. The electrical conductivity of UHMWPE/GNS composites is almost four orders of magnitude lower than that of the UHMWPE/MWCNT composites. For equivalent concentrations of GNS and MWCNT, the composites with hybrid fillers exhibit a lower percolation threshold and a higher conductivity than that with GNS or MWCNT alone. Due to the high strength of the fillers and the segregated network structure, the mechanical properties of the composites first increase and then decrease with increasing filler content.

     

Morphology and mechanical and electrical properties of oriented PVA-VGCF and PVA-MWNT composites

The composites poly(vinyl alcohol) (PVA) and vapor growth carbon fiber (VGCFs) and multi wall carbon nanotubes (MWNTs) were prepared by gelation/crystallization from the mixture of dimethyl sulfoxide (DMSO) and water (H₂O). The composite films were elongated to 5-10-fold uniaxially. The mechanical properties of PVA composites were improved significantly by introduction of VGCFs and MWNTs and also by the orientation of fillers. Compared to VGCFs, MWNTs was more effective to improve the electric conductivity of the composites because of its network structure. The change in the electrical conductivity for the PVA/MWNT composites containing 5 wt% MWNT was independent of the draw ratio up to eight-fold indicating no disruption of the network formation. A certain high level of filler content was proved to be necessary for the promotion of both mechanical and electrical properties in oriented composite.     

矿物填料填充聚乙烯/麦秸杆复合材料性能比较

以麦秸杆纤维（WSF）和高密度聚乙烯（PE?HD）为原料,以白云石粉、硅灰石粉及滑石粉为填充料,通过熔融混炼及注射成型的方法制备了PE-HD/WSF/填料复合材料,并通过差示扫描量热仪、扫描电子显微镜和电子万能试验机等考察分析了填料种类及含量对复合材料结晶性能、微观形貌和力学性能等的影响。结果表明,在WSF的含量为40 %的配比下,复合材料的拉伸和弯曲强度随填料含量的增多呈现先增大后减小的趋势;当填料含量为5 %时,PE-HD/WSF复合材料的各项力学性能达到最佳,且硅灰石的增强效果优于白云石、滑石粉,结晶速率也最大;而用填料部分代替PE-HD则会使复合材料的耐水性减弱,同样在5 %的填料含量下得到吸水率的极小值,白云石增强的复合材料吸水率最低;拉伸试样断面形貌显示,细小填料颗粒不同程度地镶嵌在WSF与基体PE-HD之间,减少了WSF与PE-HD的间隙,改善了界面结合性。     

A review of vapor grown carbon nanofiber/polymer conductive composites

Vapor grown carbon nanofiber (VGCNF)/polymer conductive composites are elegant materials that exhibit superior electrical, electromagnetic interference (EMI) shielding effectiveness (SE) and thermal properties compared to conventional conductive polymer composites. This article reviews recent developments in VGCNF/polymer conductive composites. The article starts with a concise and general background about VGCNF production, applications, structure, dimension, and electrical, thermal and mechanical properties. Next composites of VGCNF/polymer are discussed. Composite electrical, EMI SE and thermal properties are elaborated in terms of nanofibers dispersion, distribution and aspect ratio. Special emphasis is paid to dispersion of nanofibers by melt mixing. Influence of other processing methods such as in-situ polymerization, spinning, and solution processing on final properties of VGCNF/polymer composite is also reviewed. We present properties of CNTs and CFs, which are competitive fillers to VGCNFs, and the most significant properties of their composites compared to those of VGCNF/polymer composites. At the conclusion of the article, we summarize the most significant achievements and address the future challenges and tasks in the area related to characterizing VGCNF aspect ratio and dispersion, determining the influence of processing methods and conditions on VGCNF/polymer composites and understanding the structure/property relationship in VGCNF/polymer composites.     

Maleic anhydride grafted polypropylene as a coupling agent for polypropylene composites filled with ink‐eliminated waste paper sludge flour

Ink‐eliminated sludge flour (IESF), a waste residue from the recycling treatment of waste paper, is a promising new kind of filler for thermoplastic polymers with a good price/performance ratio and advantages for environmental protection. In this study, high‐impact polypropylene (PP) and maleic anhydride grafted polypropylene (MAPP) were chosen as a polymer matrix and a coupling agent, respectively, for the preparation of IESF/PP composites, and the structures and properties of the obtained composites were also investigated. The experimental results revealed that IESF not only induced the crystallization orientation of PP along the b axis but also had a restraining effect on the formation of the β phase during the recrystallization of PP from the melt; the addition of MAPP further strengthened this effect to some extent. In addition, the proper addition of MAPP was helpful for improving the thermal stability of the IESF/PP composites. With the strengthening of the interfacial interaction between the IESF and PP matrix by MAPP, the resultant efficient stress transfer from the PP matrix to the IESF particles led to increased tensile and flexural strength. However, the original greater rigidity of MAPP, with respect to PP, reduced the toughness of the composites and caused some negative effects on the impact strength and the elongation at break. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2320–2325, 2004     

Crystallization behavior and mechanical properties of bio‐based green composites based on poly(L‐lactide) and kenaf fiber

Bio‐based polymer composite was successfully fabricated from plant‐derived kenaf fiber (KF) and renewable resource‐based biodegradable polyester, poly(L ‐lactide) (PLLA), by melt‐mixing technique. The effect of the KF weight contents (0, 10, 20, and 30 wt %) on crystallization behavior, composite morphology, mechanical, and dynamic mechanical properties of PLLA/KF composites were investigated. It was found that the incorporation of KF significantly improves the crystallization rate and tensile and storage modulus. The crystallization of PLLA can be completed during the cooling process from the melt at 5°C/min with the addition of 10 wt % KF. It was also observed that the nucleation density increases dramatically and the spherulite size drops greatly in the isothermal crystallization with the presence of KF. In addition, with the incorporation of 30 wt % KF, the half times of isothermal crystallization at 120°C and 140°C were reduced to 46.5% and 28.1% of the pure PLLA, respectively. Moreover, the tensile and storage modulus of the composite are improved by 30% and 28%, respectively, by the reinforcement with 30% KF. Scanning electron microscopy observation also showed that the crystallization rate and mechanical properties could be further improved by optimizing the interfacial interaction and compatibility between the KF and PLLA matrix. Overall, it was concluded that the KF could be the potential and promising filler for PLLA to produce biodegradable composite materials, owing to its good ability to improve the mechanical properties as well as to accelerate the crystallization of PLLA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Conductive polymer composites with segregated structures

Conductive polymer composites (CPCs) have generated significant academic and industrial interest for several decades. Unfortunately, ordinary CPCs with random conductive networks generally require high conductive filler loadings at the insulator/conductor transition, requiring complex processing and exhibiting inferior mechanical properties and low economic affordability. Segregated CPC (s-CPC) contains conductive fillers that are segregated in the perimeters of the polymeric granules instead of being randomly distributed throughout the bulk CPC material; these materials are overwhelmingly superior compared to normal CPCs. For example, the s-CPC materials have an ultralow percolation concentration (0.005–0.1 vol%), superior electrical conductivity (up to 10⁶ S/m), and reasonable electromagnetic interference (EMI) shielding effectiveness (above 20 dB) at low filler loadings. Therefore, considerable progress has been achieved with s-CPCs, including high-performance anti-static, EMI shielding and sensing materials. Currently, however, few systematic reviews summarizing these advances with s-CPCs are available. To understand and efficiently harness the abilities of s-CPCs, we attempted to review the major advances available in the literature. This review begins with a concise and general background on the morphology and fabrication methods of s-CPCs. Next, we investigate the ultralow percolation behaviors of and the elements exerting a relevant influence (e.g., conductive filler type, host polymers, dispersion methods, etc.) on s-CPCs. Moreover, we also briefly discussed the latest advances in the mechanical, sensing, thermoelectric and EMI shielding properties of the s-CPCs. Finally, an overview of the current challenges and tasks of s-CPC materials is provided to guide the future development of these promising materials.     

Mechanism of size effects of a filler on the wear behavior of ultrahigh molecular weight polyethylene

Although the size effects of a filler are closely related to the complex multi-level structures of their polymer composites; unfortunately, such relationships remain poorly understood. In this study, we investigated the effects of various sizes (40-600 nm) of silicon carbide (SiC) fillers on the wear behavior of ultrahigh molecular weight polyethylene (UHMWPE) in the presence of the silane coupling agent KH-560. All of these SiC fillers improved the wear resistance of UHMWPE significantly, with a medium size (150 nm) being optimal. To examine the reasons for this behavior, we analyzed the multi-level structures of the samples in terms of their matrix structures (crystalline; amorphous; interphase), matrix-filler interactions (physical adsorption; chemical crosslinking; hybrid network) and the external effects of SiC fillers (bearing loads; transferring frictional heat). The high rigidity and thermal conductivity of SiC fillers and, more importantly, the intrinsic characteristics of the matrix structures (larger crystal grains; higher interphase; stronger amorphous entangled networks) were the key parameters affecting the enhancement in the wear-resistance of the UHMWPE. Herein, we also provide interpretations of the corresponding physical effects. Our results should improve our understanding of the structure-property relationships and, thus, should guide the formula design of UHMWPE composites.