Structure and Properties of Epoxy Resin/Graphene Oxide Composites Prepared from Silicon Dioxide-Modified Graphene Oxide

In this study, graphene oxide (GO) was modified via electrostatic interactions and chemical grafting by silica (SiO2), and two SiO2@GO hybrids (GO-A and GO-B, respectively) with different structures were obtained and carefully characterized. Results confirmed the successful grafting of SiO2 onto the GO surface using both strategies. The distribution of SiO2 particles on the surface of GO-A was denser and more agglomerated, while it was more uniform on the surface of GO-B. Then, epoxy resin (EP)/GO composites were prepared. The curing mechanism of EP/GO composites was studied by differential scanning calorimetry and in situ infrared spectra spectroscopy. Results of tensile tests, hardness tests, dynamic mechanical analysis, and dielectric measurement revealed that EP/GO-B exhibited the highest tensile properties, with a tensile strength of 79 MPa, a 43% increase compared to raw EP. Furthermore, the addition of fillers improved the hardness of EP, and EP/GO-B showed the highest energy storage modulus of 1900 MPa. The inclusion of SiO2@GO hybrid fillers enhanced the dielectric constant, volume resistivity, and breakdown voltage of EP/GO composites. Among these, EP/GO-B displayed the lowest dielectric loss, relatively good insulation, and relatively high volume resistivity and breakdown voltage. A related mechanism was proposed.

The Influence of Melt Status and Beta-Nucleation Agent Distribution on the Crystallization of Isotactic Polypropylene

Although being investigated extensively in past decades, the factors affecting β-crystallization in β-nucleating agent/iPP composites have not been identified completely. In this study, β-crystallization in mesomorphic melt and free melt...

Exploring the Effects of MXene on Nonisothermal Crystallization and Melting Behavior of β-Nucleated Isotactic Polypropylene

In this study, one of the commonly used MXene (Ti3C2Tx) and β nucleated isotactic polypropylene (β-iPP)/MXene composites of different compositions were fabricated. The effects of MXene on non-isothermal crystallization and polymorphic behavior of β-iPP/MXene composites were comparatively studied. The non-isothermal crystallization kinetics indicates that for all samples, the lower cooling rates promote composites to crystallize at higher temperatures. When MXene and β-Nucleating agent (β-NA) are added separately, the crystallization temperature of composites shifts towards higher temperatures at all cooling rates. When MXene and β-NA are added simultaneously, the composite shows different cooling rate dependence, and the effects of improving crystallization temperatures is more obvious under rapid cooling. The activation energy of four samples iPP, iPP/MXene, iPP/β-NA, and iPP/MXene/β-NA were -167.5, -185.5, -233.8, and -218.1 kJ/mol respectively, which agree with the variation tendency of crystallization temperatures. The polymorphic behavior analysis obtained from Differential Scanning calorimetry (DSC) is affected by two factors: the ability to form β-crystals and the thermal stability of β-crystals. Because β-crystals tend to recrystallize to α-crystals below a critical temperature, to eliminate the effect of β-α recrystallization, the melting curves at end temperatures Tend = 50 °C and Tend = 100 °C are comparatively studied. The results show that more thermally unstable β-crystals would participate in β-α recrystallization with higher cooling rates. Moreover, thermal stability of β-crystals is improved by adding MXene. To further verify these findings, samples of three different thermal conditions were synthesized and analyzed by DSC, X-Ray Diffraction (XRD), and Polarized Light Optical Microscopy (PLOM), and the results were consistent with the above findings. New understandings of synthesizing β-iPP/MXene composites with adjustable morphologies and polymorphic behavior were proposed.

Effects of graphene oxide size on curing kinetics of epoxy resin

To study the effects of graphene oxide (GO) size on the curing kinetics of epoxy resin (EP), two kinds of GO were selected and characterized by Fourier transform infrared spectrometry (FT-IR), FT-Raman spectrometry (FTIR-Raman), thermo gravimetric analysis (TGA), dynamic light scattering (DLS), transmission electron microscopy (TEM), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). The results showed that the two kinds of GO had similar chemical structures but different sizes-the average particle size of GO-A was 190.1 nm and that of GO-B was 1510 nm, and GO-A has more oxidizing groups on its surface. The two kinds of GO were separately added to EP, and the curing kinetics of GO/EP composites and neat EP were investigated through differential scanning calorimetry (DSC). It can be seen that the addition of GO promoted the curing process of the EP system, and GO-A had a more significant catalytic effect. Furthermore, the curing activation energy (E a) was calculated by Kissinger model, and the change of E a in the whole curing reaction process was studied by Ozawa method to further understand the curing mechanism. It showed that the apparent E a of EP system increases with the increase of the conversion rate, and E a of EP-A is obviously lower in the early curing stage. However, as the curing reaction proceeds, E a of EP-B is a little lower than that of EP-A in the later curing stage. But EP-A has the lowest E a combined with the whole process from Kissinger method. To sum up, it can be concluded that the curing process of EP can be promoted by adding GO and the smaller size (190.1 nm) of GO had a greater effect and lower E a than the GO with particle size of 1510 nm. And the related mechanisms were discussed and analyzed.

Investigation on the Effects of MXene and β-Nucleating Agent on the Crystallization Behavior of Isotactic Polypropylene

The effects of MXene on the crystallization behavior of β-nucleated isotactic polypropylene (iPP) were comparatively studied. The commonly used MXene Ti3C2Tx was prepared by selective etching and its structure and morphology were studied in detail. Then MXene and a rare earth β-nucleating agent (NA) WBG-II were nucleated with iPP to prepare samples with different polymorphic compositions. The crystallization, melting behavior, and morphologies of neat iPP, iPP/MXene, iPP/WBG-II, and iPP/MXene/WBG-II were comparatively studied. The crystallization behavior analysis reveals that a competitive relationship exists between MXene and WBG-II when they were compounded as α and β nucleating agents. In the system, the β-nucleation efficiency (NE) of WBG-II is higher than α-NE of MXene. The β-phase has relatively low thermal stability and would transform to α-phase when cooled below a critical temperature.

Exploring Impacts of Hyper-Branched Polyester Surface Modification of Graphene Oxide on the Mechanical Performances of Acrylonitrile-Butadiene-Styrene

In this manuscript, the graphene oxide (GO) was modified by hyper-branched polyester (HBP). The effects of GO or modified GO (HBP-m-GO) on the mechanical performance and wearing properties were investigated. The results of X-ray photoelectron spectra (XPS), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM) revealed the successful grafting of HBP onto GO. The thermogravimetric analysis (TGA) indicated that the graft amount of HBP is calculated to be 9.6 wt%. The GO or HBP-m-GO was added into acrylonitrile-butadiene-styrene copolymer (ABS) to prepare the ABS/GO composites. The mechanical properties and wear performance of the composites were studied to comparatively study the impact of GO modification on the properties of the composites. The results revealed that the addition of GO has a significant effect on the mechanical properties of ABS, and when HBP-m-GO was added, the elastic modulus and tensile strength of ABS/HBP-m-GO increased evidently compared with ABS/GO. The tensile strength increased from 42.1 ± 0.6 MPa of pure ABS to 55.9 ± 0.9 MPa, up to 30%. Meanwhile, the elongation at break was significantly higher than ABS/GO to 20.1 ± 1.3%, slightly lower than that of pure ABS. For wear performance, the addition of raw GO decreased the friction coefficient, and when the HBP-m-GO was added, the friction coefficient of the ABS/HBP-m-GO dropped more evidently. Meanwhile, the weight loss during the wear test decreased evidently. The related mechanism was discussed.

Impacts of Modified Graphite Oxide on Crystallization, Thermal and Mechanical Properties of Polybutylene Terephthalate

In this study, the surface modification on graphene oxide (GO) was performed using octadecylamine (ODA). Furthermore, polybutylene terephthalate/GO (PBT/GO) composites were prepared to elucidate the role of GO surface modification on the mechanical performance, thermal stability and crystallization behavior. Results of Fourier transform infrared spectra (FT-IR), Raman spectrum, thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM) revealed that ODA was successfully grafted on GO. Differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), tensile test, Izod impact strength test and TGA were carried out on the PBT/GO composites. Results indicated that the addition of raw GO can enhance the crystallization temperature and degree of crystallinity and can slightly improve the thermal stability and tensile strength of the composites. However, the impact strength and elongation at break were seriously decreased owing to the poor compatibility between the GO and PBT matrix. Once the modified GO was added, the crystallization temperature and degree of crystallinity were greatly increased. The tensile strength increased greatly while the elongation at break and Izod impact strength were efficiently maintained; these were evidently higher than those of PBT/raw GO. Moreover, thermal stability was greatly enhanced. SEM (scanning electron microscope) observation results on the impact-fractured surface clearly confirmed the improved compatibility between the modified GO and PBT matrix. A related mechanism had been discussed.

Ligno-Cellulosic Fibre Sized with Nucleating Agents Promoting Transcrystallinity in Isotactic Polypropylene Composites

The mechanical performance of composites made from isotactic polypropylene reinforced with natural fibres depends on the interface between fibre and matrix, as well as matrix crystallinity. Sizing the fibre surface with nucleating agents to promote transcrystallinity is a potential route to improve the mechanical properties. The sizing of thermo-mechanical pulp and regenerated cellulose (Tencel™) fibres with α- and β-nucleating agents, to improve tensile strength and impact strength respectively, was assessed in this study. Polarised microscopy, electron microscopy and differential scanning calorimetry (DSC) showed that transcrystallinity was achieved and that the bulk crystallinity of the matrix was affected during processing (compounding and injection moulding). However, despite substantial changes in crystal structure in the final composite, the sizing method used did not lead to significant changes regarding the overall composite mechanical performance.

Influences of Hyperbranched Polyester Modification on the Crystallization Kinetics of Isotactic Polypropylene/Graphene Oxide Composites

In this study, the hyperbranched polyester grafted graphene oxide (GO-H202) was synthesized, and the isotactic polypropylene/graphene oxide (iPP/GO) composites were prepared. Results of X-ray photoelectron spectra (XPS), Fourier transform infrared (FT-IR), and transmission electron microscopy (TEM) revealed the successful synthesis of GO-H202, while thermogravimetric analysis (TGA) indicated that the weight ratio of grafting was about 35 wt %. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) were carried out to investigate the role of GO and GO-H202 on the crystallization kinetics of the composites. Results suggested that the addition of GO enhanced the nucleation rate and crystallizability of the composites, while GO-H202 exhibited a higher crystallization acceleration effect compared to neat GO; results of isothermal crystallization kinetics and self-nucleation isothermal crystallization kinetics showed that both the overall crystallization rate and crystal growth rate increase after the addition of GO and GO-H202, and the crystallization acceleration of GO-H202 became evidently stronger compared to GO. Moreover, the variation trends of Avrami exponent n with the isothermal crystallization temperature TcISO changed significantly after the addition of GO or GO-H202, which might imply that the addition of GO and GO-H202 lead to different crystallization dimensionalities during the isothermal crystallization of the composites. The related mechanism was also discussed.

Exploring the Effects of Stereo-Defect Distribution on Nonisothermal Crystallization and Melting Behavior of β-Nucleated Isotactic Polypropylene/Graphene Oxide Composites

In this work, using two isotactic polypropylene (iPP) resins with similar average isotacticity and molecular weight but different uniformities of stereo-defect distribution, the β-nucleated iPP/graphene oxide (β-iPP/GO) composites (NPP-A and NPP-B) were prepared to investigate the effect of stereo-defect distribution on the nonisothermal crystallization kinetics and polymorphic melting behavior of the composites by means of scanning electron microscopy, wide-angle X-ray diffraction, and differential scanning calorimetry. The results showed that more uniform stereo-defect distribution led to a slight increase of the crystallization rate and decrease of the crystallization activation energy E c. NPP-B with more uniform stereo-defect was more favorable for the formation of a large amount of β-phase. Moreover, the role of the cooling rate was also discussed and it was found that the higher the cooling rate, the higher the β-phase content and the smaller the crystalline sizes, meanwhile, the higher the amount of β-phase with relatively lower thermal stability that will take part in β-α recrystallization during the subsequent melting process. For β-iPP/GO composites, although the cooling rate greatly influences the polymorphic behavior and crystalline structures of the composites, the uniformity of stereo-defect distribution was found to be the first factor determining the formation of the β-phase.

Effects of Polypropylene Orientation on Mechanical and Heat Seal Properties of Polymer-Aluminum-Polymer Composite Films for Pouch Lithium-Ion Batteries

In this study, polyamide-aluminum foil-polypropylene (PA-Al-PP) composite films with different orientation status of the PP layer were prepared, and their morphology, tensile, peeling and heat seal behavior were studied. The comparative study of tensile and fracture behaviors of single-layer film of PA, Al and PP, as well as the composite films of PA-Al, PP-Al and PA-Al-PP revealed that in PA-Al-PP composite film, the PA layer with the highest tensile strength can share the tensile stress from the Al layer during stretching, while the PP layer with the lowest tensile strength can prevent further development of the small cracks on boundary of the Al layer during stretching. Moreover, the study of heat seal behavior suggested that both the orientation status and the heat seal conditions were important factors in determining the heat seal strength (HSS) and failure behavior of the sample. Four failure types were observed, and a clear correspondence between HSS and failure types was found. The results also elucidated that for the composite film, only in the cases where the tensile stress was efficiently released by each layer during HSS measurement could the composite film exhibit desired high HSS that was even higher than its tensile strength.

Toward Subtle Manipulation of Fine Dendritic β-Nucleating Agent in Polypropylene

Dendritic β-nucleating agent (β-NA) can readily manipulate the formation of dendritic β-crystal with a unique toughening effect on polypropylene (PP) to drastically enhance the ductility. However, by the current method, the geometric size is too large to fully perform the nucleating efficiency. In this study, by comparatively investigating the effect of molecular weight of PP and diffusion of β-NAs in a PP melt, we proposed a novel carrier strategy that selective enrichment of β-NAs in a PP carrier was followed by directed migration into polymer matrix. Accordingly, the growth of NAs was controlled by the release from the PP carrier, which decreased the available amount of β-NAs during the growth stage. In this case, the viscosity difference between PP carrier and matrix determined the interfacial movement of β-NAs. When the PP carrier and matrix had same molecular weight, the diffusion and release became favorable to facilitate the formation of the dense and fine dendritic aggregates. As a result, the relative content of β-crystals reached 92%, with a drastic increase of ∼82% in the optimal condition compared to the directed compounded PP/β-NAs sample. This study can open a new avenue to tailor the topologies of β-NAs and the ensuing β-crystals for high-performance PP products.

Modeling of polystyrenic nanoparticles driven β-trans-crystalline efficiency in isotactic polypropylene

Addition of four styrenic soft nano-particles induced relative β-polymorphism as much as 20, 27, 34 and 10% during 10 minutes annealing of iPP at 116 °C. The kinetic and thermodynamic aspects of the phenomenon rationalized by a bi-exponential function

Unusual hierarchical structures of micro-injection molded isotactic polypropylene in presence of an in situ microfibrillar network and a β-nucleating agent

The morphological development of iPP in presence of an in situ microfibrillar network and a β-nucleating agent under micro-injection molding.

New understanding of the hierarchical distribution of isotactic polypropylene blends formed by microinjection-molded poly(ethylene terephthalate) and β-nucleating agent

Hierarchical distribution of β-crystals in microinjection molded poly(ethylene terephthalate)/β-nucleating agent-nucleated isotactic polypropylene blends.

Influence of lamellar structure on the stress–strain behavior of β nucleated polypropylene under tensile loading at elevated temperatures

Schematic diagram of the deformation mechanism of β-iPP with different lamellae distributions when stretched at elevated temperatures.

Pore formation mechanism of β nucleated polypropylene stretched membranes

Schematic diagram of pore formation mechanism of β-PP during stretching at 25 °C and 90 °C.