Influence of Carbon Nanotubes on the Crystallization and Directional Tensile Behavior of High-Density Polyethylene Prepared by Dynamic-Packing Injection Molding

The influence of multi-walled carbon nanotubes (MWCNTs) on the crystallization and directional tensile properties of high-density polyethylene (HDPE) was studied for samples prepared by dynamic-packing injection molding (DPIM). Oscillatory shear was imposed on the gradually cooled melt during the packing solidification stage of DPIM. For the oriented composites containing 1.8 wt% MWCNTs, the tensile fracture behavior showed typical brittle features along the flow direction (FD) and perpendicular direction (PD), which were almost the same as those that occurred in oriented pure HDPE. The elongation at break along both directions decreased due to the incorporation of MWNCTs in the oriented composites compared with the oriented pure HDPE. However, the tensile strength of the oriented HDPE/MWCNT composites was greatly improved along the FD due to the presence of carbon nanotubes; meanwhile, it was not weakened along the PD. In scanning electron microscopy observations, it was found that there were some oriented hybrid shish-kebab structures in a nanometre scale in the oriented HDPE/MWCNT composites, but not in its isotropic composites. This suggests that MWCNTs were involved in the shear-induced crystallization of HDPE. Differential scanning calorimetry measurements confirmed that the crystallinity of oriented HDPE composites with 1.8 wt% MWCNTs was higher than those of isotropic HDPE and isotropic composites, but was not obviously higher than that of oriented pure HDPE. These findings demonstrate that MWCNTs indeed affected the formation of crystalline structures, but did not greatly influence the crystallinity of HDPE under shear flow. The transition of crystalline morphology might be the reason for change in tensile behavior for the oriented HDPE/MWCNT composites compared with the oriented pure HDPE.     

Correlation of Oscillation Cycles and Crystallization in HDPE Blends with Small Amounts of HMWPE Prepared by Dynamic-Packing Injection Molding

The effect of oscillation cycles on crystal morphology was investigated for high-density polyethylene (HDPE) in blends with 4 wt% high molecular weight polyethylene (HMWPE) (labeled B4) in samples prepared through dynamic-packing injection molding (DPIM). With the aid of differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), a weblike shish-kebab morphology that markedly increased stiffness and toughness was found at a specific oscillation cycle. The DSC and SEM results showed that crystal morphology was altered with changes in the oscillation cycle. The SEM and TEM results showed that a much better weblike shish-kebab structure, in which most of the lamellae connect different columns compared with conventional shish-kebabs, was formed in the B4 samples when the oscillation cycle was 10s. These results show that a proper oscillation cycle favors the improvement of crystal structures in HDPE blends induced by a small amount of HMWPE.     

Self-Reinforced High-Density Polyethylene Prepared by Low-Frequency,Vibration-Assisted Injection Molding. 1. Processing Conditions and Physical Properties

Using a low-frequency, vibration-assisted injection molding (VAIM) device, the effects of vibration variables (frequency and amplitude) on mechanical properties and thermal softening temperature of high-density polyethylene (HDPE) injection moldings were investigated. For VAIM-processed samples, the mechanical properties can be improved by changing vibration frequency and vibration pressure amplitude. Injected at a constant vibration pressure amplitude, a low range of frequency (below 0.7 Hz) was favorable for increasing yield strength; in the high range of frequency (0.7 Hz < f < 2.33 Hz) the yield strength remained at a plateau. Injected at a constant frequency (0.7 Hz) the yield strength increased sharply with decreased elongation when applying large vibration pressure amplitude. The maximal yield strength and Young's modulus were 60.6 MPa and 2.1 GPa for a VAIM sample compared with 39.8 MPa and 1.0 GPa for a conventional injection-molded (CIM) sample, respectively; there was also a 10°C increase in Vicat softening point temperature.     

Study on Properties and Structure of Near Melt Point Extruded High‐Density Polyethylene

The effect of extrusion temperature on the mechanical properties of high‐density polyethylene (HDPE) was examined using solid‐state extrusion (SSE) and melt‐state extrusion (MSE) techniques. Differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) investigations were employed to provide evidence for explaining the relationship between mechanical properties and morphology of extrusion moldings. Extruded from a convergence‐divergence die, compared with samples obtained by MSE, the yield strength of samples obtained by SSE was enhanced in both longitudinal and transverse directions with a ductile failure. The yield strength decreased sharply with increasing extrusion temperature. The maximum longitudinal yield strength of samples extruded at 112°C was 181 MPa with an 87% elongation at break; the corresponding values were 28 MPa and 800% for samples extruded at 140°C (MSE); in the transverse direction the yield strength was 27 MPa with a 101% elongation at break for samples extruded at 140°C, while the maximum yield strength was 51 MPa with a 45% of elongation at break for samples extruded at 116°C. Compared with sheets extruded at 140°C, DSC data shows a 5.3°C increase in melting point, a 9.5°C decrease in melt point width, and a 7.1% decrease in crystallinity for sheets extruded at 112°C. SEM indicates that spherulites predominate in MSE samples, while a preferred orientation of the lamellae along the extrusion direction were mainly produced by SSE.     

Banana fiber strands–reinforced polymer matrix composites

Banana fiber (BF)-reinforced low-density polyethylene (LDPE) unidirectional composites were fabricated by the compression molding process with 40 wt% fiber loading. The fibers were modified with methylacrylate (MA) mixed with methanol (MeOH) along with 2% benzyl peroxide under thermal curing method at different temperatures (50–90 °C) for different curing times (10–50 min) in order to have better compatibility with the matrix. The effect of fiber surface modification on the mechanical properties (tensile and impact properties) of the composites were evaluated. Monomer concentration, curing temperature, and curing time were optimized in terms of polymer loading and mechanical properties. The mechanical properties were found to be improved based on the improved interaction between the reinforcement and the matrix. Optimized BFs were again treated with 2–5 wt% starch solutions and composites made of 4% starch treated BF showed the highest mechanical properties than that of MA treated composites. Scanning electron microscopy (SEM) was performed to get an insight into the morphology of the composites. Water uptake and soil degradation test of the composites were also investigated.     

Biaxially Self-Reinforced High-Density Polyethylene Prepared by Vibration-Assisted Injection Molding. I. Processing Conditions and Physical Properties

A pulse pressure was imposed on the melt in the injection molding cavity during the injection and holding pressure stages, called vibration-assisted injection molding (VAIM) technology. With the VAIM technology, biaxially self-reinforced high-density polyethylene (HDPE) samples were prepared and the physical properties affected by the vibration processing conditions were studied. The tensile properties can be improved in both the machine direction (MD) and the transverse direction (TD) by changing the vibration frequency and vibration pressure amplitude, respectively. The elongation at break increased with increasing the vibration frequency for the VAIM sample processed at constant low vibration pressure amplitude; the yield strength increased with increasing the vibration pressure amplitude for the VAIM sample prepared at constant low vibration frequency. The softening point temperature for the VAIM sample increased by 8°C compared with a conventional injection-molded (CIM) sample.     

Designing of multiwalled carbon nanotubes reinforced low density polyethylene nanocomposites for suppression of electromagnetic radiation

High aspect ratio multi-walled carbon nanotubes (MWCNTs) reinforced low density polyethylene (LDPE) composites were prepared by solvent casting followed by compression molding technique. Electromagnetic interference (EMI) shielding effectiveness (SE) of these composites was investigated in the frequency range of 12.4?C18 GHz (Ku-band) for the first time. The experimental results indicate that the EMI-SE of these composites is sensitive to the MWCNT loading. The average value of EMI-SE reaches 22.4 dB for 10 wt% MWCNT-LDPE composites, indicating the usefulness of this material for EMI shielding in the Ku-band. The main reason for improved SE has been attributed to significant improvement in the electrical conductivity of the composites by 20 orders of magnitude, i.e., from 10^?20 for pure LDPE to 0.63 S/cm for MWCNT-LDPE, which is three order of magnitude higher than the previous reports for MWCNT-LDPE composites. Differential scanning calorimetry of the MWCNT-LDPE composites showed around 37% improvement in the crystalline contents over pure LDPE samples which resulted into enhanced thermal stability of the composites. The thermal decomposition temperature of LDPE is shifted by 40 °C on addition of 5 wt% MWCNT. The studies therefore show that these composite can be used as light weight, thermally stable EMI shielding, and antistatic material.     

Enhanced surface free energy of polyimide fibers by alkali treatment and its interfacial adhesion behavior to epoxy resins

In this article, polyimide (PI) fibers were modified by alkali treatment, and PI fiber-reinforced epoxy composites were fabricated. The effects of different alkali treatment times on the surface properties of the PI fibers and the adhesion behaviors of PI fiber/epoxy composites were studied. The surface morphologies, chemical compositions, mechanical properties, and surface free energy of the PI fibers were characterized by atomic force microscopy, X-ray photoelectron spectroscopy, single-fiber tensile strength analysis, and dynamic contact angle analysis, respectively. The results show that alkali treatment plays an important role in the improvement of the surface free energy and the wettability of PI fibers. We also found that, after the 3 min, 30 °C, 20 wt% NaOH solution treatment, the fibers possessed good mechanical properties and surface activities, and the interlaminar shear strength of the composites increased to 64.52 MPa, indicating good interfacial adhesion properties.     

Melt Vibration Improved Melt Flow Behavior and Mechanical Properties of High Density Polyethylene

A pulse pressure was superimposed on the melt flow resulting in melt vibration. With application of the melt vibration technology, the melt flow behavior and mechanical properties of high‐density polyethylene were studied. For vibration‐assisted extrusion (VAE) at constant vibration pressure amplitude, the viscosity decreases sharply with increasing vibration frequency, and also does so when increasing vibration pressure amplitude for VAE at constant vibration frequency. The effect of vibration field on melt rheological behavior is also related to the melt temperature; a large decease in viscosity is obtained at low melt temperature. Compared with the mechanical properties obtained by conventional injection molding (CIM), the mechanical properties for vibration‐assisted injection molding (VAIM) samples were improved by changing the vibration frequency and vibration pressure amplitude. Injected at constant low vibration pressure amplitude, the VAIM sample prepared at high vibration frequency shows large elongation at break; injected at constant low vibration frequency, the VAIM sample prepared at high vibration pressure amplitude shows greatly improved yield strength. The above two VAIM processing routes produce different VAIM samples with different fracture behaviors; a distinct layered structure for VAIM samples was observed by SEM.     

Correlation of the Morphological and Mechanical Properties of a Biodegradable Blend Based on Polylactic Acid

A series of binary and ternary blends composed of polylactic acid (PLA), low-density polyethylene (LDPE), and chitosan (CS) were prepared and characterized in terms of their morphological and mechanical properties. The mechanical properties of the prepared blends, including tensile properties and impact strength, were compared with neat PLA. In addition, the effect of incorporation of maleic anhydride-grafted linear low-density polyethylene (LLDPE-g-MA) as a compatibilizing agent, and the order of mixing on the mechanical and morphological properties of the ternary blends were also studied. It was observed that addition of CS enhanced the stiffness of PLA/LDPE blends while it decreased the toughness and tensile strength. It was demonstrated that addition of LLDPE-g-MA, up to 10 wt%, had no significant compatibilizing effect. However, the mechanical results indicated that when 15 wt% of LLDPE-g-MA was loaded, it started to play a compatibilizing role and caused an improvement in the toughness properties of ternary blend.     

Morphology and Properties of Poly(vinyl alcohol)/MMT Nanocomposite Prepared by Solid-state Shear Milling (S3M)

Poly(vinyl alcohol) (PVA)/montmorillonite (MMT) nanocomposites were prepared by combining solid-state shear milling (S³M) technology with melt intercalation. Compared with the composite obtained by simple melt intercalation, more MMT layers were exfoliated and apparently oriented along the injection molding direction in the nanocomposite prepared by combining S³M technology and melt intercalation, which greatly increased the orientation degree of MMT, resulting in the greater interactions between PVA and MMT layers. Simultaneously, this also promoted the orientation of PVA molecules and produced effective nucleation of the crystallization of PVA. Consequently, the thermal stability and mechanical properties of PVA were obviously improved. For instance, when the MMT content was 3 wt%, the tensile strength and modulus of the nanocomposite with MMT prepared by S³M were 98.9 MPa and 3.1 GPa, respectively, increasing by 52% and 63.2% compared with PVA.     

Study on the Structure and Properties of UHMWPE/Epoxy Resin Composite Fiber

The preparation, crystallization behavior, and fiber structure and properties of ultrahigh molecular weight polyethylene (UHMWPE) epoxy resin composite fiber were studied by means of differential scanning calorimeter (DSC), X‐ray diffraction (XRD), Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and tensile testing. The morphology showed a different behavior from pure polyethylene (PE) fiber. The fiber mechanical properties, creep behavior, and thermal properties of UHMWPE fiber can be improved by adding epoxy resin. It's believed that the epoxy can serve as a physical cross‐linking agent to limit the motion or migration of PE molecules and consequently improve the fiber creep property. However, when the content of epoxy resin is higher than 5 wt%, all of the behavior and properties deteriorate.     

Investigation on Changes in the Miscibility,Morphology, Rheology and Mechanical Behavior of Melt Processed Cellulose Acetate through Adding Polyethylene Glycol as a Plasticizer

Polyethylene glycol (PEG 200) was used as an eco-friendly plasticizer for preparing thermoplastic cellulose acetate (CA) by a twin-screw extruder. The plasticization efficiency of PEG 200 was compared with that of triethyl citrate (TEC). The interaction between polyethylene glycol and CA was investigated by Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). Both FT-IR and DSC proved that PEG 200 could form stable and strong hydrogen bonds with CA molecules. Scanning electron microscopy (SEM) revealed that the CA granules were completely disrupted during the extrusion and a continuous and homogeneous phase was observed. The PEG 200-plasticized cellulose acetate (PCA) showed greater viscosity reduction than TEC-plasticized cellulose acetate (TCA) at the same additive levels. Furthermore, the Izod-notched impact strength and elongation at break of PCA were higher than those of TCA. The tensile strength, Izod-notched impact strength and elongation at break of PCA containing 25 wt% PEG 200 reached 31.6 MPa, 20.9 KJ/m² and 80.5%, respectively, as compared to 39.2 MPa, 10.9 KJ/m² and 32.3% for 25 wt% TEC plasticized CA.     

Decomposition behavior and properties of Sn-9Zn-1Bi lead-free solder alloy with copper content

Copper was chosen as quaternary additions in the range of 1–5 wt% to the ternary alloy Sn-9Zn-1Bi lead-free solder alloy. X-ray diffraction analysis, scanning electron microscopy and differential thermal analysis have been carried out. Resistivity, Vickers microhardness and yield strength have been measured. The results showed that formation of Cu-Sn intermetallic compounds takes place due to additions of Cu, which affected the electrical resistivity and improved mechanical properties of this alloy. Also, addition of copper upto 2 wt% caused grain refinement and decreased the melting point of this alloy by 2 °C.     

Effect of an In-Situ Nucleating Agent on the Polymorphs and Mechanical Properties of Isotactic Polypropylene

The influence of glutaric acid (GA)/cadmium hydroxide [Cd(OH)₂] mixtures on the crystallization and properties of isotactic polypropylene (iPP) was investigated by means of differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), polarized light microscopy, and mechanical tests. It was found that the β-crystalline form was produced in the samples containing 0.15 wt% GA and more than 0.17 wt% Cd(OH)₂. The content of β-crystalline form was maximum, i.e. K_DSC = 65.4% and K_WAXD = 71.4%, when the sample was doped with GA (0.15 wt%)/Cd(OH)₂ (0.20 wt%) (the molar ratio of GA:Cd(OH)₂ was 1:1.2). It was also found that GA/Cd(OH)₂ mixtures not only induced the β-crystalline form but also made spherulites smaller. The results of mechanical tests showed that the toughness of iPP was greatly improved by bicomponent nucleator, while the stiffness decreased a little. Fourier transform infrared spectroscopy analysis indicated that an “in-situ” chemical reaction occurred between GA and Cd(OH)₂ during melt blending, yielding an effective β nucleator (cadmium glutarate).     

Effect of ionic liquid on the properties of poly(vinylidene fluoride)-based gel polymer electrolytes

Poly(vinylidene fluoride)-based polymer electrolytes using ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsufonyl)imide as the plasticizer were prepared by solution casting method. The effects of the solvent evaporation temperature (SET) and ionic liquid content (ILC) on the properties and structures of the polymer electrolytes were investigated by characterization of scanning electron microscope (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry, as well as mechanical and ionic conductivity test. It was confirmed that both SET and ILC had significant influence on the morphology, degree of crystallinity, mechanical properties, and ionic conductivity of the prepared polymer electrolytes. With ILC of 40 %, an excellent polymer electrolyte can be obtained at SET of 60 °C, which exhibited ionic conductivity up to ca. 10^?4 S/cm at room temperature, accompanied by excellent tensile strength of 22.8 MPa and elongation at break of 540 %.     

Styrene Butadiene Rubber/Epoxidized Natural Rubber (SBR/ENR50) Nanocomposites Containing Nanoclay and Carbon Black as Fillers for Application in Tire-Tread Compounds

Nanocomposite vulcunizates based on a SBR/ENR50 (50/50%wt) rubber blend containing nanoclay (5 or 10 phr) with and without carbon black (CB 20 phr) were prepared by melt blending in an internal mixer. The compound containing 35 phr carbon black (only) was prepared as a reference sample. Microstructure of nanocomposite samples was investigated by using X-ray diffraction (XRD), melt rheo-mechanical spectroscopy (RMS), and scanning electron microscopy (SEM). The XRD patterns revealed that the distance between the clay layers were increased by adding CB to the nanocomposite samples; they caused better diffusion of chains between the layers and resulted in an intercalated structure. The RMS results also indicated the formation of the filler-filler networks. SEM images of fracture surfaces showed the presence of much roughness in the samples containing both nanoclay and CB compared to the other samples. The results obtained from application of the Flory–Rhener equation showed a high crosslink density for the sample with 10 phr nanoclay and 20 phr CB. Dynamic mechanical behavior, mechanical properties, and abrasion resistance of the nanocomposites were evaluated. The results indicated that the sample containing 10 phr nanoclay and 20 phr CB had an increased dynamic elastic modulus, reduced maximum loss factor (tanδ)_max,, and an improved tensile strength and abrasion resistance compared to the reference sample. Also, this sample showed the lowest maximum loss factor, at 50–60°C, so it can be a candidate for tire-tread application.     

Mechanical and Thermal Performance of High-Density Polyethylene/Alumina Nanocomposites

High-density polyethylene (HDPE) nanocomposites reinforced with pristine and vinyltrimethoxysilane (VTMS)-treated alumina nanoparticles of 2, 4, and 6 wt% were melt-compounded in a twin-screw extruder followed by injection molding. Their structure, thermal and mechanical behaviors were studied. Fourier transform infrared (FTIR) spectra showed that VTMS was successfully covalently grafted to the alumina nanoparticles. The X-ray diffraction (XRD) patterns indicated that the alumina nanoparticle additions broadened the characteristic peak width of HDPE, indicating that they reduced the crystallite size of HDPE. The heat deflection temperature and thermogravimetric analyses demonstrated that the dimensional and thermal stability of HDPE were enhanced markedly by adding pristine and silane-treated alumina nanoparticles. The alumina nanoparticle additions were also beneficial in enhancing Young's modulus and yield strength of HDPE. The reinforcing effect was particularly apparent in the silane-treated nanocomposites due to improved filler–matrix interactions.     

Self-Reinforced High-Density Polyethylene Prepared by Low Frequency Vibration-Assisted Injection Molding. II: Microstructure Investigation

Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and wide angle X-ray diffraction (WAXD) were employed to study the microstructure of self-reinforced high-density polyethylene (HDPE) prepared by conventional injection molding (CIM) and a low frequency vibration-assisted injection molding (VAIM). SEM micrographs following permanganic etching showed the self-reinforcement of HDPE is mainly due to the existence of shish-kebab morphology within the core region for VAIM-processed HDPE samples. Pronounced molecular alignment was identified by the WAXD data. An approximate 9% increase in the crystallinity was confirmed by DSC. Both preferred molecular orientation and increased crystallinity serve to yield stronger VAIM-processed injection moldings.     

Preparation and Characterization of Linear Low Density Polyethylene/Carbon Nanotube Nanocomposites

Linear low‐density polyethylene (LLDPE)/multiwalled carbon nanotube (MWNT) nanocomposites were prepared via melt blending. The morphology and degree of dispersion of nanotubes in the polyethylene matrix were investigated using scanning electron microscopy (SEM). Both individual and agglomerates of MWNTs were evident. The rheological behavior and mechanical and electrical properties of the nanocomposites were studied using a capillary rheometer, tensile tester, and Tera ohm‐meter, respectively. Both polyethylene and its nanocomposites showed non‐Newtonian behavior in almost the whole range of shear rate. Addition of carbon nanotubes increased shear stress and shear viscosity. It was also found that the materials experience a fluid‐solid transition below 1 wt% MWNT. Flow activation energy for the nanocomposites was calculated using an Arrhenius type equation. With increasing nanotube content, the activation energy of flow increases. A decrease of about 7 orders of magnitude was obtained in surface and volume resistivity upon addition of 5 wt% MWNT. In addition, a difference between electrical and rheological percolation thresholds was observed. The results confirm the expected nucleant effect of nanotubes on the crystallization process of polyethylene. A slight increase in Young's modulus was also observed with increasing MWNT content.