The non-uniform phase structure in blend fiber. I. Non-uniform deformation of the dispersed phase in melt spinning

By melt spinning of incompatible polymer blends, the deformation of the dispersed phase was investigated in the fiber spinning process, for polypropylene/polystyrene (PP/PS) blend fiber and low density polyethylene/polyamide 6 (LDPE/PA6) blend fiber, respectively. Two kinds of the take-up fiber all exhibit the matrix fibrillar morphology, but with the opposite morphology. For PP/PS take-up fiber, the dispersed PS fibrils were finer in the core than near the surface. On the contrary, the dispersed PA6 fibrils were finer near the surface than in the core for LDPE/PA6 take-up fiber. However, for the special fiber in which the extensional flow was absent, there was the uniform morphology in either PP/PS or LDPE/PA6. Thus, fibrils’ non-uniform deformation, occurred in the drawing process, was considered to be due to the radial non-uniform processing conditions across the spin-line cross-section. The distribution of fibrils’ diameter was also investigated on the whole cross section. Rheological properties of each component were measured by the capillary rheometer. The non-uniform phase structure in blend fiber is a new phenomenon in the extensional flow.     

Structure,electrical and mechanical properties of polyamide 66/acid-treated MWCNT composite films prepared by solution mixing in the presence of nonionic surfactant

Two different sets of polyamide 66(PA66)-based composite films containing 2.0-10.0 wt% acid-treated multiwalled carbon nanotubes (MWCNT) were manufactured by solution mixing and casting method in the presence or absence of a nonionic surfactant. For the improved dispersion and interfacial interaction of MWCNTs in the PA66 matrix, carboxylic acid-functionalized MWCNTs were prepared by the acid-treatment of pristine MWCNTs. The uniform dispersion of the acidtreated MWCNTs in the PA66 matrix was confirmed from FE-SEM images of the fractured composite film surfaces. DSC thermograms supported that the acid-treated MWCNTs served as nucleating agents for the melt-crystallization of PA66 in both composite films prepared with/without the addition of the surfactant. The electrical and tensile mechanical properties of the composite films prepared with the surfactant were ~20 % higher than those of the composite films manufactured without the surfactant. For both composite films, sheet resistivity and tensile mechanical properties were found to be highly decreased and increased, respectively, with the increment of the acid-treated MWCNT content.     

Effects of Chemical Functionalization of MWCNTs on the Structural and Physical Properties of Elastomeric Copolyetherester-based Composite Fibers

Elastomeric copolyetherester (CPEE)-based composite fibers incorporating various neat and functionalized multiwalled carbon nanotubes (MWCNTs) were prepared through a conventional wet-spinning and coagulation process. The influence of functionalized MWCNTs on the morphological features, and the thermal, mechanical properties and electrical conductivity of CPEE/MWCNT (80/20, w/w) composite fibers were investigated. FE-SEM images show that a composite fiber containing poly(ethylene glycol)-functionalized MWCNTs (MWCNT-PEG) has a relatively smooth surface owing to the good dispersion of MWCNT-PEGs within the fiber, whereas composite fibers including pristine MWCNTs (p-MWCNT), acid-functionalized MWCNTs (a-MWCNT), and ethylene glycol-modified MWCNTs (MWCNT-EG) have quite a rough surface morphology owing to the presence of MWCNT aggregates. As a result, the CPEE/MWCNT-PEG composite fiber exhibits noticeably increased thermal and tensile mechanical properties as well as a faster crystallization behavior, which stems from an enhanced interfacial interaction between the CPEE matrix and MWCNT-PEGs.     

Effects of mechanical strain on the electric conductivity of multiwalled carbon nanotube (MWCNT)/polyurethane (PU) composites

Conducting polymers have been under development for more than thirty years as replacements for metals in various applications, such as fuel cells, solar cells, actuators, etc. In this study, we investigate conducting polymer composites and attempt to fabricate composite polyurethane/multiwalled carbon nanotubes. The multiwalled carbon nanotubes (MWCNTs) were acid-treated to add functional groups such as -OH or -COOH so they could then be chemically bonded to diisocyanate to form a urethane linkage. Because they have fewer impurities and reduced surface roughness (as confirmed by TEM micrographs), acid-treated MWCNTs can be better dispersed in a polyurethane (PU) matrix than untreated MWCNTs, and acid-treated MWCNTs exhibit better adhesion with the PU matrix, as well. In addition, the conductance test of MWCNT/PU films as a function of elongation showed that the conductance of the acid-treated MWCNT/PU increased up to a certain % elongation, while that of the untreated MWCNT/PU decreased monotonically with % elongation.     

Enhanced mechanical and thermal properties of hybrid graphene nanoplatelets/multiwall carbon nanotubes reinforced polyethylene terephthalate nanocomposites

The effects of graphene nanoplatelets (GNP) and multiwall carbon nanotube (MWCNT) hybrid nanofillers on the mechanical and thermal properties of reinforced polyethylene terephthalate (PET) have been investigated. The nanocomposites were melt blended using the counter rotating twin screw extruder followed by injection molding. Their morphology, mechanical and thermal properties were characterized. Combination of the two nanofillers in composites formulation supplemented each other which resulted in the overall improvement in adhesion between fillers and matrix. The mechanical properties and thermal stability of the hybrid nanocomposites (PET/GNP1.5/MWCNT1.5) were significantly improved compared to PET/GNP3 and PET/MWCNT3 single filer nanocomposites. However, it was observed that GNP was better in improving the mechanical properties but MWCNT resulted in higher thermal stability of Nanocomposite. The transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) revealed uniform dispersion of the hybrid fillers in PET/GNP1.5/MWCNT1.5 nanocomposites while agglomeration was observed at higher filler content. The MWCNT prevented the phenomenal stacking of the GNPs by forming a bridge between adjacent GNP planes resulting in higher dispersion of fillers. This complimentary geometrical structure is responsible for the significant improvement in the thermal stability and mechanical properties of the hybrid nanocomposites.     

Facile fabrication of carbon nanotubes/polystyrene composite nanofibers for high-performance electromagnetic interference shielding

Polystyrene (PS) composites with nanofibrous structure consisting of multi-walled carbon nanotubes (MWCNTs) with 0-10 wt.% of nanofiller have been fabricated via electrospinning technique. The surface morphology and thermal properties of the composites were evaluated by scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA). The SEM analysis of the composite nanofibers samples revealed that the average diameter of the nanofibers increases with increasing MWCNTs content. The resultant MWCNTs/PS composite nanofibers diameters were in the range of 391±63 to 586±132 nm. The thermal stability of composites was increased after addition of MWCNTs to PS matrix. The electrical conductivity of the composites with different weight percentage of MWCNTs was investigated at room temperature. Electrical conductivity of MWCNTs/PS composite nanofiber followed percolation theory having a percolation threshold V _c= 0.45 vol% (~0.75 wt. %) and critical exponent q=1.21. The electrical conductivity and thermal properties confirmed the presence of good dispersion and alignment MWCNTs encapsulated within the electrospun nanofibers. The electromagnetic interference (EMI) shielding effectiveness of the MWCNTs/PS composites was examined in the measurement frequency range of 8.2-12.4 GHz (X-band). The total EMI shielding efficiency of MWCNTs/PS composite nanofibers increased up to 32 dB. The EMI shielding results for MWCNTs/PS composite nanofibers showed that absorption loss was the major shielding mechanism and reflection was the secondary mechanism. The present study has shown the possibility of utilizing MWCNTs/PS composite nanofibers as EMI shielding/absorption materials.     

Effects of date palm leaf fiber on the thermal and tensile properties of recycled ternary polyolefin blend composites

This work investigated the effects of date palm leaf fiber (DPLF) content on the thermal and tensile properties; and morphology of compatibilized polyolefin ternary blend. Recycled polyolefin ternary blend consisting of low density polyethylene (RLDPE), high density polyethylene (RHDPE) and polypropylene (RPP) were fabricated at different parts per hundred resin (phr) of DPLF. Maleic anhydride grafted polyethylene (MAPE) was used as compatibilizer to enhance the adhesion between filler and polymer matrix. The composites were prepared using melt extrusion and tests samples were produced via injection molding process. Thermal conductivity results showed that as much as 11 % reduction in thermal conductivity was achieved with the incorporation of 30 phr DPLF. Highest tensile strength was observed with the incorporation of 10 phr DPLF. The elongation at break was reduced with the addition of DPLF due to impediment of chain mobility by the fillers. Initial degradation temperature increased with the addition of DPLF. Hence, it is concluded that DPLF can be used to develop green and thermally insulating composites. It is hoped that the present results will stimulate further studies on the thermally insulative materials based on natural fibers reinforced polymer composites for applications in the building industries.     

Matrix-fibril morphology development of polypropylene/poly(butylenes terephthalate) blend fibers at different zones of melt spinning process and its relation to mechanical properties

Different shapes of dispersed phase such as sphere, laminar and fibrillar can form in the matrix phase of polymer blends. Production of blend fibers in melt spinning process can result more effective in fibrillar phase morphology formation than in other processes. In this research, the matrix-fibril morphology development during the melt spinning of polypropylene/poly(butylenes terephthalate) was studied. The shapes of blend dispersed phase collected from different zones of the melt spinning line were evaluated by scanning electron micrographs (SEM) and rheological mechanical spectra (RMS). The results showed that fibrillar shape could not be created in the PP/PBT blend fiber samples exited from the spinneret orifice (gravity spun fibers) at low contents (5 percent) of the PBT dispersed phase. However, a complete fibrillar structure was formed in all the as-spun PP/PBT blend fiber samples (melt drawn). The rheological evaluations confirmed a network structure resulting from fibril formation for the samples with high contents (20–40 %) of the PBT dispersed phase and the formation of spherical shape with low contents (5–10 %) of the PBT dispersed phase in matrix of the blend fibers. It was observed that the flow fields of processing zones and blend ratio, in producing the blend fibers, have intensive effects on morphological variations; besides there was a strong relation between the mechanical and morphological properties.     

Fabrication and Characterization of Poly(L-lactic Acid) Fiber Mats Using Centrifugal Spinning

Polylactic acid (PLA) fine fibers and multi walled carbon nanotube (MWCNT) reinforced PLA fine fiber composites were developed utilizing a centrifugal spinning process. Chloroform and chloroform combined with dimethylformamide (DMF) were used to prepare solutions with varying concentrations of PLA and MWCNTs. The optimum spinning conditions to produce PLA fibers and its composites were determined. The morphology of the fibers was analyzed using scanning electron microscopy. In addition, X-ray diffraction analysis and thermo-physical characterization was conducted using thermogravimetric analysis and differential scanning calorimetry. PLA fibers with an average diameter of 481 nanometers and PLA/MWCNT fibers with an average diameter of 358 nanometers were obtained. A decrease in the crystallinity of the fibers was observed when compared to bulk PLA values.     

Thermal properties of Poly(trimethylene terephthalate)/Poly(ethylene terephthalate) melt blends

The thermal behavior, morphology, ester-interchange reaction of Poly(trimethylene terephthalate) (PTT)/Poly(ethylene terephthalate) (PET) melt blends were investigated over the whole composition range(xPTT/(1-x)PET) using a twinscrew Brabender. The melt blends were analyzed by differential scanning calorimetry (DSC), nuclear magnetic resonance spectroscopy (¹³C-NMR), and scanning electron microscopy (SEM). Single glass transition temperature (T _g ) and cold crystallization temperature (T _cc ) were observed in all melt blends. Melt blends were found to be due to the ester-interchange reaction in PTT/PET blend. Also the randomness of copolymer increases because transesterification between PTT and PET increases with increasing blending time. This reaction increases homogeneity of the blends and decreases the degree of crystallinity of the melt blends. In PTT-rich blends, mechanical properties decrease with increase of PET content compared with that of pure PTT. And, in PET-rich blends, tensile modulus decreases with increase of PTT content, but tensile strength and elongation is similar to that of pure PET.     

The non-uniform phase structure in blend fiber. II. The migration phenomenon in melt spinning

The migration phenomenon was investigated in polypropylene/polystyrene (PP/PS) blend fiber and low density polyethylene/polyamide 6 (LDPE/PA6) blend fiber. The migration of fibrils in melt spinning was evaluated by the variation of fibrils’ area ratio over the cross section of blend fiber. In PP/PS blend fiber, the dispersed PS deformed into many highly oriented fibrils in the PP matrix, and PS fibrils migrated towards the surface of the take-up fiber in the fiber spinning process. On the contrary, PA6 fibrils migrated into the core of the take-up fiber, while the dispersed PA6 deformed into many highly oriented fibrils in the LDPE matrix for LDPE/PA6 blend fiber. Otherwise, no migration phenomenon was observed in the special fiber that was prepared without any drawing, neither in PP/PS nor in LDPE/PA6. Therefore, in the fiber spinning process, the migration phenomenon actually occurred mainly in the drawing process, which is the non-isothermal uniaxial extensional flow. Comparing with migration mechanisms in the shear flow, the migration phenomenon in melt spinning was probably due to the radial non-uniform extensional stress, the extensional viscosity.     

The variation of fibrils’ number in the sea-island fiber -low density polyethylene/polyamide 6-

In melt spinning of low density polyethylene/polyamide6 (LDPE/PA6), fibrils’ number in LDPE/PA6 blend fiber is calculated at different take-up velocity. Firstly, PA6 fibrils are dispersed in the LDPE matrix in LDPE/PA6 blend fiber (55:45, weight ratio). The number of PA6 fibrils increases with an increase of the take-up velocity. Because the shorter processing time suppresses the coalescence at the high take-up velocity, it causes an increase of PA6 fibrils. Besides, the irregular shape of PA6 fibrils’ cross section also confirms fibrils’ coalescence. Secondly, LDPE fibrils are dispersed in the PA6 matrix in LDPE/PA6 blend fiber (6:94, weight ratio). However, the number of LDPE fibrils doesn’t change no matter how the takeup velocity is. In case of LDPE/PA6 (6:94) blend fiber, the low weight ratio of the dispersed LDPE causes the absence of fibrils’ coalescence, so fibrils’ number does not change. In conclusion, the variation of fibrils’ number implies the existence of the coalescence phenomenon in the fiber spinning process. The variation of fibrils’ number in the sea-island fiber is of practical importance for manufacturing the micro-fine fiber, and is a method to investigate the coalescence behavior in the extensional flow.     

Processing and characterization of liquid crystalline copoly-(ethylene terephthalate-co-2(3)-chloro-1,4-phenylene terephthalate)/polycarbonate blends

Liquid crystalline (LC) poly(ethylene terephthalate-co-2(3)-chloro-1,4-phenylene terephthalate) (50/50, mole/mole) [PECPT] was synthesized and blended with polycarbonate (PC). LC properties of PECPT and thermal, morphological, and rheological behaviors of the PECPT/PC blend were studied. PECPT showed the nematic LC phase and much longer relaxation time than poly(ethylene terephthalate) (PET). The apparent melt viscosity of PECPT was one third of that of PET. An abrupt torque change was observed during the blending process due to the orientation of LC domains. For the blends containing 10∼30 wt% of PECPT, the complex viscosities were higher than that of PC. As PECPT content increases above 40 wt%, shear thinning was observed. The lowest complex viscosity was obtained at 40∼50 wt%. Transesterification of PECPT and PC was confirmed by the selective chemical degradation of carbonate groups in PC.     

Enhanced mechanical and thermal properties of carbon fiber composites with polyamide and thermoplastic polyurethane blends

In this article, we demonstrated the preparation of carbon-fiber-reinforced composites using a polyamide 6 (PA6)/thermoplastic polyurethane (TPU) blend, in which the addition of TPU resulted in superior mechanical performances and increased thermal stability. According to various characterization techniques, these results are attributed to an enhanced adhesion and a homogeneous dispersion of long-carbon-fibers (LCFs) with TPU sizing in blended polymer matrix. Above all, dynamic-mechanical thermal analysis (DMTA) measurements clearly show that the dynamic storage modulus (E') of the blend composites is increased by threefold with temperature ranges below and above the glass transition temperature. The presence of LCFs in TPU systems induces effective fiber orientation, exhibiting simultaneous improvements in the tensile strength, flexural strength, and thermal stability.     

Use of acetylated softwood kraft lignin as filler in synthetic polymers

Partially acetylated softwood kraft lignin (ASKL) is used as filler in synthetic polymers such as LDPE, PP, PS and PET. ASKL/synthetic polymer composites are prepared by melt-blending and compression molding with ASKL content up to 50.0 wt%. The chemical and physical properties of ASKL/synthetic polymer composites are also investigated. TGA results show that ASKL is more thermally stable than SKL up to 200 °C. FTIR spectra demonstrate a formation of free volume by crystallization of LDPE in ASKL/LDPE composite. DSC results show that the glass transition temperature of ASKL decreased by acetylation, and ASKL/synthetic polymer composites (50/50 w/w) have a single glass transition. The AFM images of ASKL/synthetic polymer composites show no significant phase separation. Young’s moduli of ASKL/synthetic polymer composites increased with ASKL content in some extents. Tensile strength and breaking strain of ASKL/PET composite are almost retained in spite of the addition of ASKL as a result of a contraction in free volume or densification.     

Optimization of molecular structure of polythiophene-graft-PMMA for effective compatibilization of SAN/MWCNT composite with superior mechanical properties

A new compatibilizer, P3HT-g-PMMA with controlled graft density and degree of polymerization of PMMA graft, has been synthesized for preparation of poly(styrene-co-acrylonitrile) (SAN)/multi-walled carbon nanotube (MWCNT) composites with superior mechanical properties. Fluorescence emission and Raman spectra reveal that the π-π interaction between polythiophene backbone of the compatibilizer and the surface of MWCNT is more effective as the graft density of PMMA in the compatibilizer is decreased while the degree of polymerization of PMMA is increased. Since FE-SEM observation also shows that the use of compatibilizer with higher degree of polymerization of PMMA graft yields well-dispersed MWCNTs in composites, it is concluded that the compatibilizer with lower graft density and higher degree of polymerization of PMMA graft is the most effective for reinforcing SAN with MWCNT.     

Development of amino acid-modified PET/PA6 segmented pie bicomponent spunbonded microfiber nonwoven for bilirubin affinity adsorption

A novel affinity membrane based on PET/PA6 segmented pie bicomponent spunbonded microfiber nonwoven (PET/PA6 SBSNW) was developed for bilirubin adsorption. PET/PA6 SBSNW was initially fabricated as microfiber nonwoven fabric, and was then ammoniated with ethylenediamine (ETDA). Finally, amino acids as affinity ligands were immobilized on the ammoniated PET/PA6 SBSNW. The amino acid-modified PET/PA6 SBSNW was applied to adsorb bilirubin, and the effects of pH, temperature, species of affinity ligands, and time were investigated. The results showed that amino acid-modified PET/PA6 SBSNW has decent adsorption performance, and adsorption capacity of PET/PA6 SBSNW-Lys peaked at 388.35 mg/g.     

Mechanical properties of MA compatibilised NR/CS blends

This article describes the effect of compatibilising agent on natural rubber (NR)/chitosan (CS) blends. Maleic anhydride (MA) was used as the compatibiliser. The mechanical properties such as tensile strength, elongation at break, and modulus at various elongations of compatibilised NR/CS blends were studied by universal testing machine and the surface hardness was studied by Shore A Durometer. The interaction between the two components was analyzed by calculating the fraction of bound rubber in the blend from the relative weight loss data in benzene as the solvent. The incorporation of MA into NR/CS blends improved tensile strength up to 15 % of chitosan in the blend and above which it decreased. The elongations at break of the MA treated blends decreased and a drastic enhancement of surface hardness was observed by the addition of MA in the blend. The interfacial reactivity (adhesion) of NR/CS blends was studied as a function of the incorporation of compatibiliser by the estimation of relative weight loss. The data revealed an increase in the interfacial adhesion between NR and CS, resulting in an improvement of the gel fraction (%) in the blend. The effect of thermal ageing on the mechanical properties of the compatibilised blends was also studied. The morphology of the compatibilised blends was studied by scanning electron microscopy and it shows a continuous morphology.     

Improvement of high-velocity impact properties of anisogrid stiffened composites by multi-walled carbon nanotubes

The present study represents the influence of adding different weight fractions (0, 0.1, 0.25 and 0.4 wt.%) of multi-walled carbon nanotubes (MWCNT) on the high velocity impact behavior of anisogrid stiffened composite (AGSC) plates. AGSC plates were fabricated through hand lay-up method where E-glass woven fabrics and unidirectional carbon fiber rovings were used as fibrous reinforcement of ribs and skin, respectively. High velocity impact test was performed on these plates by cylindrical projectile with conical nose. Obtained results revealed that the maximum improvement of the high velocity impact properties of AGSC plates were obtained through addition of 0.4 wt.% of MWCNTs. Field emission scanning electron microscopy (FESEM) examinations of the fracture surfaces clearly indicated the improvement in the interfacial adhesion between the fibers and epoxy matrix in the case of the nanocomposite specimens. Also, it was observed that the addition of MWCNTs to the AGSC specimens led to reduce the damage area and increased the damage tolerance, considerably.     

Si-Al hybrid effect of waterborne polyurethane hybrid sizing agent for carbon fiber/PA6 composites

The interface of fiber-reinforced composites has remained a vexing problem that limits the use of the excellent properties of carbon fiber (CF) in composite applications. In the present study, waterborne polyurethane (WPU) hybrid sizing agents were prepared to improve the performances of CFs and the interface strength of CF/PA6 composites. The structural and mechanical properties of the single-CF and CF/PA6 composites were systematic investigated. The results showed that the mechanical properties of the CF/PA6 composites were significantly improved by adding of WPU hybrid sizing agent. The tensile and flexural strengths of the WPU/SiO₂/Al₂O₃ hybrid sizing agent treated CF/PA6 composites were increased by 24.0 % and 25.7 % than those of no-sizing treated CF/PA6 composites, respectively.