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The effects of ions on the structures and properties of poly(vinyl alcohol) films were systematically studied using various metal salts. Although cations play an important role, the data obtained in this study demonstrated that the strong ion–dipole interactions between anions and poly(vinyl alcohol) chains also have a significant impact on crystallinity and glass transition temperature. For the first time, the study revealed that the impact of the added salts follows the Hofmeister series. Investigations of various bromine salt cations revealed that Li+ is more effective at disrupting the water structure than either Na+ or K+. Further experiments using lithium salts with various anion species verified that lithium salts play an important role in determining the crystallinity and hydrogen bonding within aqueous poly(vinyl alcohol) and therefore affect the dynamic mechanical properties of films. This phenomenon clearly follows the order LiClO4 > LiI > LiBr > LiNO3 > LiCl, which corresponds to the Hofmeister series. The salt addition affects the structure and properties of poly(vinyl alcohol) films as it reduces the hydrogen bonding in PVA chains and decreases the crystallinity. Consequently, the Tg shifts to low temperatures, and the modulus beyond Tg decreases markedly. This study confirmed that the impact of bromine salts on the structure and properties followed the order of Hofmeister series, i.e., Li+ > Na+ > K+. Although cations play an important role, the data obtained also demonstrated that the strong ion–dipole interactions between anions and PVA chains have a significant impact on the crystallinity and Tg.

Rheological properties for binary polyolefin blends composed of linear low-density polyethylene (LLDPE) and long-chain branched polypropylene (LCB-PP), in which LCB-PP is the dispersed phase, were studied. Even though LCB-PP was in the dispersed phase, the blend showed marked strain-hardening behavior in the transient elongational viscosity. The deformed LCB-PP droplets acted as “rigid fibers” during the elongational flow owing to its strain-hardening behavior. Consequently, the blend behaved like a fiber-dispersion system and thus exhibited the enhanced elongational viscosity, originated from excess deformation of LLDPE located between fibrous LCB-PP droplets under the elongational flow. Under shear flow, the primary normal stress difference was not enhanced by the addition of LCB-PP. This is reasonable because LCB-PP droplets oriented to the flow direction did not provide excess deformation of a continuous phase greatly.

The transient uniaxial elongational viscosity for binary blends composed of polypropylene (PP) and low-density polyethylene (LDPE) was evaluated. A strain hardening behavior is detected for the blends, although LDPE is a dispersed phase. This behavior is attributed to LDPE dispersion deformation; the LDPE forms rigid fibers because of strain hardening. Rheological properties are calculated numerically by the Phan–Thien Tanner model by assuming a symmetric geometry with a periodic structure. Based on the simulation, we propose an appropriate LDPE to modify the processability of PP, for which the strain hardening in the elongational viscosity is required. Transient elongational viscosity for polypropylene (PP)/low-density polyethylene (LDPE) blends was evaluated. Because deformed LDPE droplets act as rigid fibers due to its strain hardening, the blends show a strain hardening behavior. The growth curves are, however, affected by their viscosity ratio. These behaviors are calculated by the Phan–Thien Tanner model by assuming a symmetric geometry with a periodic structure. Based on the simulation, we propose an appropriate LDPE to modify the processability, at which the strain hardening in the elongational viscosity is required.

The effects of the ultra-high-molecular-weight (UHMW) component of polypropylene (PP) on its rheological properties, crystallization behavior, and solid-state mechanical properties were investigated using various measurement techniques. The terminal relaxation time—determined by measuring the linear viscoelasticity—was increased by adding the UHMW component. The increase in the melt elasticity produced by adding the UHMW component was observed by measuring the steady-state shear flow, although the shear viscosity was not greatly affected. Owing to the long characteristic time of the Rouse relaxation of the UHMW component, PP with the UHMW component formed highly oriented structures through a shear-induced crystallization process. The addition of the UHMW component enhanced the orientation and regularity of crystalline structure for extruded films. Therefore, the Young′s modulus, yield stress, and strength were higher in the PP film containing the UHMW component than in one without the UHMW component, irrespective of the direction of tensile deformation.

In this study, Kraft lignin was esterified with phthalic anhydride and was served as reinforcing filler for poly(butylene succinate) (PBS). Composites with different ratios of PBS, lignin (L), modified lignin (ML) and kenaf core fibers (KCF) were fabricated using a compounding method. The fabricated PBS composites and its counterparts were tested for thermal, physical and mechanical properties. Weight percent gain of 4.5% after lignin modification and the FTIR spectra has confirmed the occurrence of an esterification reaction. Better thermo-mechanical properties were observed in the PBS composites reinforced with modified lignin and KCF, as higher storage modulus and loss modulus were recorded using dynamic mechanical analysis. The density of the composites fabricated ranged from 1.26 to 1.43 g/cm3. Water absorption of the composites with the addition of modified lignin is higher than that of composites with unmodified lignin. Pure PBS exhibited the highest tensile strength of 18.62 MPa. Incorporation of lignin and KCF into PBS resulted in different extents of reduction in tensile strength (15.78 to 18.60 MPa). However, PBS composite reinforced with modified lignin exhibited better tensile and flexural strength compared to its unmodified lignin counterpart. PBS composite reinforced with 30 wt% ML and 20 wt% KCF had the highest Izod impact, as fibers could diverge the cracking propagation of the matrix. The thermal conductivity value of the composites ranged from 0.0903 to 0.0983 W/mK, showing great potential as a heat insulator.

Adding polyethylene greatly affects the rheological response of isotactic polypropylene (PP) under uniaxial elongational flow. Though strain hardening in the transient elongational viscosity barely appeared in pure PP, we induced strain hardening by adding low-density polyethylene (LDPE) to PP, even though the blends showed a phase-separated structure. During elongational flow, LDPE droplets dispersed in the PP were deformed in the flow direction. Because LDPE shows marked strain hardening in the elongational viscosity, the deformed LDPE droplets behaved as rigid fibers as the strain increased. Consequently, the PP between the fibrous LDPE droplets experienced excess localized deformation, which increased the apparent elongational viscosity. Furthermore, adding the high-density polyethylene (HDPE) increased the drawdown force—defined as the force required for uniaxial stretching of a molten polymer in the nonisothermal condition. This behavior comes from the rapid crystallization of HDPE, which causes the deformed HDPE particles to act as rigid fibers in the molten PP and enhances the PP crystallization, which increases the elongational stress.

The effects of neutralizer species on the transparency of injection-molded plates were studied using isotactic polypropylene (PP) containing a crystal nucleating agent—i.e., 1,3:2,4-bis-o-(4-methylbenzylidene)-d-sorbitol (MDBS). A plate containing lithium stearate (StLi) was more transparent than one containing calcium stearate (StCa) when the MDBS content was 0.1 wt. %. The addition of StLi accelerated the formation of MDBS fibers and the crystallization of PP. However, when the MDBS content was 1.0 wt. %, StCa improved the transparency more effectively than StLi. These results indicate that the combination of an appropriate amount of MDBS and the correct neutralizer species is critical for enhancing the transparency of injection-molded PP plates.

The bonding strength of a hot-melt adhesive composed of polyamide 6 (PA6) and lithium bromide (LiBr) with a metal plate was evaluated. PA6 containing LiBr showed strong lap shear strength with a metal plate immediately after hot-melt adhesion above the melting point of PA6, e.g., 1.0 MPa between PA6/LiBr (90/10) and aluminum plates. Owing to the high adhesive strength, the cohesive failure and/or plastic deformation of PA6 was detected during lap shear strength measurements. In contrast, separation was achieved without any difficulty after moisture absorption with a low strength, e.g., 0.1 MPa between PA6/LiBr (90/10) and aluminum plates. Furthermore, there was no trace of the adhesive on the metal plate after peeling. Therefore, this smart hot-melt adhesive provides an easy-peeling nature only through exposure to humid conditions as a trigger, which can be employed for various applications such as high-performance masking films.

The present study focused on the effects of the addition of lithium salts such as LiI, LiBr and LiCl on the rheological properties of aqueous solutions containing 15 wt% poly(vinyl alcohol) (PVA). There was a plateau in the shear storage modulus in the low frequency region, demonstrating that such solutions have a network structure attributed to hydrogen bonding of the PVA. The value of the plateau modulus evidently decreased with temperature and with the addition of lithium salts. The experimental results also demonstrated that the anion species in the salt plays an important role in determining the rheological properties, including the magnitude of the plateau modulus. The iodide anion, which is classified as a “water-structure-breaker” ion in the Hofmeister series, effectively decreased both oscillatory shear moduli including the plateau modulus. However, the effect of adding LiI decreased at high temperatures, owing to the reduced extent of hydrogen bonding.

Thermoplastic vulcanizate (TPV) has excellent elastomeric properties and can be reprocessed multiple times. TPV is typically produced by using the dynamic vulcanization (DV) method in which rubber is crosslinked simultaneously with thermoplastics. Peroxide-crosslinked TPV can increase the compatibility between rubber and thermoplastics but loses its reprocessability due to excess crosslinking in the latter. In this work, we overcome this obstacle by using a two-step mixing method to prepare fully crosslinked elastomers of ethylene vinyl acetate copolymer (EVA) and natural rubber (NR). Each sample formulation was prepared with three different mixing methods for comparison: NR-DV, Split-DV, and All-DV. For NR-DV, NR was crosslinked prior to the addition of EVA together with the thermal stabilizer (TS). For Split-DV, a small amount of EVA and NR was crosslinked prior to the addition of EVA and TS. In the All-DV method, EVA and NR were crosslinked, and then TS was added. The appearance and processability of the samples were affected by the degree of crosslinking. NR-DV showed a non-homogeneous texture. Although the samples of the All-DV method appeared homogeneous, their mechanical and rheological properties were inferior to those of the Split-DV method. The mechanical properties of the Split-DV samples were not significantly changed after reprocessing 10 times. Therefore, Split-DV is the preferred method for TPV production.

We investigated the effect of lithium trifluoromethanesulfonate (LiCF3SO3) on the optical properties of poly (methyl methacrylate) (PMMA), known as a glassy transparent polymer. The absolute values of the stress-optical coefficients in both the glassy and rubbery states were found to be reduced by the addition of LiCF3SO3. Furthermore, the linear coefficient of thermal expansion of the blend containing 10 wt.% of LiCF3SO3 was lower than that of pure PMMA, suggesting that the birefringence caused by thermal expansion in laminated display systems would be greatly reduced. These results indicate that PMMA/LiCF3SO3 is an appropriate blend for optical films used for liquid crystal displays.

The effect of acetyl substitution on the optical properties of cellulose acetate (CA) was investigated in the present study, because a strong demand for advanced retardation films increases greatly these days. The hot-stretched films with high acetyl substitution had negative orientation birefringence, whereas those with low acetyl substitution had positive orientation birefringence with extraordinary wavelength dispersion. It should be noted that orientation birefringence hardly relaxed even after cessation of hot-stretching. The slow relaxation of crystal orientation was responsible for the anomalous optical anisotropy, as confirmed by two-dimensional X-ray diffraction. Moreover, the slow relaxation of orientation birefringence would greatly benefit the preparation of CA optical retardation films by hot-stretching, because it would simplify the precise control of retardation. The stress-optical coefficient in the glassy state was also evaluated, and was found to decrease with the degree of acetyl substitution. This is an attractive property for optical film applications.

We investigated the effects of two metal salts, lithium trifluoromethanesulfonate (LiCF3SO3) and lithium bromide (LiBr), on the glass transition temperature (Tg) of poly(methyl methacrylate) (PMMA). Both LiCF3SO3 and LiBr greatly enhanced the Tg of PMMA under dry conditions. However, once the sample films were exposed to humidity, the PMMA containing LiCF3SO3 absorbed a large amount of water, which acts as a plasticizer. As a result, the Tg shifted to a lower temperature, which limits the utility of this polymer in industrial applications. In contrast, the Tg of PMMA containing LiBr was minimally affected by the absorption of water. This phenomenon can be explained by the ion–dipole interactions with the small number of dissociated lithium cations. Tg of PMMA was greatly enhanced by introducing ion–dipole interaction between lithium cations and carbonyl groups in PMMA as pseudo crosslinking points.

The effect of the lithium trifluoromethanesulfonate (LiCF3SO3) addition on the structure and properties for binary blends of poly(methyl methacrylate) (PMMA) and a random copolymer composed of vinyl butyral and vinyl alcohol, that is denoted as PVB in this paper, was evaluated. Although PMMA and PVB are immiscible, the LiCF3SO3 addition enhances the compatibility/miscibility by the ion-dipole interaction between lithium cation and both polymer chains. Only single peak ascribed to the glass-to-rubber transition is detected in the tensile loss modulus curve for PMMA/PVB/LiCF3SO3 (70/30/20), although there are distinct double peaks for PMMA/PVB (70/30). This result demonstrates that the salt, LiCF3SO3, acts as a compatibilizer. Furthermore, the salt addition enhances the storage modulus in the glassy region and the heat resistance due to the high-temperature-shift of glass transition temperature. The blend containing LiCF3SO3 is highly transparent and shows a significantly small value of the stress-optical coefficient in the glassy state, which are required for various optical films used for display, such as polarizer protective film.

An immiscible blend of isotactic polypropylene (PP) and ethylene-butene-1 copolymer (EB) (PP/EB = 70/30) containing a small amount of N,N'-dicyclohexyl-2,6-naphthalene dicarboxamide as a nucleating agent for β-form crystals was prepared by T-die extrusion. We successfully prepared an extruded sheet in which the orientation of the PP molecules is perpendicular to the deformation of the EB particles, i.e., the β-form crystals of PP are predominantly oriented perpendicular to the flow direction of the sheet plane (the transverse direction, TD), whereas the EB droplets are strongly deformed in the flow direction. It should be noted that EB barely affects the crystalline form and orientation of PP. This extraordinary structure provides unique mechanical anisotropy. The tear strength of the TD sample is significantly enhanced by the anomalous crack propagation in the machine direction (MD). Moreover, the anisotropy in tensile properties, such as the Young’s modulus, yield stress, strain at break, and dynamic tensile modulus, is reduced. An immiscible blend of isotactic polypropylene (PP) and ethylene-butene-1 copolymer (EB) containing a small amount of N,N'-dicyclohexyl-2,6-naphthalene dicarboxamide as a nucleating agent to generate β-form crystals was prepared by T-die extrusion. We successfully prepared an extruded sheet in which the orientation of the PP molecules is perpendicular to the deformation of the EB particles. It is suggested that EB barely affects the crystalline form and orientation of PP. Since this sheet containing a large amount of β-form crystals exhibits an extraordinary structure, unique mechanical anisotropy is obtained.

We studied the selective localization of carbon nanofillers, such as multi-walled carbon nanotube (MWCNT) and graphene nanoplatelet (GNP), in immiscible polymer blends composed of polycarbonate (PC) and polyethylene (PE) or ethylene-propylene copolymer (EPR). It was found that the distribution state of the carbon nanofillers in the composites is greatly affected by the mixing temperature and the species of nanofillers. MWCNTs resided in the PE or EPR phase in the composites, which cannot be explained by the difference in the interfacial tension. A similar morphology was detected in the PC/GNP/PE composite prepared at 300 °C. In contrast, the PC/GNP/PE composite prepared at the low temperature (250 °C) and the PC/GNP/EPR composites have the carbon nanofillers mostly in the PC phase. The selective localization in the PE or EPR phase is attributed to the surface adsorption of PE or EPR chains on the carbon nanofillers, which is more obvious for PE and at the high mixing temperature. These results demonstrate that both the species of carbon nanofillers and the mixing temperature affect the carbon nanofiller distribution in the immiscible blends.

The effects of magnesium salts with various anion species on the structure and properties of a poly(vinyl alcohol) (PVA) film were studied. The glass transition temperature of the PVA film increased following the addition of a magnesium salt. Furthermore, the salt greatly enhanced the modulus and yield stress and reduced the crystallinity of the film. These effects were attributed to the strong ion–dipole interactions between the magnesium salts and the PVA chains. The strength of interaction, i.e., the reduction of segmental motions, depended on the anion species in the following order: Mg(ClO4)2, MgBr2, MgCl2, Mg(CH3COO)2, and MgSO4. The order corresponded to the Hofmeister series, which predicts the ability to break the structure of water.

We controlled the optical anisotropy of a solution-cast film composed of cellulose triacetate (CTA) by adding ferrocene. Owing to the molecular orientation in the film plane of solution-cast films, which results from the normal stress applied during the solvent evaporation process, the average refractive index is usually higher in the plane of the film than in the thickness direction. We found that the addition of ferrocene, which is miscible with CTA, reduced the optical anisotropy by nematic interaction; i.e., ferrocene molecules are forcibly embedded into the film plane accompanying the CTA chains. Because the direction of anisotropic polarizability of ferrocene is perpendicular to the long axis of the molecule, the refractive index in the thickness direction is reduced. Furthermore, the stress-optical coefficient in the glassy state is reduced by the addition of ferrocene.

Summary This work focuses on the effect of different catalytic systems on network structures and thermal properties of the polymer networks from poly(vinyl alcohol) (PVA) and Tung oil. The polymer networks based on Tung oil and PVA using potassium persulfate (KPS) as a thermal catalyst or KPS and sodium thiosulfate as a redox catalyst were performed at 60 °C and 80 °C. FTIR results confirmed that Tung oil could be crosslinked by both catalysts. Moreover, at 60 °C, it can be seen that the crosslinking reaction with the redox catalyst could occur better than with the thermal catalyst. To prove the crosslinking reaction of PVA in the polymer networks, water resistance of the polymer networks was also investigated. It was found that the PVA was successfully crosslinked by thermal catalyst but was not by redox catalyst. Besides, from this result, it could be suggested that, in the redox system, structure of the polymer networks was mainly formed by Tung oil. From DMA results, Tg of PVA with the thermal catalyst is higher than that with the redox catalyst because of the network formation of PVA in thermal catalytic system. While the Tg of Tung oil in the polymer networks with the redox catalyst is higher than that with the thermal catalyst. This is reasonable because the crosslinking reaction of Tung oil with the redox catalyst could easily occur better than with the thermal catalyst. Altogether, crosslink structure of Tung oil exhibited major influence on properties of PVA/Tung oil polymer network.

A methodology for controlling the localization of multi-walled carbon nanotubes (MWCNTs) was studied using an immiscible polymer blend composed of isotactic polypropylene (PP) and ethylene- co -propylene rubber (EPR). We found that the MWCNTs were localized in EPR domains within the composite, which was prepared at 280 °C. EPR molecules bonded to the MWCNT surface are responsible for the localization in EPR. Conversely, MWCNTs preferentially resided in the matrix when the composite was prepared at 190 °C along with nitrogen gas purging. Because of the selective localization of the MWCNTs in the matrix, the composite obtained via mixing at the lower temperature exhibited a higher Young's modulus and yield strength. These findings demonstrate that mixing conditions greatly affect the MWCNT distribution and thus the mechanical properties of PP/EPR blends.

We investigated wavelength dependence of birefringence (Δn) for cellulose acetate propionate (CAP) films stretched at various draw ratios (DRs) and strain rates (SRs), by comparing the result of cellulose triacetate (CTA). CAP exhibited an extraordinary wavelength dispersion of Δn although CTA showed an ordinary dispersion, indicating that Δn of CAP is determined by acetyl and propionyl groups. The extraordinary dispersion for CAP became stronger at larger DR and higher SR. The thermal analysis data suggested that the hot-stretching induces the crystallization of CAP and the crystal size increases with increasing DR and SR. Furthermore, two-dimensional X-ray diffraction pattern of CAP exhibited the orientation of the induced crystal as well as that of CTA, which is one of semi-crystalline polymers. These results mean that the acetyl orientation in CAP becomes stronger than the propionyl orientation. This conclusion is reasonable because acetyl group is more tightly confined to a pyranose ring than propionyl.

We used three-point bending tests to investigate the effects of elastomer lamination on the failure mode of bar-shaped products using isotactic polypropylene (PP). When a thermoplastic elastomer sheet was laminated on PP, which was prepared by double-shot injection molding, the specimen showed high mechanical toughness without signs of stress whitening. Although rubbery materials have low tensile moduli, their bulk moduli are comparable to those of plastics. Therefore, the laminated elastomer, located inside of the bending deformation, prohibits sharp bending angles during the deformation. Consequently, craze formation, which is the origin of stress whitening and leads to brittle fracture, hardly occurs.

Flow-induced segregation and phase-mixing behaviors of polymer blends comprising polycarbonate (PC) and another polymer with low molecular weight, such as poly(methyl methacrylate) (PMMA) and polystyrene (PS), are studied. Although PMMA with low molecular weight is miscible with PC, the PMMA fraction in an injection-molded plate is found to be rich at the surface, suggesting that PMMA is segregated to the surface region under pressure-driven flow in the mold. The high concentration of the PMMA fraction at surface will provide enhanced surface hardness of a product. Furthermore, the PS addition is found to decrease the apparent shear viscosity greatly especially in the high shear rate region at capillary extrusion, which will be responsible for a long spiral flow length at injection-molding. The decrease in the shear viscosity is attributed to the flow-induced phase-mixing, which occurs only in the surface region.

Structure and properties for strands extruded from a capillary rheometer were studied using polyethylene (PE) containing carbon nanotubes (CNTs). We found that the CNT addition surprisingly enhances the chain orientation of PE. The oriented CNTs greatly accelerate the flow-induced crystallization of PE. These findings demonstrate that it will be a new method to enhance the rigidity of PE effectively.Structure and properties for strands extruded from a capillary rheometer were studied using polyethylene (PE) containing carbon nanotubes (CNTs). We found that the CNT addition surprisingly enhances the chain orientation of PE. The oriented CNTs greatly accelerate the flow-induced crystallization of PE. These findings demonstrate that it will be a new method to enhance the rigidity of PE effectively.

The effect of lithium bromide (LiBr) on the structure and properties of poly (vinyl alcohol) (PVA) fibers obtained by wet-spinning was studied. The tensile modulus and strength of a PVA fiber were greatly enhanced irrespective of the post-spinning hot-stretching process. The high degree of molecular orientation arose from the reduction in the crystallinity and hydrogen bonding between PVA chains in the solution resulting from the addition of LiBr, which was revealed by the rheological properties of aqueous solutions. The LiBr was removed from the fiber during the spinning process in the coagulation bath, and during the washing process. This ensures strong hydrogen bonding in the fibers, and results in excellent mechanical properties.

Enhancement of mechanical properties of biodegradable and compostable poly(lactic acid) is remarkably achieved by melt-blending with particular modified natural rubber. The modified natural rubber is prepared by a two-step process using hydrogenation, followed by an epoxidation reaction, in latex phase, which is sustainably derived from the rubber trees. The as-prepared epoxidized hydrogenated natural rubber is used (10% by weight) for the first time, as a toughening agent, in a mixture with poly(lactic acid). The structure modification of the rubber containing hydrogenated and epoxide moieties provides improved compatibility between rubber and poly(lactic acid). The results demonstrate the maximum increment in impact performance and elongation at break of the modified natural rubber/poly(lactic acid) blend with the values of 32.43 kJ/m2 and 348%, respectively. The results reveal that the impact resistance and elongation at break of PLA blend can increase approximately ninefold and forty-ninefold, respectively, compared to the neat PLA. Meanwhile, there is an improvement in tensile strength (41.79 MPa) and modulus (2.02 GPa) of the blend when compared to the unmodified natural rubber/poly(lactic acid) blend (31.39 MPa tensile strength and 1.57 GPa modulus). Furthermore, the microstructure, evidenced by scanning electron microscopy, reveals the presence of the fine rubber particles and the appearance of some fibrils on the impact-fractured surface of the blends. Therefore, the modification of natural rubber improves its compatibility with poly(lactic acid) and enhances the mechanical and impact properties of poly(lactic acid). The successful preparation of natural rubber-based toughening agent using an environmental-friendly latex system paves the way for broadening and diversifying the use of natural rubber and also poly(lactic acid), in which both derived from renewable resources with the truly-sustainable developments and sustainability.

In this paper, we demonstrated that commercially available triblock copolymers such as polystyrene-b-polybutadiene-b-polystyrene (SBS) and polystyrene-b-polyisoprene-b-polystyrene (SIS), used as thermoplastic elastomers, exhibit autonomic self-healing behavior at room temperature without any chemical reaction even after cutting into two separate pieces. The healing efficiency is improved by immediate recombination after cutting, and is attributed to the destruction of the microstructure, i.e.、 polystyrene domains, leading to marked molecular mobility. Furthermore, quenched samples with obscure phase-separation exhibit good healing behavior. Finally, SBS has better healing efficiency than SIS because the solubility parameter of polybutadiene is closer to that of polystyrene than that of polyisoprene; to some extent, the solubility parameter is responsible for enhanced molecular motion owing to the mutual dissolution of both components.

The impact of different mixing methods on flow instability in capillary extrusion was examined using binary mixtures of linear low-density polyethylene with different molecular weights. The polymers were blended using a single-screw extruder, a twin-screw extruder, and a twin-screw mixer. The onset of flow instability changed depending on the mixing method used, even though their linear viscoelastic properties were almost identical. The mixtures that were subjected to mixing methods with weak mixing capability exhibit sharkskin failure even at low shear stress and low values of the maximum draw ratio without rupture in the molten state. The results suggested that mechanically weak points were present, which led to cohesive failure at the strand surface following abrupt stretching at the die exit (i.e., sharkskin failure). In contrast, the mixture that was subjected to thorough mixing exhibited smooth surface at high shear stress and a large maximum draw ratio.

The effect of ion-dipole interaction between lithium cations and oxygen atoms in poly(methyl methacrylate) (PMMA), which leads to the great enhancement of glass transition temperature (Tg), on the linear viscoelastic properties is studied using binary blends of PMMA and lithium trifluoromethanesulfonate (LiCF3SO3). The strong interaction at low temperature leads to the high modulus in the glassy region even near Tg. The interaction becomes weak as increasing the temperature. Consequently, the rheological terminal region is clearly detected without a marked enhancement of steady-state compliance, although the zero-shear viscosity increases by the LiCF3SO3 addition. The result indicates that the crosslinking due to the ion-dipole interaction has a lifetime that decides the longest relaxation time. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2388–2394

Interphase transfer of a coumarone-indene tackifier between natural rubber (NR) and poly(isobutylene) (PIB) was studied. The laminated sheets composed of NR with the tackifier and PIB with the tackifier were annealed at various temperatures to promote the interphase transfer of the tackifier. After separating the post-annealing sheets, the infrared spectra were measured to evaluate the tackifier content in each rubber sheet. It was found that a large amount of the tackifier resided in PIB after annealing at -20 °C, whereas the tackifier moved to NR at 40 °C. Consequently, the NR sheet exhibited lower glass transition temperature T_g after annealing at -20 °C and higher T_g when annealed at 40 °C. The differential scanning calorimetry measurements revealed that the crystallization of NR was responsible for the tackifier transfer. This phenomenon should be noted of interest because the matrix of their blend shows low T_g at low ambient temperature and high T_g at high temperature when NR is the matrix of the blend.

The effect of crystallization on the drawdown force, i.e., the force needed to stretch a molten polymer uniaxially, was studied using conventional polyethylene samples. It was found that the drawdown force of high-density polyethylene (HDPE) increases with increasing the die length. This is attributed to the rapid crystallization owing to the low density of entanglement couplings after passing through a long die. On the contrary, the die length has no/little influence on the drawdown force of linear low-density polyethylene (LLDPE), indicating that the molecular orientation applied in a long die is almost relaxed prior to the crystallization. Even for LLDPE, however, the drawdown force becomes sensitive to the die length by the addition of a small amount of HDPE, because the crystallization process is accelerated.

Poly(ethylene-co-vinyl acetate) with 42 wt% of vinyl acetate shows autonomic self-healing at room temperature without macroscopic flow. Intermolecular diffusion of amorphous chains through the jointed boundary, which occurs because of the large amount of amorphous chains with low glass transition temperature, is responsible for the healing phenomenon. Furthermore, the healing efficiency is found to be enhanced when the separated pieces are recombined immediately after cutting. This result indicates that the cut surface has marked molecular mobility owing to the destruction of crystallites during the cutting process, which is supported by differential scanning calorimetry (DSC) measurements. The marked molecular mobility at the surface is, however, observed only for a short period after cutting, because further crystallization after cutting restricts the molecular motion.

The structure and rheological properties of binary blends of polycarbonate (PC) and polystyrene (PS) were investigated using various PS samples with different molecular weights, namely PS1k (M_w = 1000), PS53k (M_w = 53000), and PS240k (M_w = 240000). The blends with PS53k and PS240k show phase-separated structures, whereas the blend with PS1k is miscible. The shear viscosity decreases greatly on addition of PS53k and PS240k, especially at high shear rates, which would be a great advantage at processing operations. Because the non-linear response occurs in the small strain region for multilayered films of PC and PS240k, the origin of the significant viscosity drop for the phase-separated system is interfacial slippage at the phase boundary.

The effect of post-processing annealing beyond the glass transition temperature on optical transparency was studied using poly(lactic acid) (PLA) films containing a nucleating agent such as N,N′-ethylenebis(stearamide) (EBS) or N,N′-ethylenebis(12-hydroxystearamide) (EBHS). Although the PLA films without the nucleating agent became opaque after exposure to annealing, the film with an appropriate amount of the nucleating agent was found to be transparent (the haze value was lower than 10%). Since the crystallinity was enhanced by annealing, the film showed excellent heat resistance. As compared with EBS, moreover, EBHS had a better capability to produce a transparent film because the aggregates, which appeared during cooling from the molten state, were small. In the case of EBHS, a network structure of fibrous EBHS in molten PLA was confirmed, which was responsible for the reduced size of the PLA crystals and prevented spherulite formation.

The effect of the addition of lithium trifluoromethanesulfonate (LiCF_3SO_3) on the linear viscoelastic properties, crystallization behavior, and mechanical properties of poly(lactic acid) (PLA) was studied. The glass transition temperature (T_g) was enhanced by adding LiCF_3SO_3, without any loss of transparency of the PLA. This was attributed to the ion-dipole interaction between the lithium cation and oxygen atom in the PLA carbonyl group. The interaction weakened at higher temperature. Consequently, the rheological terminal region was clearly detected, which suggested that the system possessed good melt-processability. The Young’s modulus and yield stress at room temperature were also enhanced by the addition of LiCF_3SO_3, although the toughness was reduced due to the brittle failure. Finally, the presence of LiCF_3SO_3 retarded the crystallization of PLA, because the segmental motion of the PLA chains was reduced.

A new technique to show good electroconductivity was proposed using carbon nanotube (CNT) localization in co-continuous immiscible polymer blends comprising ultra-high-molecular-weight polyethylene (UHMWPE) and polycarbonate (PC). When UHMWPE was added to PC/CNT in the molten state in an internal mixer, CNTs started moving to the UHMWPE phase. However, CNTs require a long time to diffuse into the UHMWPE phase owing to a low diffusion constant. Consequently, they remain at the interface between PC and UHMWPE. When the blends have co-continuous structure, the localized CNTs at the phase boundary act as a conductive path, leading to a good electroconductivity. Although a similar morphology is obtained by adjusting the balance of interfacial tensions among polymers and CNT, it is difficult to find a system showing appropriate interfacial tensions. Since the present method is applicable to various polymer blends, it will be an important technique to prepare a conductive nanocomposite.

The effect of a substitution site on orientation birefringence for cellulose triacetate (CTA) was investigated by the addition of xylan ester. Since CTA has three substitution sites (C-2, C-3, and C-6) while xylan ester has two substitution sites (C-2 and C-3), the change of birefringence by xylan acetate (XylAc) is attributed to the contribution of the C-6 acetyl group. Dynamic mechanical analysis and thermal measurements showed a single glass transition peak, indicating that XylAc is miscible with CTA at any compositions. The orientation birefringence (Δn) of CTA/XylAc films stretched beyond the glass transition temperature increased with increasing the XylAc content. The result for the stretched film suggested that the contribution of acetyl group in the C-2 and C-3 sites to Δn is positive while that in the C-6 is negative. The negative sign for the C-6 site is in agreement with the result simulated by using the molecular dynamics method. In addition, Δn of CTA films containing xylan propionate (or butyrate) indicated that the propionyl and butyryl groups in the C-2 and C-3 sites show positive birefringence similar to the acetyl group.

The capillary extrusion property of ethylene–tetrafluoroethylene copolymer (ETFE) is evaluated. It is found that ETFE shows several types of flow instabilities. The shark-skin failure is observed over the first critical shear stress 7.9 × 10 4 Pa. Then, the slip-stick instability is detected at 1.8 × 10 5 Pa, which corresponds to the critical stress of the slippage at the die wall, evaluated by the Mooney method. Moreover, gross wavy melt fracture appears at high out-put rate condition. It is interesting to note that quasi-stable flow region; so-called “super-extrusion”, is observed between slip-stick and wavy melt fracture regions. Because of the steady slippage, ETFE can be extruded at a high out-put rate condition without surface roughness and distortion of extrudates.

A new method to localize poly(methyl methacrylate) (PMMA) at the surface of a miscible blend with polycarbonate (PC) is demonstrated. Low-molecular-weight PMMA, which is found to be miscible with PC, is used in this study. After annealing the PC/PMMA blend in a temperature gradient, PMMA is found to localize on the high-temperature side, as detected by infrared spectroscopy and molecular weight measurements. Furthermore, the sample exhibits good transparency even after annealing. This phenomenon is notable because it is applicable to enhancing the anti-scratch properties of PC.

A contradict interphase transfer of multi-walled carbon nanotubes (MWCNT) is detected in the immiscible polymer pair of polyethylene (PE) and polycarbonate (PC). When laminated sheets composed of PE with MWCNTs and PC are annealed in the molten state of both polymers, MWCNTs are found to move from PE to PC. This transfer phenomenon is originated from the difference in the interfacial tension with the aid of Brownian motion. On the contrary, MWCNTs prefer to reside in the PE phase in the blend of PE, PC and MWCNTs, even when MWCNTs are first dispersed in PC. This result indicates that MWCNTs transfer from PC to PE. The opposite direction of the transfer is attributed to the PE molecules being adsorbed on the surface of MWCNTs, which are generated during mixing.

Phase separation in plasticized cellulose triacetate (CTA) films is investigated to produce a microporous film that can be used in optical devices. Hot-stretched CTA films containing diisodecyl adipate (DIDA) show negative orientation birefringence similar to the hot-stretched pure CTA. After extracting DIDA from the stretched films by immersion into an organic solvent, however, the films exhibit positive birefringence. Moreover, the magnitude of the birefringence increases with the wavelength, known as extraordinary dispersion, which is an essential property in the preparation of an ideal quarter-wave plate. Numerous ellipsoidal pores with micro-scale were detected in the film after the immersion, indicating that DIDA were segregated and formed ellipsoidal domains in the CTA matrix during annealing and stretching. These results indicate that extraordinary wavelength dispersion is given by the combinations of orientation birefringence from CTA and form birefringence from micropores. Furthermore, it was found that annealing time and stretching condition affect the phase separation as well as the shape and size of pores.

The effect of flexible chain on orientation dynamics of a small additive molecule in cellulose acetate propionate (CAP) films is investigated during stretching by means of measurements of birefringence and polarized Fourier-transform infrared (FT-IR) spectrum. The orientation birefringence is enhanced by the additives such as ethylene 2,6-naphthalate (C_2Np) and hexamethylene 2,6-naphthalate (C_6Np) oligomers, suggesting that the additives orient parallel to the CAP chain due to an intermolecular orientation correlation called as the nematic interaction (NI). At a high drawing temperature, the orientation of C_2Np is stronger than that of C_6Np, indicating that the flexible alkyl chain reduces the intermolecular NI with CAP. In contrast, C_6Np orients to the stretching direction rather than C_2Np at a low temperature. The polarized FT-IR spectra show that the orientation of rigid part in C_6Np is delayed from that of the flexible group and matrix CAP chain. Consequently, the contribution of C_6Np to birefringence and its wavelength dependence become stronger with increasing the draw ratio.

Appropriate cooling conditions in melt processing were found to provide crystalline poly(lactic acid) (PLA) with greater mechanical toughness in tensile tests. PLA films cooled near its glass transition temperature Tg showed ductile behavior, whereas those obtained by a quenching process exhibited brittle fracture. The content of gauche-gauche (gg) conformer, which leads to low critical onset stress for shear yielding, increased in the films cooled near Tg. The crystallinity of the films hardly affected their mechanical toughness and proportion of gg conformer except for that with a high degree of crystallinity (>50%). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44960.