The surface orientation of polystyrene measured by liquid contact angle

The surface contact angle of glycerol and of water on polystyrene (PS) films has been found to depend on the extent of uniaxial draw for atactic PS. The contact angle depends on direction for the smooth films of PS drawn by solid state coextrusion. Results as a function of draw ratio to values over 4 on these noncrystalline PS samples, M_w = 6 × 10⁵, have also been interrelated with other measures of orientation such as the anisotropy of surface and bulk properties measured, respectively, by dichroic reflectance infrared spectroscopy and by birefringence.     

Effect of uniaxial drawing of soy protein isolate biopolymer film on structure and mechanical properties

The effect of uniaxial drawing of biodegradable soy protein isolate (SPI) polymer film on mechanical properties was investigated to accelerate the efforts to develop SPI films with improved properties. The films containing 0–30 wt% glycerol were drawn uniaxially up to a draw ratio of 2.5. The mechanical properties of the SPI film increased significantly after uniaxial drawing. The tensile strength of the undrawn film (49.7 MPa) was approximately doubled by subjecting the film to uniaxial drawing to a D.R. of 2.5. Wide‐angle X‐ray diffraction and differential scanning calorimetry measurements did not show evidence of generation of a crystal phase in the drawn SPI films. ATR‐FTIR revealed that the protein film contained mainly α‐helix and β‐sheets secondary structures. Microwave molecular orientation analysis showed that birefringence increased with increasing draw ratios. Mechanical anisotropy of the SPI film via orientation of α‐helix and β‐sheets structure is thought to be responsible for the enhancement of mechanical properties with uniaxial drawing of the SPI films. POLYM. ENG. SCI., 47:374–380, 2007. © 2007 Society of Plastics Engineers.     

Effect of uniaxial drawing on surface chain structure and surface tension of poly(trimethylene terephthalate) film

Changes in the surface chain structure and the critical surface tension of poly(trimethylene terephthalate) (PTT) film under uniaxial drawing were examined by polarized attenuated total reflection infrared (ATR-IR) spectroscopy and contact angle measurement. It was observed from the stress-draw ratio curve and density measurement that the strain-induced crystallization occurs at the draw ratio of 2.5. From the ATR-IR spectra, it was also realized that the surface chain structure changes with the draw ratio, showing a remarkable increase in the surface crystallinity at the draw ratio between two and three. The critical surface tension of uniaxially drawn films increases with the draw ratio due to an increase in the surface crystallinity developed by the strain-induced crystallization. It is concluded that the surface properties of PTT film such as the chain structure at the surface and the critical surface tension are very closely related to the condition of uniaxial drawing.     

Morphological analysis of linear low density polyethylene films by atomic force microscopy

Atomic force microscopy has been used to investigate the morphology of hexene linear low density polyethylene (LLDPE) blown film in the undrawn and drawn states. The morphology of the undrawn film, which is biaxially oriented due to the nature of the extrusion process, is composed of crystallites, which consist of aggregates of lamellae. Elongation of the film caused these crystallites to undergo deformation, resulting in the gradual formation of a fibrillar structure in the draw direction. The transformation of these crystallites into fibrils corresponded with an initial increase in the surface roughness, until 250% elongation. Further extension of the film to 450% caused the surface roughness to reach a plateau. The changes observed in the surface roughness and morphology indicate that drawing of the film caused the crystallites to tilt and slip, rupturing crystalline blocks, which then develop into a fibrillar structure. Further extension of these initial fibrillar structures resulted in a more oriented fibrillar morphology. Wide‐angle x‐ray scattering clearly showed the orientation of the crystals with respect to the draw direction throughout the film. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 777–784, 2002     

Mechanical and thermal anisotropy for uniaxially and biaxially drawn PET

Sheets of two molding grades of polyethylene terephthalate (PET) with weight average molecular weight of 57,000 and 52,000 were drawn uniaxially or biaxially to ratios of up to 3 in a compression mold at 200°C. Tensile modulus measurements were done for axial and transverse strain. Thermal conductivity measurements were done with a transient‐state surface probe for thermal conductivity in the normal‐to‐the surface direction (Kn), as well as the axial (Ka) and transverse (Kt) directions in the plane of the sheet. Values are presented as normalized by the tensile modulus (Mo) or the normal conductivity (Kno), respectively, of undrawn isotropic specimens. For the uniaxial experiments, both M/Mo and Ka/Kno were linearly related to draw ratio. A regression analysis on results for both grades of PET for Ka/Kno in terms of M/Mo gave Y = 0.804*X + 0.286; std. err. of Y est. equal to 0.17. Kn/Kno decreased slightly. This non‐intrusive conductivity measurement provides a convenient means for monitoring the development of increased modulus in hot‐forging processes. Results on biaxially oriented specimens showed lesser modulus increases with draw ratio, consistent with orientation distribution in a plane, rather than in a single direction. Thermal conductivity (Ka/Kno as well as Kt/Kno), however, increased to a greater degree than for the case of uniaxial draw for the higher molecular weight material, suggesting the possibility of tilting of crystalline aggregates in the deformation process.     

Crystal structure and orientation of uniaxially and biaxially oriented PLA and PP nanoclay composite films

Cast films of poly(lactic acid) (PLA) and polypropylene (PP) with 2.5 and 5 wt % organo modified nanoclay were prepared and then uniaxially and biaxially hot drawn at T = 90 and 155°C, respectively, using a biaxial stretcher. The orientation of PLA and PP crystal unit cells, alignment of clay platelets, as well as the extent of intercalation and exfoliation were studied using wide angle X‐ray diffraction (WAXD). The measurement of d‐spacing of the 001 plane (normal to platelets plane) of the clay tactoids indicated the intercalation of the silicate layers for the PLA nanocomposite films, whereas the PP nanofilled films showed only dispersion of the nanoparticles (i.e., neither intercalation nor exfoliation were observed). The intercalation level of the clay platelets in PLA was almost identical for the uniaxially and biaxially drawn films. Our finding showed that the crystallite unit cell alignments are appreciably dependent on uniaxial and biaxial stretching. Moreover, the incorporation of clay to some extent influenced the orientation of the crystal unit cell axes (a, b, and c) of the oriented films. The silicate layers revealed a much higher orientation into the flow direction in the uniaxially stretched films compared to the biaxially drawn samples. In addition, the orientation of the 001 plane of nanoclays was significantly greater in the PLA compared to the PP nanoclay composite films probably due to a better intercalation and stress transfer in the former. Morphological pictograms illustrating the effects of uniaxial and biaxial stretching on the clay orientation are proposed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Fabrication of hydrophobic Ti3SiC2 surface with micro-grooved structures by wire electrical discharge machining

The near-superhydrophobic Ti₃SiC₂ surfaces with regular and controllable micro-grooved structures were fabricated by wire electrical discharge machining (WEDM). The surface topographies and chemical compositions of smooth and micro-grooved Ti₃SiC₂ surfaces were characterized. The micro removal mechanism of Ti₃SiC₂ in the process of electrical discharge machining was also analyzed. The wetting mechanism of micro-grooved Ti₃SiC₂ surface was discussed along with the static contact angle, anisotropic wettability and contact angle evolution versus time. The relationships between parallel and perpendicular contact angles, depth-width ratio of micro-grooved structures and surface roughness of textured surface were investigated. The experimental results show that the parallel contact angle on the textured Ti₃SiC₂ surface increased by about 164% compared with the one on the smooth surface, and near-superhydrophobic surface with obvious anisotropy was roughly achieved. The experimental parallel contact angles were very close to theoretical contact angles calculated by Cassie-Baxter formula. It is confirmed that the depth-width ratio may be used to predict the parallel contact angle with the average prediction error of 2.4%. The perpendicular contact angles had a good correlation with the depth-width ratio and surface roughness.     

Highly crystalline and oriented high‐strength poly(ethylene terephthalate) fibers by using low molecular weight polymer

High‐strength poly(ethylene terephthalate) (PET) fibers were obtained using low molecular weight (LMW) polymervia horizontal isothermal bath (hIB), followed by postdrawing process. We investigated the unique formations of different precursors, which differentiated in its molecular orientation and crystalline structures from traditional high‐speed spinning PET fibers. Sharp increase in crystallinity was observed after drawing process even though the fibers showed almost no any crystallinity before the drawing. Properties of as‐spun and drawn hIB and control filaments at different process conditions were compared. As would be expected, performances of resulted treated undrawn and drawn fibers have dramatically improved with developing unique morphologies. Tenacities more than 8 g/d for as‐spun and 10 g/d for drawn treated fibers after just drawn at 1.279 draw ratio were observed. These performances are considerably higher than that of control fibers. An explanation of structural development of high‐strength fibers using LMW polymer spun with hIB is proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42747.     

Molecular orientation of extruded PET/LCP blend films. Part I: Polarized infrared spectroscopy

The polarized infrared (IR) spectroscopy technique was used to evaluate the surface uniaxial molecular orientation of films of poly(ethylene terephthalate) (PET), two thermotropic liquid crystalline polymers (LCPs), Vectra®A950 and Rodrun®LC5000, and their blends obtained by extrusion. The molecular orientation of the LCP and of the crystalline and amorphous PET phases in the draw direction was evaluated along the transverse section of the films and as a function of the blend composition. A compatibilizer agent was used to improve the interfacial adhesion between the PET and LCPs. The results showed that the surface molecular orientation of both LCPs was very high along the draw direction. However, when blended, the orientation of the LCP phase decreased drastically, it was dependent of its content and varied along the transverse section of the extruded films. The maximum orientation was observed in the blend with 5 wt % LCP content and at the position where the shear rate was maxima. The LCP Vectra®A950 showed higher orientation than the Rodrun®LC5000, as a pure material and as blended. For the PET phases, an alignment of the amorphous phase in the draw direction due to the presence of LCP and compatibilizer agent was observed. The crystalline phase of PET, however, showed no significant orientation in the draw direction. The compatibilizer agent proved efficient for both PET/LCP systems. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2241–2248, 2006     

傅里叶变换显微红外光谱技术在涤纶中的应用

利用傅里叶变换红外光谱仪和红外显微镜测定了涤纶(PET)的未完全拉伸丝(UDY)、预取向丝(POY)、完全拉伸丝(FDY)的红外光谱,测定了3种纤维的取向度、结晶度。结果表明:傅里叶变换显微红外光谱技术可以方便的测定PET单纤维的红外光谱,且从峰的偏移可以判断结晶带的变化;PET纤维随着拉伸倍数的提高,其取向度和结晶度都相应提高。     

Strain‐induced crystallization in uniaxially drawn PETG plates

The copolyester poly(ethylene glycol‐co‐cyclohexane‐1,4‐dimethanol terephthalate) (PETG) is used industrially as an uncrystallizable polymer, whereas PET is an inherently crystallizable polymer. Nevertheless, a crystalline phase could appear in the material. To create a strain‐induced crystalline phase in an initially amorphous PETG material, plates were placed in the heating chamber of a tensile machine at 100°C and uniaxially drawn to obtain different samples with various draw ratios. During DSC analysis of highly drawn samples, perturbations of the baseline appear above the glass‐transition temperature, consisting of weak exothermic and endothermic phenomena. Comparison of DSC and X‐ray diffraction analysis of drawn PETG and PET shows that a strain‐induced crystalline phase appears in this copolyester. A spherulitic superstructure could also appear after lengthy annealing. Analysis of this semicrystalline material allowed estimation of the degree of crystallinity, about 3% after a drawing at high draw ratio and about 11% for undrawn annealed material. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3405–3412, 2001     

Ultrasonic velocity and attenuation of polymeric solids under oscillatory deformation. III: Drawn films of high density and linear low density polyethylene and their blends

Viscoelastic nonlinearity was examined on uniaxially drawn films of high density and linear low density polyethylenes and their blends using dynamic ultrasonic measurements. It was found that nonlinearity due to plastic deformations, such as slippage and dislocations, occurs in the fibrous structures. Plastic deformations were different from those in corresponding undrawn films. For undrawn films, the formation and/or deformation of crystal defects and voids were caused by the disruption of spherulitic structures. Nonlinearity was smaller for drawn films than for undrawn films, suggesting that the superstructure of drawn films is more uniform and more stable for mechanical deformations.     

Drawing in high pressure CO2—a new route to high performance fibers in memory of late Roger Porter

In this paper, we introduce a new draw technique for polymer orientation and apply it to different polymer fibers: poly(ethylene terephthalate) or PET, nylon 6,6, and ultra‐high molecular polyethylene (UHMWPE). In this technique, a polymer is drawn uniaxially in supercritical CO₂ using a custom high‐pressure apparatus. This technique can be used in replacement of a traditional drawing process or as a post‐treatment process. With PET, the technique is not effective at temperatures at or below 130°. In contrast, the process is highly effective for nylon 6,6 where CO₂ drawn fibers show significantly higher crystallinity and orientation along with improved mechanical properties. While the fibers are plasticized, the drawability of the fibers is only slightly dependent on temperature. High pressure CO₂ drawing of ultrahigh molecular weight polyethylene (UHMWPE) fibers is equally effective. Commercial high performance fibers can be drawn up to a ratio of 1.9 in asecond stage, resulting in large increases in tensile modulus and small improvements in tensile strength.     

Surface morphology and crystalline orientation of uniaxially drawn polytetrafluoroethylene films

For polytetrafluoroethylene (PTFE) films drawn uniaxially at 100, 150, 250, and 350°C, the morphology and degree of crystalline orientation were investigated by electron scanning microscopy and wide-angle X-ray diffraction, respectively. On the surface of the PTFE films which were heat-treated at 350°C for 2 h before the drawing, granules with a diameter of about 2 μm and bands with a width of about 0.3 μm were observed. By the drawing below the melting point, the bands are transformed into fibrils and a porous structure is formed by the drawing above the draw ratio (λ) of about 1.3. By drawing above the melting point, striations appear perpendicularly to the draw direction, and the collapse of the granules is observed. The orientation of the crystallites increases rapidly with increasing the draw ratio and approaches a plateau at λ ≈ 1.5 for the films drawn above the melting point and at λ ≈ 2.0 for that below it.     

Characterization of uniaxially drawn poly(4-methyl-pentene-1)

For poly(4-methyl-pentene-1) (PMP41) of increasing uniaxial draw, X-ray diffraction analysis reveals a shift of diffraction peaks at lower 2θ angle and the concurrent generation of new peaks at higher angles. The corresponding crystal structure at lower draw ratio is a common tetragonal form and that at higher draw is orthorhombic. The heat of fusion of the perfect tetragonal crystal of undrawn PMP41, obtained by X-ray diffraction and d.s.c., is 4.4kJ mol⁻¹. The crystallinity of drawn PMP41 increases with draw, up to ∼90% for a draw ratio > 30. The fraction of extended chains for a draw ratio of 10, calculated from the linear thermal expansion coefficient, is 26%. The modulus of drawn PMP41 is proportional to the fraction of extended chains.     

Studies of the morphology of one-way drawn poly(ethylene terephthalate) films by X-ray diffraction

Films made by stretching amorphous poly(ethylene terephthalate) (PET) in one direction have been examined using techniques of wide- and narrow-angle X-ray diffraction. The films were not subsequently annealed. The in-plane c-axis orientation of crystallites was assessed from measurements of reflections from 1&;#x0304;05 crystal planes as in the method of Dumbleton and Bowles. However, we found that rather than tending to align parallel to the draw direction, the crystallites tended to lie in two groups inclined at a small angle to the draw direction. The angle of tilt of this ‘preferred’ direction to the draw axis became smaller for more highly drawn films, and a plot of tensile strength against tilt angle shows a trend to a ‘strength limit’ for zero tilt. (This tilt must not be confused with the well-known and quite different crystalline tilt which occurs after drawn PET is annealed.) Wide-angle diffraction has also been used to estimate crystal dimensions, and low-angle diffraction was used to determine long-period spacings. An analysis of the shape of the diffraction maxima gave an estimate of the shape of the diffracting units, and their influence on mechanical properties is discussed.     

Lewis acid-base complexation of polyamide 66 to control hydrogen bonding, extensibility and crystallinity

Polyamide 66 (PA66) has been complexed with the Lewis acid GaCl₃ for the purpose of disrupting the interchain hydrogen bonded network. FTIR and ¹³C-NMR observations indicate that Ga metal cations form a 1:1 complex with the carbonyl oxygens of the PA66 amide groups. PA66-GaCl₃ films are amorphous and rubbery with a single relaxation, attributable to the glass transition temperature, at ∼−32 °C and a structure that appears by X-ray diffraction to be thermally stable to at least 200 °C. The complexed films could be drawn at room temperature to draw ratios (DR) up to ∼30, and could then be decomplexed, or regenerated, by soaking in water. GaCl₃ complexation and subsequent regeneration of PA66 was accomplished without changing its molecular weight, and all but ∼5 mol% of the amide groups in the regenerated PA66 were uncomplexed. The undrawn regenerated films regain levels of crystallinity much lower than possessed by the uncomplexed PA66 reference film. However, up to a DR of 8, drawing prior to regeneration increases the crystallinity, reaching crystallinity levels that are high for PA66, that has not been heat treated, and that are almost twice higher than in the uncomplexed (undrawn) reference film. It is intriguing that, in this DR regime, crystallinity increases quite sharply as the film is extended, despite the fact that molecular orientation does not appear to be increasing. For DR>8, the crystallinity decreases, but remains above that of the reference film. The level of crystallinity in PA66 can be controlled over a much wider range by the complexation-drawing-regeneration process than by conventional drawing processes.     

Molecular structures and physical properties of heat‐drawn conjugate fibers

As‐spun poly(trimethylene terephthalate) (PTT)/poly(ethylene terephthalate) (PET) side‐by‐side conjugate fibers were drawn to investigate the effects of drawing conditions on structure development and physical properties. Effects of draw ratio and heat‐set temperature were observed. In the state of an as‐spun fiber, the molecular orientation of PTT was higher than PET, whereas PET molecular orientation increased remarkably over PTT with increasing draw ratio. Crimp contraction increased sharply at a draw ratio over 2.0, where the crystalline structure of the PET developed sufficiently. A heat‐set temperature of at least 140°C was required to develop sufficient crimp contraction. The crystallinity and orientation of the PET were attributed mainly to the crimp contraction of the drawn fiber. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Structure and properties of MDO stretched polypropylene

Two polypropylene cast films of different crystalline structures (one with coexisting small rows of lamellae and spherulites and the other with only a spherulitic structure) were prepared by extrusion. The produced cast films were uniaxially hot drawn at T = 120 °C using a machine direction orientation (MDO) unit and the changes in structure and morphology were examined and related to barrier as well as tear and puncture properties. Structural changes in terms of the degree of crystallinity and crystal size distribution, orientation of the amorphous and crystalline phases, and the deformation behavior at the crystal lattice and lamellae scales were investigated using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), wide angle X-ray diffraction (WAXD), and small angle X-ray scattering (SAXS), respectively. A significant effect of the original crystal morphology on the alignment of the amorphous and crystalline phases was observed from FTIR and WAXD. The results also revealed that the deformation behavior of the crystal structure was dependent on the draw ratio (DR). Our findings showed that by increasing DR the crystal lamellae first broke up and oriented along the drawing direction and then, at large DR, they were deformed and created a fibrillar structure. Morphological pictograms illustrating the effects of original morphology and draw ratio on the stretched film microstructure are proposed. The tear resistance along the machine direction (MD) decreased significantly with increasing DR whereas the puncture resistance increased drastically. Finally, the oxygen transmission rate (OTR) of the MDO stretched films could be correlated with the orientation parameters as well as the β-relaxation peak magnitude of the amorphous tie chains.     

Contact Angle of Ethanol and n‐Propanol Aqueous Solutions on Metal Surfaces

The contact angles of the aqueous solution of ethanol and that of n‐propanol on copper, aluminum, and stainless steel surfaces are reported. The contact angles were measured under atmospheric conditions, and then under vapor‐liquid equilibrium conditions at 1 atm and different temperatures. The results showed the variations of the contact angles with the concentrations of aqueous solutions on different metal material surfaces with different roughness. Some unstable behavior of the wetting ability around the azeotropic point of a binary solution is reported. Influences of concentration, kind of materials, and the surface roughness on the wetting ability are discussed. The model for predicting the contact angle of alcohol aqueous solutions on metal surfaces under atmospheric and vapor‐liquid two‐phase equilibrium conditions at 1 atm is derived from the Young equation.