Imbedded Fiber Retraction Research Articles

A multiple approach in determination of interfacial tension of biodegradable melt-mixed PBAT/EVOH blends: Correlation of morphology, rheology and mechanical properties

The interfacial tension of biodegradable melt-mixed blends of poly(butylene adipate-co-terephthalate), PBAT, and poly(ethylene-co-vinyl alcohol), (EVOH), was measured by breaking thread (BT), imbedded fiber retraction (IFR), and rheological methods. The PBAT-rich blends were prepared under different melt mixing conditions in order to investigate the effect of mixing conditions and possibility of reactive mixing between the blend components on the blend morphology, rheology, mechanical properties and interfacial tension values. The conditions were varied based on a Taguchi design of experiment using four factors namely EVOH content (0–30 wt%), mixing time (2–15 min), rotor speed (50–90 rpm), and mixing temperature (185–200 °C), each varying at three levels. The average size of EVOH droplets in PBAT matrix was determined for each blend by a field emission-scanning electron microscopy technique. The values of interfacial tension of PBAT/EVOH were found to be 2.57 ± 0.22 and 2.73 ± 0.30 mN m−1 by the BT and IFR methods, respectively. The Palierne, Gramespacher, and Bousmina models were fitted to the rheological data to verify the interfacial tension of the blends. The continuous relaxation spectrum of the blends was determined in order to obtain the relaxation time of the EVOH droplets in the PBAT matrix. The Taguchi analysis revealed that the most effective factor is the EVOH content, and other factors do not play a significant role in the ultimate properties of the blends. Finally, based on the obtained mechanical properties, the possibility of reactive mixing under the applied mixing conditions was ruled out by means of repeated differential scanning calorimetry (DSC) and rheological measurements.

Comparative measurement of interfacial tension by transient dynamic methods

AbstractAn experimental comparison between different techniques for the interfacial tension measurement is presented for polyamide‐6 and polystyrene pair. The techniques are transient dynamic methods, which include the breaking thread (BT) method, the imbedded fiber retraction (IFR) method, the deformed drop retraction (DDR) method, and two modified DDR methods. The modified DDR methods combine the analytical power of the DDR method with experimental simplicity of the BT and IFR methods, respectively. Interfacial tension values obtained by the modified DDR method that combines the BT method is much lower than those by the other methods. Among all techniques, the modified DDR that combines the IFR method is found to be most convenient and accurate method. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99:1910–1918, 2006

Interfacial Tension Errors from the Cohen and Carriere Analysis of Imbedded Fiber Retraction

Immiscible polymers are often blended together to create new materials with desired properties. Knowledge of the interfacial tension between the immiscible polymers is important when designing such blending processes. Traditional methods of measuring the interfacial tension between low molecular weight fluids, e.g., the pendant or sessile drop method, the Wilhelmy balance, and the spinning drop method, do not work well for molten polymers because their high viscosity requires unacceptably long times for equilibration. Therefore, “dynamic” methods, which use the kinetics of interfacial tension-driven motion to obtain the interfacial tension, have been devised for polymers.1-6 One such method, the imbedded fiber retraction method, is the subject of this paper. The purpose is to demonstrate that the Cohen and Carriere (CC) model1,2 that is commonly used to analyze fiber retraction experiments can cause large errors in interfacial tension, whereas an alternate analysis by Tjahjadi, Ottino, and Stone (TOS)7 gives reliable interfacial tension values. A notable feature of our experimental approach is that the fiber retraction experiments are benchmarked rigorously: we are able to measure the equilibrium interfacial tension in the same experiment as the fiber retraction.

Evaluation of imbedded fiber retraction phenomenological models for determining interfacial tension between molten polymers

In this work, the interfacial tension for several polymer pairs, namely polypropylene/polystyrene (PP/PS), PP/polycarbonate (PC), PP/polyamide 6 (PA-6) and low density polyethylene (LDPE) and ethylene vinyl alcohol copolymer (EVOH) was evaluated as a function of temperature using the imbedded fiber retraction method (IFR). Two phenomenological models were used and compared to infer the interfacial tension from the evolution of the imbedded fiber back into a sphere: [Carriere CJ, Cohen A, Arends CB. J Rheol 1989;33:681–9. [1] and Tjahjadi M, Ottino JM, Stone HA. AIChE J 1994;40:385–94. [2]]. It was shown that Carriere et al.'s model overestimates the value of interfacial tension whereas Tjahjadi et al.'s model leads to results that corroborate the ones obtained using other experimental methods. A method to further increase the accuracy of Tjahjadi et al.'s model was proposed. Using this method the interfacial tension for the different polymer pairs studied was evaluated and shown to decrease linearly with increasing temperature.

CFD evaluation of drop retraction methods for the measurement of interfacial tension of surfactant-laden drops

Drop retraction methods are popular means of measuring the interfacial tension between immiscible polymers. Experiments show that two different drop retraction methods, imbedded fiber retraction (IFR) and deformed drop retraction (DDR), give inconsistent results when a surfactant is present on the surface of the drop. These inconsistencies are deemed to be due to dilution of the surfactant and due to gradients in interfacial concentration of surfactant along the drop surface. This physical picture is quantified for the simple case of a Newtonian drop in a Newtonian matrix, with an insoluble, nondiffusive surfactant at the interface. The drop is deformed in computational fluid dynamics simulations by shearing the matrix, and then allowed to retract. Dilution and interfacial tension gradients effects are found to be especially large at the early stages of retraction, making IFR unsuitable for measuring the interfacial tension of surfactant-laden interfaces. The effects of surfactant dilution and gradients are found to persist even at late stages of retraction, causing the DDR method to underestimate the equilibrium interfacial tension significantly. The largest underestimates occur when the drop viscosity is lower than the matrix viscosity.

Surface energy parameters of polymers from directly measured interfacial tension with probe polymers

The surface energy parameters of polycaprolactone (PCL) were determined at 160 and 180°C from its interfacial tensions with probe polymers. The probe polymers were polystyrene (PS) and poly(methyl methacrylate) (PMMA). This method is based on the well-known relationship between blend interfacial tension and polymer surface energy parameters, and requires the use of at least two probe polymers, whose surface energy parameters at the temperature of interest have been independently determined. It also requires direct measurement of blend interfacial tension at the high temperatures of interest. The interfacial tensions were obtained from direct measurements by the imbedded fiber retraction method. The following results were obtained: (a) γ P (polar component) values for PCL was within the range reported using other methods, (b) γ D (dispersion component) values for PCL decreased with increasing temperature, consistent with expectations and (c) γ D values for PCL were on the high end, but still within the rather broad range of reported values.

Changes in the interfacial properties of PC/SAN blends with compatibilizer

AbstractBlock copolymers of polycarbonate‐b‐poly(methyl methacrylate) (PC‐b‐PMMA) and tetramethyl poly(carbonate)‐b‐poly(methyl methacrylate) (TMPC‐b‐PMMA) were examined as compatibilizers for blends of polycarbonate (PC) with styrene‐co‐acrylonitrile (SAN) copolymer. To explore the effects of block copolymers on the compatibility of PC/SAN blends, the average diameter of the dispersed particles in the blend was measured with an image analyzer, and the interfacial properties of the blends were analyzed with an imbedded fiber retraction (IFR) technique and an asymmetric double cantilever beam fracture test. The average diameter of dispersed particles and interfacial tension of the PC/SAN blends were reduced by adding compatibilizer to the PC/SAN blends. Fracture toughness of the blends was also improved by enhancing interfacial adhesion with compatibilizer. TMPC‐b‐PMMA copolymer was more effective than PC‐b‐PMMA copolymer as a compatibilizer for the PC/SAN blends. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2649–2656, 2003

Comparison between five experimental methods to evaluate interfacial tension between molten polymers

AbstractIn this work, an experimental comparison between five different techniques to measure interfacial tension between molten polymers is presented. The five techniques include two equilibrium methods: the pendant drop (PD) and the sessile drop (SD); two dynamic methods: the breaking thread (BT) and imbedded fiber retraction (IF); and a rheological method based on linear viscoelastic measurements of the blend (RM). The polymer pairs studied were polystyrene/polypropylene (PS/PP); and PP/high density polyethylene (PP/HDPE). It was possible to determine the interfacial tension between PP/PS with all the methods tested and the results corroborated within 20%. However, the interfacial tension between PP and HDPE could be evaluated only using rheological methods because of a too‐small difference of index of refraction between both polymers. The experimental precision increased in the following order: RM < SD < BT < IF < PD. The rheological method had the advantage of being simpler and faster than dynamic and equilibrium methods. However, when using the rheological method, care should be taken because the results obtained may depend upon the concentration of the blend used for the measurements. It was observed that the pendant drop and breaking thread methods cannot be used for polymers with high viscosity (above 5 × 105 Pa.s).

Interfacial tension of poly(lactic acid)/polystyrene blends

AbstractPoly(lactic acid) (PLA) is a biodegradable synthetic polyester with unique properties that make it an excellent candidate for biomaterial blends. It provides improved moisture resistance to blends with biopolymers and biodegradability/biocompatibility to blends with synthetic polymers, without impairing the useful properties of blend components. The successful development of materials from blends of PLA requires an understanding of the factors affecting the interfacial properties of such blends. In this work, the effect of temperature on the interfacial tension of PLA/polystyrene (PS) blends was measured at 170–200 °C with the imbedded fiber retraction (IFR) method. IFR allows for the direct measurement of the interfacial tension of blends with high molecular weight/high viscosity components. In the temperature range studied, the interfacial tension of PLA/PS was independent of temperature and had a value of 5.4 ± 1.3 dyn/cm. The interfacial tension was also calculated from the surface energies of PLA and PS with geometric mean (GM), harmonic mean (HM), and Antonoff's equations and from solubility parameters with the procedure of Luciani et al. IFR measured values were similar to those predicted by the procedure of Luciani et al. and Antonoff's equations, which gave 4.4 and 3.0 ± 1.4 dyn/cm, respectively. The GM and HM methods predicted much lower values of 1.1 ± 0.5 and 1.7 ± 1.1 dyn/cm, respectively. Published 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2248–2258, 2002

Effect of temperature and molecular weight on the interfacial tension of PS/PDMS blends

The imbedded-fiber retraction (IFR) method was used to study the effect of temperature and PDMS molecular weight on the interfacial tension of PS/PDMS blends. The interfacial tension decreased with increasing temperature and analysis of the temperature dependence using a simple linear fit gave –dγ/dT value of 0.058±0.010 dyn/cm-deg. Reported –dγ/dT values of PS/PDMS blends are highly dependent on the molecular weights of the polymers and can have values that are 0. Our interfacial tension values were independent of the molecular weight of PDMS and this was attributed to the molecular weights studied here being well above the entanglement values of both polymers. However, analysis of interfacial tension data from this work and the literature showed the following empirical relationship between apparent blend molecular weight, Mb, and interfacial tension of PS/PDMS blends with a correlation of 0.94: γ12=γ0+k2Mb (–2/3), where γ0=7.3±0.3 dyn/cm; k2=–517±41 (dyn/cm)(g/mol)2/3.

Interfacial tension measurement between immiscible polymers: improved deformed drop retraction method

This paper describes an improvement of the technique to measure interfacial tension in immiscible polymer blends. Our method is based on the droplet retraction method, in which one relates the kinetics of relaxation of a deformed droplet to the interfacial tension between the matrix and droplet. Previously, the problem with this technique has been the difficulty in preparing axisymmetric ellipsoidal droplets. In our work, we demonstrate that perfect axisymmetric ellipsoidal droplets are produced at a later stage of relaxation of short imbedded fibers. With this technique, we utilize the strengths of both the deformed droplet method and the imbedded fiber retraction method while overcoming their shortcomings. The interfacial tension value thus obtained was compared to that by conventional methods. Additionally, the effect of confinement by external walls on the interfacial tension measurement was studied. Confinement affects interfacial tension measurement when the gap between the walls is less than two times the equilibrium drop size.

Interfacial tension of polycaprolactone/polystyrene blends by the imbedded fiber retraction method

AbstractPolycaprolactone (PCL) is a biodegradable polyester that is widely used in blends with synthetic and natural polymers for various applications. PCL is blended with biopolymers such as starch to improve its wet mechanical properties without impairing the biodegradability and other useful properties of starch. In spite of its importance, little is known about the interfacial tension of PCL blends. Indirect estimates of the room‐temperature interfacial tension of PCL blends using wettability methods have been reported. However, direct measurements of the interfacial tension of PCL blends have not been achieved until now, mainly because of the unsuitability of existing equilibrium methods for measuring the interfacial tension of high viscosity blends. We have measured the interfacial tension of PCL/PS blends using the imbedded fiber retraction (IFR) method. The IFR is a dynamic method that allows for the measurement of interfacial tension of high viscosity polymer blends in a relatively short period of time. The interfacial tension of PCL/PS blends was measured from 160 to 200°C. In this temperature range, the interfacial tension of PCL/PS blends is independent of temperature and has a value of 7.6 ± 1.8 dyn/cm. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3145–3151, 2002; DOI 10.1002/app.10178

The effects of PC‐PMMA block copolymer on the compatibility and interfacial properties of PC/SAN blends

AbstractBlock copolymers of polycarbonate (PC) and polymethylmethacrylate (PMMA), PCb‐PMMA, were examined as compatibilizers for blends of PC with styrene‐co‐acrylonitrile (SAN) copolymer. PC‐b‐PMMA was added to blends of PC with SAN containing various amounts of AN. The average diameter of the dispersed particles was measured with an image analyzer, and the interfacial properties of the blends were analyzed with an imbedded fiber retraction (IFR) test and an asymmetric double cantilever beam fracture test. The average particle size and interfacial tension of the PC/SAN blends reached a minimum value when the SAN copolymer contained about 24 wt% AN. A maximum in the adhesion energy was also observed at the same AN content. Interfacial tension and particle size were further reduced by adding PC‐b‐PMMA to the PC/SAN blends. Fracture toughness of the blends was also improved by enhancing the interfacial adhesion by the addition of PC‐b‐PMMA. The addition of PC‐b‐PMMA copolymer was more effective at improving the interfacial properties of PC/SAN blends than was varying the AN content of the SAN copolymers. The interfacial properties of the PC/SAN blends were optimized by adding a block copolymer and using an SAN copolymer that had minimum interaction energy with PC.

Temperature dependence of the interfacial tension of PS/PMMA, PS/PE, and PMMA/PE blends

The effect of temperature on the interfacial tension for PS/PMMA, PS/PE, and PMMA/PE was measured using the imbedded fiber retraction method. Interfacial tensions for PS/PMMA, PS/PE, and PMMA/PE were measured over temperature ranges of 160–250 °C, 140–220 °C, and 140–220 °C, respectively. The interfacial tension was found to follow a dependence of 3.6–0.013 T dyn/cm, 7.6–0.051 T dyn/cm and 11.8–0.017 T dyn/cm for PS/PMMA, PS/PE, and PMMA/PE, respectively. Comparison of the data with the mean field theory of Helfand and Sapse were made; however, a simple linear fit to the data described the temperature dependence in the experimental window as well as the predictions of the mean field theory.

Critical Experimental Comparison between Five Techniques for the Determination of Interfacial Tension in Polymer Blends: Model System of Polystyrene/Polyamide-6

A critical review and experimental comparison between different techniques for the determination of interfacial tension are presented for a model polymer pair. Five experimental methods were applied to measure the interfacial tension for the model pair of polystyrene (PS) and polyamide-6 (PA-6) at the same temperature. The techniques include three dynamic methods (the breaking thread method, the imbedded fiber retraction method, and the retraction of deformed drop method), one equilibrium method (the pendant drop method), and a rheological method based on linear viscoelastic measurements. The advantages, the limitations, and the difficulties of each technique are discussed and compared.

Measurement of Interfacial Tension between Polymer Liquids : Pendant Drop, Improved Imbedded Fiber Retraction and Steady Shear Flow Methods

The interfacial tension between a poly (isobutylene) (PIB) and a poly (dimethylsiloxane) (PDMS) was obtained by an improved imbedded fiber retraction method from the observation of the PDMS (or PIB) droplet shape in the PIB (or PDMS) matrix after application of the step shear strain. The interfacial tension was also obtained from the observation of the PDMS (or PIB) droplet shape during the steady shear flow. We compared the values of interfacial tension obtained by these methods with the value determined by the pendant drop method. It was found that these values agree fairly well when the viscosity ratio of the droplet to the matrix is around unity.

Modification of the polycarbonate/poly(vinylidene fluoride) interface by poly(methyl methacrylate). Effect on the interfacial adhesion and interfacial tension

AbstractPolycarbonate (PC) and poly(vinylidene fluoride) (PVDF) are two immiscible polymers which form two‐phase blends with weak interfacial adhesion and high interfacial tension. This situation may be changed by the addition of poly(methyl methacrylate) (PMMA), which concentrates preferably in the PVDF‐rich phase, but also at the PVDF/PC interface. The interfacial activity of PMMA was estimated by the measurement of the interfacial adhesion and interfacial tension in relation to the PMMA content in the PVDF/PC blends. The interfacial adhesion between PC and homogeneous PVDF/PMMA blends of various compositions was measured by the dual cantilever beam technique. The imbedded fiber retraction method was used for the measurement of the interfacial tension. A very beneficial effect was observed when PVDF was premixed with PMMA amounts increasing up to ca. 35 wt.‐%. Beyond that content, the improvement tends to level off.

Measurement of Interfacial Tension between Polymer Melts : Improved Imbedded Fiber Retraction, Breaking Thread and Dynamic Viscoelasticity Methods

We improved the imbedded fiber retraction (IFR) method as a simple method to obtain the interfacial tension between polymer melts. A force balance equation for a fiber in an immiscible matrix by Cohen and Carriere is solved for a more realistic fiber shape at later stage of retraction. Moreover, unknown hydrodynamic coefficient in the balance equation is determined theoretically as 0.125. The interfacial tension between polystyrene (PS) and poly (methy methacrylate) (PMMA) is measured by the improved IFR (IIFR) method as well as the breaking thread method and dynamic viscoelasticity method. In dynamic viscoelasticity method, we determine the interfacial tension by fitting the Palierne theory with dynamic viscoelastic data. The interfacial tension obtained from the three methods agrees fairly well and is found to be about 1.6 mNm-1 at 180°C and 1.4mNm-1 at 200°C.

The effects of short-chain branching and comonomer type on the interfacial tension of polypropylene-polyolefin elastomer blends

The imbedded fiber retraction method was used to assess the effect of increasing octene content and comonomer type on the compatibility of polypropylene-polyolefin elastomer (PP-POE) blends via direct measure of the interfacial tension. The interfacial tension was found to decrease monotonically with increasing octene content from a starting value of 1.5 ± 0.16 dyn cm at an initial octene level of 9% down to 0.56 ± 0.07 dyn cm at an octene content of 24%. These effects can be interpreted in terms of the effective decrease in the molecular weight between chain ends for the branched POE materials. The experimental data were found to be described well by a modification of the empirical relationship used to describe the effect of molecular weight on the interfacial tension for linear materials. The power-law parameter was found to be numerically equivalent for that obtained for the molecular weight dependence of linear materials. The measured interfacial tension was also found to be dependent on the type of comonomer used in the PP-POE systems. The interfacial tension ranged from 1.07 ± 0.09 dyn cm for a PP-POE system made using ethylene-propylene down to 0.56 ± 0.07 dyn cm for a PP-POE made using ethylene-octene (24% octene). © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1175–1181, 1997

The effect of temperature on the interfacial tension of polycarbonate/polyethylene blends

AbstractControlling interfacial tension during the processing of blends is critical to developing morphologies that will yield consistent and acceptable mechanical properties. Determination of the interfacial tension is important in developing a predictive understanding of the effects of processing conditions on the morphology and the physical properties of multicomponent systems. The focus of the research reported herein was to investigate the temperature dependence of the interfacial tension for blends composed of polycarbonate (PC) and polyethylene (PE). The effects of temperature were characterized by direct measurements of the interfacial tension using the imbedded fiber retraction (IFR) method. The interfacial tensions of PC/PE were measured at 210, 220, 230, and 240°C. The temperature dependence of the interfacial tension was found to be −0.018 ± 0.006 dyn/cm‐°C. In general, the interfacial tension, evaluated for low‐viscosity simple fluids, is commonly a weak function of temperature (on the order of 0.01 dyn/cm‐°C). The results found in this study are in accord with those findings.