The Breaking Thread Method

Elemans PHM, Janssen JMH and Meijer HEH (1990) The breaking thread method the measurement of interfacial tension in polymer systems. J Rheol 34 1311-22. 

Minkova, L., Yordanov, H., Filippi, S., and Grizzuti, N. 2003. Interfacial tension of compatibilized blends of LDPE and PA6 The breaking thread method. Polymer 44 7925-7932. 

Table 1.1 Interfadal tension (k) between polymer melts based upon the breaking thread method (Yoon and White [146]).

The variety of experimental methods that have been utilized to efficiently measure the polymer-polymer interfacial tension have been briefly reviewed, with emphasis on the static methods (pendant drop, with the approach being very similar to the case of sessile drop) that have been widely used for polymeric liquids. The breaking thread method and the IFR method have been frequently used as weU, especially for high molecular weight polymers. 

The interfacial tension at the interface between two polymers is an expression of different energetics of bulk materials. It reflects differences in thermodynamics, which are related to the x parameter, as shown by Eq. (3.4). The experimental evaluation of the interfacial tension with polymeric melts is extremely difficult due to problems associated with sample preparation and equilibration [77, 78]. Several techniques have been proposed for the measurement. The most commonly used techniques include the pendant drop method, the embedded fiber retraction technique, and the breaking thread method. Classical equilibrium interfacial tension experiments like the pendant drop technique are very difficult to apply to high polymers because of their high melt viscosities (10 -10 Pas). There are many practical problems associated with the pendant drop technique ... 

Even small amounts of reaction have been found to greatly reduce the interfacial tension between polymers. Sundararaj [35] used the breaking thread method to measure... 

Many of the compatibihzation studies include interfacial tension measurements and several examples wiU be noted here. The interfacial tension of LDPE/PA6, determined by the breaking thread method, was measured with the addition of various compatibilizers, including poly(ethylene-co-acrylic acid), poly(ethylene-co-acrylic acid Zn + salt), styrene-ethylene/butylene-styrene (SEES) block copolymer with and without maleic anhydride functionalization [246]. The SEES block copolymer without MA showed no reduction in interfacial tension, whereas the other compatibilizers exhibited significant reductions. 

Another method to determine the interfacial tension of immiscible polymer blends is termed the breaking thread method. Thin fibers (in the range of 10s of pm) are embedded in a matrix polymer. Heating to the viscous liquid state results in sinusoidal fiber distortion, ultimately yielding regularly dispersed elKpsolidal to spherical domains as shown in Fig. 5.35. The amplitude, a, follows an exponential relationship ... 

DDRM is particularly useful for the binary polymer blends. The dynamic interfacial tension coefficient, Vj2, is determined from the time evolution of a distorted fluid drop toward its equilibrium form. Measurements of either low viscosity model systems or high viscosity industrial polymer mixtures led to a good agreement with values obtained from the widely used breaking thread method. DDRM enables to measure in polymeric blends of commercial interest — the high viscosity systems that frequently are impossible to characterize by other techniques. Furthermore, for the first time it is possible to follow the time dependence of Vj, thus unambiguously determine its dynamic and equilibrium values. 

Measurements of interfacial tensions of polymer melts were reviewed by Wu (55), Koberstein (65), and Demarquette (66). The measurements usually need long equilibrium time because of the high viscosities of polymer melts. The measurements can be divided into two groups static methods in which interfacial tension is calculated based on the equilibrium profile of the drops and dynamic methods that study the evolution of fiber or drop profiles with time. Static methods include pendant drop method, sessile drop method, and rotating drop method. Dynamic methods include breaking thread method, imbedded fiber method, and deformed drop retraction method. 

Xing et al. (2000) compared five different techniques for the measurement of interfacial tension in a model polystyrene (PS)/polyamide-6 (PA-6) system at a constant temperature. The techniques include three dynamic methods (the breaking thread, the imbedded fiber retraction, and the retraction of deformed drop), one equilibrium method (the pendant drop), and a rheological method based on linear viscoelastic measurements. The advantages, the limitations, and the difficulties of each technique were discussed and compared. 

Palmer G, Demarquette NR (2003) New procedure to increase the accuracy of interfacial tension measurements obtained by breaking thread method. Polymer 44 3045—3052... 

Breaking Thread Method for Interfacial Tension Determination Figure 5.35 Breaking thread method for the determination of interfacial tension of polymer blends... 

A wide range of experimental techniques has been proposed through the years to measure the interfacial tension. Most popular has been the pendent drop technique but there has been increasing interest in techniques based upon breaking molten polymer threads. Methods of measurement of interfacial tension are summarized in Table 6.1 and values of the interfacial tension for different polymer-melt pairs are summarized in Table 6.2. The larger the polarity difference is, the larger the interfacial tension. Thus the greatest interfacial tension in Table 6,2 is for polyethylene and polyamide 6,... 

The associated process for the Finite Element Method is slightly different and in consequence is referred to in the present document as a threads analysis. The process requires breaking down the analysis into a set of stages and for each stage applying an algorithm which identifies discrete steps together with inputs/outputs. Table 1 shows how the threads process applies to the external part of the analysis process in which the real world is converted into an idealised finite element model. 

Amines have also been microencapsulated within small cellulosic or polyelectrolyte capsules. This is a method for keeping the amine separate from the epoxy resin during storage. When the user decides to initiate cure, the capsules are broken, usually in the application process, and the amine is free to react with the epoxy resin. A successful example of this type of product is an epoxy adhesive that can be preapplied to machine screw threads. When the screw is ultimately threaded into place, the shearing action causes the capsule to break. Bond strengths are generally low for this type of adhesive, but this may not be important in certain applications. 

---