Miscibility Behavior of Poly Ethylene Glycol or Poly Ethylene Succinate/Chlorinated Poly Vinyl Chloride Blends Studied by Dielectric Relaxation Spectroscopy

Taha A. Hanafy

Department of Physics, Faculty of Science, Tabuk University, Tabuk, KSA.

DOI: 10.4236/ampc.2013.32015                

Abstract

The miscibility of chlorinated poly vinyl chloride (CPVC) and poly ethylene glycol (PEG) or poly ethylene succinate (PES) had been investigated using dielectric relaxation spectroscopy (DRS) over frequency and temperature ranges; 10 kHz - 4 MHz and 300 - 450 K, respectively. Three relaxation processes namely ρ-, α’-, and α-relaxation processes were observed for tan(δ) and the electric modulus M" of pure components and blends. The first one was attributed to the space charge polarization or the Maxwell-Wagner polarization. The second one was related to the amorphous regions located between the lamellar crystal stacks. The third one was due to the micro-Brownian motion of CPVC main chains. This process was found to be dependent in respect of temperature and frequency. The molecular dynamics of α-relaxation process were influenced by blending, i.e., the dielectric strength (De), the peak broadness, and the peak maximum of tan(δ) were found to be compositional dependent. Electric modulus analysis reveals that there is a role of electrode polarization for the dielectric relaxation.

Keywords

Miscibility; Dielectric Relaxation; Electric Modulus; Blending

1. Introduction

Biodegradable polymers have recently received more attention from the view point of environment protection and resource. Biodegradable polymers can usually be classified into two categories. One is the biosynthetic polymers, such as bacterial Poly(3-hydroxybutyrate) (PHB) [1]. The other is the chemosynthetic polymers such as poly ethylene glycol (PEG) and the poly ethylene succinate (PES) as aliphatic biodegradable polyester. The crystal structure, morphology and melting behavior of PES have been reported [2-4]. The chemical structure of PEG and PES are

and

, respectively.

PEG is used in most of the applications of aqueous phase partitioning. PEG is biocompatible and biodegradable polymer and has adhesive and flocculent properties [5]. Blend of PEG or PES with other polymers has been studied in order to modify the physical properties and extend its practical applications. Till now, less work has been done on blending PEG or PES with other polymers such as PVC or CPVC.

It is well known that miscibility and crystallization behaviors play crucial roles in physical properties of polymer blends. The most common and particularly important miscible polymer owes hydrogen bonding and electrostatic interactions between the different groups on the polymeric structure of the components. The weak hydrogen bond is postulated between halogen-containing polymers, such as PVC or CPVC, and the oxygen containing polymers [6]. This type of interaction is responsible for the miscibility of various polymers [7-9]. CPVC contains a higher content of chlorine groups and a higher α-hydrogen than PVC. Consequently, CPVC may have a wider miscibility window than PVC when blending with other polymers [10-12]. The compatibility of many PVCbased blends has been reported by the detected of glass rubber transition, Tg, which involves solid-state analysis. In the amorphous phase of polymers, there are two main chain motion; micro-Brownian motion, which occurs at Tg, and a more local type of motion, which occurs in the glassy state. The study of the amorphous loss (α) provides the most reliable means of assessing miscibility in polymer blends. In binary blend, relaxation process is based on the occurrence of either one or multiple loss peaks [7]. A single α-relaxation peak correspond a miscible blend.

It is possible to identify low cost and rapid techniques to study the miscibility of polymer blends. The main method to find out the number of the amorphous phases in polymer blends is the determination of the number of Tg because each Tg corresponds to one amorphous phase. Different experimental techniques including different scanning calorimetry (DSC), dynamical mechanical thermal analysis (DMTA) and dielectric relaxation spectroscopy (DRS) are used for the determination of Tg [13].

DRS is used to probe long and short range motions of macromolecular motions of mobile charges as a function of both frequency and temperature. Several researchers have been used DRS to examine the degree of miscibility in polymer blends [14-16]. Peak shifts and broadening are commonly observed for miscible or partially miscible polymer blends. It has been found that miscible polymer blends exhibit single Tg and one loss curve in dielectric or mechanical measurements. However, Alegria et al. [17] found that miscible blends of cis-polyisoprene (PI) and poly vinyl ethylene (PVE) exhibit biomodal dielectric loss curves for α-relaxation process. Biomodal means that a loss curve exhibits two peaks or a main peak and shoulder.

This study was aimed at exploring the miscibility and phase behavior of CPVC-PEG and CPVC-PES blends by using DRS technique. Because C-Cl, OH, C=O and ether groups have a strong dipole moment, relaxation processes of these blends can be examined with dielectric measurements. Subsequently, the dielectric data can also give hints about the molecular interaction in such blends.

2. Experimental

2.1. Materials

CPVC used in this work was obtained from Goodrich Chemical Division with M_w = 119,000, Tg = 352 K and it contains 67.2 wt% chlorine, PEG (M_w = 5400 and Tg = 208 K) was supplied from British Drug Houses Ltd. (BDH) and PES was obtained from Aldrich Chemical Co with M_w = 22,000 and Tg = 225 K.

2.2. Method

Blend of CPVC and PEG or PES was prepared by slowly casting film from tetrahydrofuran (THF, Aldrich) solutions as follows: An aqueous solution was obtained by adding 1 g of PVC to 20 mL of THF and the heating of the mixture to 40˚C with continuous stirring. PEG or PES of 10 wt% was dissolved in 5 ml of THF at 40˚C. The mixture was added to the CPVC solution at 40˚C with continuous stirring of the final mixture for 8 h. The aqueous solution of the mixture was cast into a Petri dish placed on a leveled plate at room temperature (30˚C) for 7 days until the solvent was completely evaporated. The obtained polymer film, 0.08 mm thick, was cut into square pieces and coated with silver paste to achieve ohmic contacts.

2.3. Dielectric Measurements

The dielectric measurements were carried out with a Hioki (Ueda, Nagano, Japan) model 3532 High Tester LCR, the accuracy of which for measuring the capacitance was of the order of ±0.08%. The dielectric constant (e'), and dielectric loss index (e") were recorded at frequency and temperature ranges 10 kHz - 4 MHz and 300 - 450 K, respectively. Both e' and e" were calculated as follows:

(1)

where c is the capacitance of the sample filled capacitor, d is the sample thickness, e_o is the vacuum permittivity, and A is the electrode area. The temperature was measured with a T-type thermocouple with its junction just in contact with the sample with accuracy better than ± 1 K.

3. Results and Discussion

3.1. Dielectric Relaxation of CPVC

Figure 1(a) shows the frequency dependence of dielectric loss tan(δ) for Pure CPVC sample at some fixed tem-

(a)(b)

Figure 1. (a) The frequency dependence of dielectric loss tan(δ) for pure CPVC at some fixed temperatures. (b) The temperature dependence of dielectric loss tan(δ) for pure; CPVC at some fixed frequencies.

peratures. The variation of tan(δ) with frequency gives evidence for a very distinct dipolar peak whose position depends on the ambient temperature. Obviously, three relaxation processes can be observed for tan(δ). The high frequency side process, at 560 kHz, is related to the main α-relaxation process. The origin of this process is the micro-Brownian cooperative motion of the CPVC main chain. This behavior is connected with the onset of largescale motion of the main chain segments in the vicinity of Tg of CPVC. The loss maximum peak of this process shifts to a higher frequency with increasing in temperature. This indicates that the dielectric process for peak is dipolar in nature [7]. The middle frequency side, at 80 kHz, is α’-process. This effect can be assigned to the cooperative motions of CPVC end groups [7] or the segmental motion of the branching that occurs between CPVC main chains. This will form a rigid amorphous phase between adjacent lamellae within the lamellar stacks of CPVC. The low frequency side, at 10 kHz, is the ionic conductivity or ρ-relaxation process. This process appears at higher temperature as a rapid increase in tan(δ). This effect attributes to the existence of space charge polarization and the free charge motion within the material and also related to so called conductivity current relaxation process [18,19].

Figure 1(b) depicts the temperature dependence of tan(δ) for pure CPVC sample at some selected frequencies. It is clear that, tan(δ) for CPVC sample undergoes only α-relaxation process at 405 K. This process is related to Tg of CPVC. The peak maximum of α-process shows an increase in its magnitude with the increase of temperature as a result of the micro-Brownian motion of CPVC main chains. Moreover, α-relaxation process peak can be ascribed to the release of the frozen-in dipolar C-Cl groups and their cooperative motion with adjoining segments of the main chain [20].

Conflicts of Interest

The authors declare no conflicts of interest.

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