Thermal degradation properties of solid polymer electrolyte (poly(vinyl alcohol)+phosphoric acid)/methylene blue composites Prakash R. Somani a, *, R. Marimuthu a , A.K. Viswanath a , S. Radhakrishnan b a PhotonicsandAdvancedMaterialsLaboratory,CentreforMaterialsforElectronicsTechnology(C-MET), Panchawati, OffPashanRoad, Pune-411008, India b Polymer Science and Chemical Engineering, National Chemical Laboratory (NCL), Pashan Road, Pune 411 008, India Received 3 April 2002; received in revised form 5 July 2002; accepted 23 July 2002 Abstract The thermal stability and degradation of poly(vinyl alcohol) (PVA), PVA+H 3 PO 4 (solid polymer electrolyte, SPE), PVA con- taining methylene blue (MB) dye and SPE (PVA+H 3 PO 4 )+MB were studied by TG/DTA/DTG and DSC techniques. The FTIR and UV–vis study of these materials indicates that MB forms a complex with the polymer by a hydrogen bonding interaction between the –OH group of the polymer and the nitrogen of MB and improves the thermal stability of the polymer. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Poly(vinyl alcohol) (PVA); Methylene blue (MB); Thermal degradation properties; Solid polymer electrolyte 1. Introduction Poly(vinyl alcohol) (PVA) has been widely used as a solid polymer electrolyte (SPE) (when doped with phosphoric acid (H 3 PO 4 ) in solid state electrochromic displays (ECD), solid state photocells [1–5], as a steric stabilizer for producing conducting polymer dispersions [6–7] etc. Recently, Whang et. al. have used poly(- phenylene vinylene) (PPV)–PVA-based polymers as emissive layers in polymeric light emitting diodes (LED). He has shown that by adjusting the weight ratios of PPV and PVA, a series of PPV–PVA- polymers can be obtained with different p-conjugated chain lengths. Hence, the light emission can be tuned from yellow-green to blue [8]. PVA is also used as a hydrogel [9]. PVA is known to form blue complexes with iodine and has been studied extensively [10]. In our earlier studies, we have demonstrated that when complex- forming dyes like crystal violet (CRV), methylene blue (MB) and rhodamine B (RB) are incorporated into SPE (i.e. PVA+H 3 PO 4 ), the films of such materials show interesting and promising humidity dependent optical properties and can be used for optical detection of humidity [11,12]. The wider applicability of PVA is because of its unique chemical and physical properties. These properties come from its hydroxyl group. The hydrogen bonding between hydroxyl groups plays an important role in determining the properties of PVA— for example, high water solubility, a wide range of crystallinity, and high crystal modulus [13]. Study of thermal degradation of PVA and its composites and/or blends is the subject of several publications [14–17]. In the present work, the thermal stability and degra- dation of PVA, PVA+H 3 PO 4 (SPE), PVA containing MB dye and SPE (PVA+H 3 PO 4 ) containing MB is studied by TG/DTA/DTG and DSC techniques. FTIR and UV–vis studies on these materials indicate that MB dye forms a complex with the polymer by a hydrogen bonding interaction between the –OH group of the polymer and the nitrogen of MB and improves the thermal stability of the polymer. 2. Experimental Poly(vinyl alcohol) (PVA, MW 10 4 , Loba Chemie) along with phosphoric acid (H 3 PO 4 , 1:1) was dissolved in distilled water (1 wt.%) to which methylene blue 0141-3910/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0141-3910(02)00240-9 Polymer Degradation and Stability 79 (2003) 77–83 www.elsevier.com/locate/polydegstab * Corresponding author. Permanent address: Near Agasti Theatre, At-Po.-Tal-Akole, Dist. A. Nagar, Via. Sangamner, Akole-422601, Maharashtra, India. Tel.: +91-02424-22620. E-mail addresses: psomani_cmetp@yahoo.com, psomani1@ yahoo.com (P.R. Somani).