Waterborne acrylic hybrid adhesives based on a methacrylate-functionalized porous clay heterostructure for potential lam
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Mark D. Soucek Department of Polymer Engineering, The University of Akron, Akron, Ohio 44325, USA
Hathaikarn Manuspiyaa) The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok 10330, Thailand; and Center of Excellence on Petrochemical and Materials Technology, Bangkok 10330, Thailand (Received 18 March 2017; accepted 26 July 2017)
A new waterborne acrylic (WAC) hybrid adhesive was evaluated for an untreated polypropylene lamination. The WAC hybrid adhesive was formulated with a new class of porous clay heterostructure (PCH), which was modified with 3-(trimethoxysilyl)propyl methacrylate (as a coupling agent) to promote chemical bonding with the acrylic matrix to form a methacrylate-functionalized PCH (MPCH). The WAC hybrid adhesive was based on copolymers (2-ethylhexyl acrylate, ethylene glycol methyl ether acrylate, 2-(hydroxyethyl) methacrylate, styrene and acrylic acid) with varying amounts of MPCH. The scanning electron microscopy micrographs revealed the presence of a well dispersed MPCH distributed throughout the matrix. The optimal adhesive performance, in terms of the 180° peel strength of bonded joints, of 140.2 N/m was achieved using 1.5 wt% of MPCH, while the thermal stability of the adhesives was improved with increasing MPCH loading levels.
I. INTRODUCTION
Solventborne laminating adhesives are dominant in the manufacturing processes especially for flexible packaging. However, as highlighted by the Environmental Protection Agency, the volatile organic compound emissions from anthropogenic sources are in urgent need of restriction, since they are hazardous air pollutants.1 As a consequence, waterborne acrylics (WACs) are currently being explored as a replacement for the solventborne adhesives. These adhesives offer excellent durability, optical clarity, ultraviolet (UV) resistance, toughness, and oil tolerance.2–4 However, on occasion waterborne adhesives have been reported to have a catastrophic loss of adhesion, resulting in a failure of bonded joints.5 Thus, new approaches are needed for the waterborne adhesives to replace the solventborne systems. As one possible solution to the serious debonding problem, WAC adhesives based on an organic/inorganic hybrid structure are being developed.6 Generally, a small percentage (less than 5 wt%) of nanoinorganic fillers, including clay mineral,7–9 titania,10
Contributing Editor: Sarah Morgan a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.332
alumina,11,12 nanosilica,13,14 and calcium carbonate,15 are mechanically blended into the adhesives resulting in dramatic enhancement of the adhesive properties with clay being the most favorable. In case of pressuresensitive adhesives (PSAs), Bonnefond et al. studied the morphology and properties of the waterborne films from n-butyl acrylate/methyl methacrylate/ montmorillonite clay (MMT) hybrid adhesives.16 The peel resistance increased for the formulations containing MMT. The most remarkable result was obtained for 2% weight based on monomers (wbm
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