Nanomechanical Properties of Poly(trimethylene malonate) and Poly(trimethylene itaconate) During Hydrolytic Degradation Ersan Eyiler, 1 I.-W. Chu, 2 Mathew D. Rowe, 2 Keisha B. Walters 2 1 Department of Chemical Engineering, Cukurova University, Ceyhan, Adana 01950, Turkey 2 Dave C. Swalm School of Chemical Engineering, Mississippi State University, Mississippi State, Mississippi 39762 Correspondence to: K. B. Walters (E - mail: kwalters@che.msstate.edu) ABSTRACT: The aim of this work was to evaluate surface mechanical properties of two bioplastics, poly(trimethylene malonate) (PTM) and poly(trimethylene itaconate) (PTI), during hydrolytic degradation. Renewable resource-based PTM and PTI were synthe- sized from 1,3-propanediol (PDO), malonic acid (MA), and itaconic acid (IA) via melt polycondensation. The hydrolytic degradation was performed in deionized (DI) water (pH 5.4) at room temperature. Morphology and surface mechanical properties at the nano- scale were monitored by atomic force microscopy (AFM) using a quantitative nanomechanical property mapping mode as a function of degradation time. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to show shifted phase transitions depending on the degradation. DSC studies showed hydrolytic degradation induced crystallinity for PTI. After degradation for one week, the degree of crystallinity had significantly increased, and the elastic modulus of PTI had decreased by 58%. PTM was found to be hygroscopic. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41069. KEYWORDS: biopolymers and renewable polymers; degradation; differential scanning calorimetry (DSC); mechanical properties; polyesters Received 14 October 2013; accepted 12 May 2014 DOI: 10.1002/app.41069 INTRODUCTION Polymers are good substitutes for metal, paper, and glass since they demonstrate suitable energy savings, weight savings, and/or durability. Bioplastics are polymeric materials produced from biomass-derived monomers, and also often can be biologically and/or hydrolytically degradable. Polyhydroxyalkanoates, poly (lactic acid), poly(glycolic acid), polysaccharides, vegetable- derived polymers, and poly(orthester) are just a few examples of different bioplastic types/classes. 1–5 These plastics span a range of physicochemical properties, cost, and degradation rates, and have the potential to compete with petroleum-based plas- tics in terms of properties and cost. 6–11 Biorefineries that produce multiple products, including higher- value chemicals as well as fuels and power, have become signifi- cant advancement toward reducing fossil fuel dependency. For this reason, in 2004, the U.S. Department of Energy (DOE) identified 12 building block chemicals derived from sugars that can serve as key feedstocks for future biorefineries due to their functionality, availability, toxicity, and possible derivatives. 12 These chemicals and their derivatives have the potential to be biomonomers used for production of bioplastics. Using several monomers from the DOE 12 building blocks list, two bio-based copolymers, poly(trimethylene malonate) (PTM) and poly(trimethylene itaconate) (PTI), have been produced with ester bonds incorporated into the polymer backbone to facilitate hydrolytic and/or enzymatic degradation as described previously. 13 PTM was synthesized from 1,3-propane diol and malonic acid to produce a linear copolymer, and PTI was syn- thesized from 1,3-propane diol and itaconic acid to produce a branched and possibly cross-linked copolymer. For specialty applications, the hydrolytic behavior of these bioplastics needs to be evaluated with mechanical properties. In this article, we present a hydrolytic degradation study in deionized (DI) water, addressing this purpose. Weight change was monitored as a function of degradation time (10–10,000 min). More impor- tantly, effects of hydrolytic degradation on the surface mechani- cal properties were examined by atomic force microscopy (AFM) at the nanoscale. EXPERIMENTAL Materials Malonic acid (MA, 99%), itaconic acid (IA, 99%) and chloro- form (98%) were used as received from VWR. 1,3-Propane diol (PDO, 98%), aluminum chloride (98%), and diethyl ether (>99%) were used as received from Sigma-Aldrich. Poly(trimethylene malonate) (PTM) and poly(trimethylene itac- onate) (PTI) were synthesized via melt polycondensation as V C 2014 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2014, DOI: 10.1002/APP.41069 41069 (1 of 9)