Factorial Optimization of the Effects of Melt-Spinning Conditions on Biodegradable As-Spun Aliphatic–Aromatic Copolyester Fibers. III. Diameter, Tensile Properties, and Thermal Shrinkage Basel Younes, 1,2 Alex Fotheringham 1 1 School of Textiles and Design, Heriot-Watt University, Scottish Borders Campus, Netherdale, Galashiels TD1 3HF, United Kingdom 2 Faculty of Mechanical and Electrical Engineering -Textiles Dep., Damascus University, Damascus, PO.BOX 86, Syria Received 22 November 2010; accepted 25 January 2011 DOI 10.1002/app.34216 Published online 23 May 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: To model the melt-spinning process of bio- degradable as-spun linear aliphatic–aromatic copolyester fibers, a fraction factorial experimental design and appropri- ate statistical analysis for the 32 screening trials involving five control parameters were used. Because of their central role in the production processes and end use textiles, it is important to simulate the mechanical and thermal shrinkage properties of AAC fibers. Concise statistical models of fiber behavior are based on factorial experimental design data. Process’s data are collected, analyzed, and mathematical models created to predict the diameter, tenacity, elongation at break, modulus, and thermal shrinkage of the spun fiber in terms of random variables and their associated probabil- ity distributions. The theoretical regression models obtained form the main source code in the enhanced forecasting pro- gram, which presents the melt-spinning process of aro- matic–aliphatic copolyester fibers. Factorial statistical approaches, based on over indicated region levels of melt- spinning process parameters, are given in terms of assump- tions and theory to produce biodegradable, environmentally friendly fibers for different applications. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 1434–1449, 2011 Key words: modeling; biodegradable; aliphatic–aromatic copolyester fibers; factorial experimental design; mechanical and thermal properties INTRODUCTION Previously, researchers’ work has been conducted to improve and characterize biodegradable aliphatic– aromatic copolyesters. 1–10 Aliphatic–aromatic copo- lyesters (AACs) are made from petroleum with sta- ble physical and chemical properties while leaving no environmental footprint. 11 In an active microbial environment, the copolyesters’ products become in- visible to the naked eye within 12 weeks. 12 AACs are potential candidates to make fibers for various nonwoven materials particularly for expendable uses in medicine 13–15 and agriculture. 16–20 As it is difficult to design and produce a manufac- tured product, the experimental design technique is a useful practice for designing new, consistent, and economical products. 21 Measurement, feedback and adjustment, prediction, and correction are the main elements in online quality control. 22,23 Practical soft- ware-based approaches meet with customer require- ments and expectations for reducing the target value variation in processes 24–26 and saving time and cost. 27 Statistical experimental design (SED) is still limited because of poor attitude toward the SED strategies and lack of collaboration between aca- demic and industrial fraternities. 28 As spun fibers should have a structure that can be drawn easily, the stress–strain behavior can also be used to qualitatively describe and classify the poly- mer and its fibers properties and behavior. The % of fiber extension could be limited by crosslinking of the polymer structure, which will affect the biodegrad- ability of the fibers. 29 As the continuous filament yarn has the same number of fibers in the cross section, physicomechanical properties will be influenced uni- formly by constant stretching the fibers through or af- ter spinning 30 ; a high degree of extension gives higher tenacity together with lower elongation at break (high modulus) and vice versa. 31 The increased modulus and tensile strength could be related to the increasing of down draw ratio. A balance between the improvement of mechanical properties and the biodegradability needs to be investigated. 32 Textile fibers with thermoplastic properties have created the need for the testing of thermal shrinkage or extension of yarns and fabrics made from such materials when subjected to heat. Many important physical properties are affected when fibers are set. Correspondence to: A. Fotheringham (a.f.fotheringham@ hw.ac.uk). Journal of Applied Polymer Science, Vol. 122, 1434–1449 (2011) V C 2011 Wiley Periodicals, Inc.