Poly(lactide acid) Composites Reinforced with Fibers Obtained from Different Tissue Types of Picea sitchensis A. Gregorova, 1 M. Hrabalova, 2 R. Wimmer, 3 B. Saake, 4 C. Altaner 5 * 1 Department of Material Sciences and Process Engineering, Institute of Wood Science and Technology, University of Natural Resources and Applied Life Sciences, Vienna A-1190, Austria 2 Department of Agrobiotechnology, Institute for Natural Materials Technology, IFA-Tulln, University of Natural Resources and Applied Life Sciences, Tulln A-3430, Austria 3 Wood Technology and Wood-Based Composites Unit, Faculty of Forest Sciences and Forest Ecology, Georg-August-University Go ¨ttingen, Go ¨ttingen D-37077, Germany 4 Johann Heinrich von Thu ¨ nen-Institut, Federal Research Institute for Rural Areas, Forestry and Fisheries, Institute of Wood Technology and Wood Biology, Hamburg 21031, Germany 5 Department of Chemistry, University of Glasgow, Glasgow, United Kingdom Received 18 March 2009; accepted 22 May 2009 DOI 10.1002/app.30819 Published online 7 July 2009 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Wood fibers vary in their properties across species, across trees of the same species, and within single trees. This work takes advantage of wood fibers reinforc- ing poly(lactic acid) composites that originate from differ- ent tissue types of the species Sitka spruce (Picea sitchensis). Fibers were prepared with high temperature thermo-mechanical processing (TMP) from juvenile, mature, and compression wood tissues of Sitka spruce. Composites were made by solution casting with sub- sequent hot-pressing. Thermal as well as mechanical properties were determined using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and tensile testing. The obtained results showed that the chemical and physical properties of different tissue-type Sitka spruce fibers have significant effects on the thermal and mechanical properties of the Polylactic acid (PLA)/ Sitka fiber composites. To increase interfacial compatibil- ity between the hydrophilic fibers and the hydrophobic polymer matrix, the fibers were treated with vinyltrime- thoxysilane (VTMO), while PLA was modified with 4,4- methylene diphenyl diisocyanate (MDI). It was found that PLA/Sitka composites treated with VTMO and MDI exhibited improved thermal and mechanical properties, compared to the unmodified control. The work also dem- onstrates that there is potential to improve biobased com- posites by utilizing the natural variability of wood fibers. V V C 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 2616–2623, 2009 Key words: biopolymers; composites; mechanical properties; thermal properties; Sitka spruce [Picea sitchensis (Bong.) Carrie `re] INTRODUCTION During recent years, intensive research has been focus- ing on the development of biobased and biodegradable plastics with the intention to reduce environmental pol- lution and to replace petroleum-based plastics. Polylac- tic acid (PLA) is biodegradable hydrolysable aliphatic semi-crystalline polyester produced through direct con- densation of its monomer, lactic acid, followed by a ring opening polymerization of the cyclic lactide dimmer. Lactic acid can be obtained from renewable resources such as saccharide-based materials. 1–3 PLA shows stiffness and strength properties comparable to petroleum-based plastics and can be processed by standard methods such as extrusion, injection molding, thermoforming, or compression molding. 4 Further, PLA is a readily compostable and degradable thermo- plastic polymer. Despite these promising properties, its applicability is restricted by high production costs, brit- tleness, and a low softening temperature. 5 Brittleness can be lowered through incorporation of plasticizers, 6 while production costs can be reduced, and the me- chanical performance of the material modified by the addition of various fillers. The use of renewable and biodegradable fillers such as starch, cellulose, kenaf, hemp, and wood fibers has been investigated inten- sively during the past years. 5,7–12 Wood fibers attracted attention as fillers mainly in polyolefins in the first place because of their Journal of Applied Polymer Science, Vol. 114, 2616–2623 (2009) V V C 2009 Wiley Periodicals, Inc. *Present address: School of Biological Sciences, Faculty of Science, University of Auckland, Auckland 92019, New Zealand Correspondence to: A. Gregorova (adriana.gregorova@ boku.ac.at). Contract grant sponsor: Austrian Science Fund FWF; contract grant number: L319-B16. Contract grant sponsor: SHEFC (Scottish Higher Education Funding Council).