608 Research Article Received: 28 October 2010 Revised: 25 November 2010 Accepted: 26 November 2010 Published online in Wiley Online Library: 6 January 2011 (wileyonlinelibrary.com) DOI 10.1002/jctb.2563 Paulownia as a raw material for the production of pulp by soda – anthraquinone cooking with or without previous autohydrolysis Juan Carlos Garc´ ıa, a Minerva Ana Maria Zamudio, a Antonio P ´ erez, a Hugo Eduardo De Alva b and Francisco L ´ opez a∗ Abstract BACKGROUND: A central composite experimental design and multiple regression were used to model the production of pulp and paper sheets from a Paulownia fortunei × tormentosa × elongata trihybrid clone. Also, the same experiments were carried out with the solid phase after autohydrolysis of the raw material. RESULTS: The results were compared with those obtained from the solid phase remaining after autohydrolysis of the raw material with a view to optimizing the use of hemicelluloses and cellulose by fractionation. Pulp and paper sheets from the trihybrid clone surpass those from other Paulownia species such as P. fortunei and P. elongata in physical properties such as tensile index (11.6–49.1 Nm g −1 ), burst index (0.23–2.41 MPa m 2 kg −1 ), tear index (0.71–3.03 mN m 2 g −1 ) and intrinsic viscosity (427 – 958 cm 3 g −1 ). CONCLUSIONS: The solid phase obtained by autohydrolysis of the Paulownia trihybrid provides pulp and paper sheets comparable in strength-related properties with those of pulp directly produced from the raw material, but using substantially milder operating conditions and with the added advantage that the autohydrolysis treatment provides highly valorizable liquor. c  2011 Society of Chemical Industry Keywords: Paulownia; autohydrolysis; soda – AQ pulp; paper INTRODUCTION The genus Paulownia originated in China, where it has been a traditional tree for more than two thousand years. Because it has modest water requirements, Paulownia has aroused interest as an industrial raw material despite the difficulty growing it in marginal areas. 1,2 The genus encompasses nine different species most of which exhibit very fast growth and can be harvested only 15 years after planting to obtain products with a substantial added value. 3 Paulownia plants have a high biomass production and resprouting potential: up to 50 ton ha −1 yr −1 , which is among the highest reported figures (especially in relation to annual crops). 4 Also, they exhibit fast growth and can produce as much biomass in one year as other species in several years. 5 Under favourable conditions, an intensive plantation of 2000 trees ha −1 can yield up to 150–300 ton wood yr −1 only 5–7 years after planting. 6 As shown in this work, high biomass production can be further increased by using hybrids of some varieties. Thus, the Paulownia fortunei – Paulownia tormentosa clone used by Ayan et al. (2006) 7 grew up to 76.2 cm within 1 year after direct seeding. The genus Paulownia has lately been introduced and naturalized in a number of countries including the USA, and has been the subject of study as regards adaptation to soil and survival of diverse varieties in some areas. 7–9 This work is novel because there are few references to industrial uses of Paulownia. There are, however, a number of agronomic, genetic and health-related studies about this genus. Worth special note among them are those suggesting the potential advantages of its use in energy crops by virtue of its favourable energy input/output ratio and biomass production. 10,11 Other suggested uses for Paulownia included veneer or plywood, furniture, handicrafts, tools, musical instruments, particleboard, charcoal and there have been attempts to generate energy from paulownia chips. 3,12 – 14 One of them is its use as source for pulp. The most suitable variety of Paulownia for this purpose is Paulownia Fortunei, 15 characterized by fast development and uniform and regular growth. 12 Also, this plant could be susceptible to producing xylooligomers under a hydrolytic process, as well as provide a low degraded lignocellulosic residue to the pulping process, which is justified by some Paulownia characteristics, such as its growth and physicochemical properties. 16,17 ∗ Correspondence to: Francisco L´ opez, Departamento de Ingenier´ ıa Qu´ ımica, Facultad de Ciencias Experimentales, Universidad de Huelva, Campus del Carmen, Avda. 3 de marzo s/n. 21071, Huelva, Spain. E-mail: baldovin@uhu.es a Chemical Engineering Department. Facultad de Ciencias Experimentales Campus del Carmen, Universidad de Huelva, Avda. 3 de marzo S/N, 21071 Huelva, Spain b Instituto Tecnol´ ogico de Ciudad Madero. Tamaulipas, M´ exico J Chem Technol Biotechnol 2011; 86: 608–615 www.soci.org c  2011 Society of Chemical Industry