tion rates and greater immobilization generated by surface residues (Rice and Smith, 1984).

Solid polymeric matrices based on xanthan and chitosan and using KNO 3 as a model agrochemical were prepared by direct compression, with a view to evaluating their potential as controlled-release fertilizers (CRFs). The swelling behavior, surface characteristics, and durability in soil of the tablets were studied. The release data were treated with a power law model in order to understand the delivery kinetics of KNO 3 . This proved to be non-Fickian diffusion, with release exponents ranging from 0.80 to 0.88, highlighting the importance of polymer relaxation on drug release. The presence of drug-free surface layers was an important factor in modulating the release. When comparing experiments without and with stirring, the release time ratios between them were as high as 40, predicting a significantly greater release time in soils. In durability experiments in soil, the polymeric matrices lasted longer than 6 weeks. These results show that layered xanthan and xanthan-chitosan matrices perform as a promising system for developing CRFs.

Polymeric matrices based on hydroxypropyl methylcellulose (HPMC) with xanthan (X) or chitosan (Q) and using KNO 3 as a model fertilizer were prepared as three-layered tablets and assayed as controlled release fertilizers (CRFs). The dynamic swelling behavior was analyzed in order to interpret the water uptake mechanism, which in general proved to be non-Fickian. The presence of HPMC allows a substantially constant rate of fertilizer release. The release mechanism of KNO 3 was analyzed and can be described as non-Fickian diffusion, with release exponents ranging from 0.85 to 1.01, suggesting polymer relaxation as the major process controlling fertilizer release. Durability in soil indicates the blend Q-HPMC as the more long-lasting matrix of those tested, remaining at least 34 weeks. Both blends improve HPMC properties for agronomical applications, with X-HPMC increasing the swelling rate and Q-HPMC extending the permanence in the soil. Therefore, layered X-HPMC and Q-HPMC matrices can be proposed as suitable materials for the development of CRFs.

In the present work, solid-state drawing of commercial PLA-based extruded filaments was investigated. Two different filaments were used: one based on neat PLA and the other based on PLA filled with copper particles. The effect of the processing parameters such as the drawing temperature and the draw ratio on the materials morphology and thermal and mechanical behavior was analyzed. A specially designed device which simulates the solid-stated drawing stage frequently used for fibers manufacturing was applied. The drawing effects were evidenced by the results of the degree of crystallinity and tensile parameters, as well as by SEM analysis and topographical observations of the surfaces of the filaments. From these results, it was concluded that the draw ratio is more important than the drawing temperature as a determining factor of the tensile performance of the PLA-based filaments investigated. However, the drawing temperature plays a key role to establish the critical draw ratio to obtain stable solid-state drawing.