The natural fiber (NF) reinforced composites, so called eco-composites, are subject of many scientific and research projects, as well as many commercial programs. The growing global environmental and social concern, high rate of depletion of petroleum resources, and new environmental regulations have forced the search for new composites and green materials, compatible with the environment. The aim of this article is to present a brief review of the most suitable and commonly used biodegradable polymer matrices and NF reinforcements in eco-composites, as well as some of the already produced and commercialized NF eco-composites. POLYM. COMPOS., 28:98 -107, 2007.

BACKGROUND:The high esthetic expectations from the prosthodontic restorations have directed the qualitative development of the materials towards the all-ceramic materials that are capable of replacing porcelain-fused-to-metal systems.AIM:This article reviews the literature covering the contemporary all-ceramic materials and systems with a focus on the chemical composition and materials’ properties; also it provides clinical recommendations for their use.RESULTS:The glass-matrix ceramics and polycrystalline ceramics are presented, as well as recently introduced machinable materials, all-zirconia and resin-matrix ceramics. The specific properties of zirconia, such as transformation toughening, stabilisation of the crystallographic structure, low-temperature degradation and factors affecting the zirconia’s ageing, are emphasised.CONCLUSION:The favourable properties of the resin-matrix ceramics, such as modulus of elasticity similar to dentin, shock-absorbing characteristics and high resilience and fracture resistance, are also covered in this article.

Poly(L-lactic acid)-titanium dioxide nanocomposites (with various loadings of TiO 2 : 0.5, 1, 2, 5, and 10 wt %) were produced by solution casting method. The influence of TiO 2 on thermal properties and crystallinity of PLA was investigated by DSC and FTIR spectroscopy. The TiO 2 nano filler has no significant influence on the characteristic temperatures (T g , T c , and T m ), but has high impact on the crystallinity of these systems. The degree of crystallinity X c significantly increases for PLA nanocomposites loaded with up to 5 wt % of TiO 2 , while for 10 wt % load of TiO 2 it drops below X c of the pure resin. The degradation of the prepared composites was evaluated hydrolytically in 1N NaOH, enzymatically in a-amylase solutions, and under UV irradiation. The catalytic effect of TiO 2 nano particles on the degradation processes under UV light exposure (k ¼ 365 nm) and hydrolytic degradation was confirmed with the increase of the filler content. The opposite effect was identified in enzymatic degradation experiments.

Biodegradable thermoplastic-based composites reinforced with kenaf fibers were prepared and characterized. Poly(lactic acid) (PLA) was selected as polymeric matrix. To improve PLA/fibers adhesion, low amount of a proper reactive coupling agent, obtained by grafting maleic anhydride onto PLA, was added during matrix/fibers melt mixing. Compared with uncompatibilized composites, this compatibilization strategy induces a strong interfacial adhesion and a pronounced improvement of the mechanical properties.

In recent years bio-based polymer composites have been the subject of many scientific and research projects, as well as many commercial programs. Growing global environmental and social concern, the high rate of depletion of petroleum resources and new environmental regulations have forced the search for new composites and green materials, compatible with the environment. The aim of this article is to present a brief review of the most suitable and commonly used biodegradable polymer matrices and NF reinforcements in eco-composites and nanocomposites, with special focus on PLA based materials.

Biodegradable thermoplastic-based composites reinforced with kenaf fibers were prepared and characterized. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), produced by bacterial fermentation, was selected as polymeric matrix. To improve PHBV/fibers adhesion, low amount of a proper compatibilizing agent, obtained by grafting maleic anhydride onto PHBV, was added during matrix/fibers melt mixing (reactive blending). When compared with uncompatibilized composites, the presence of the compatibilizer induces a stronger interfacial adhesion and a more pronounced improvement of the mechanical properties.

Nanocomposites, based on a poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) matrix and titanium dioxide (TiO 2 ) nanoparticles and fabricated with a solventcasting technique, were characterized with differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. The content of TiO 2 nanoparticles varied between 0.5 and 10 wt %. Degradation studies, including hydrolytic degradation in a strong base medium (1N NaOH) and degradation under ultraviolet light at 365 nm, were performed. It was confirmed that the inorganic filler had no great influence on thermal properties such as the melting and crystallization temperatures. Improved degradation temperatures were also confirmed with the increase in the filler content. Degradation observations confirmed significant increases in hydrolytic erosion with the filler content increasing in comparison with the degradation of a pure PHBV film. Also, the photocatalytic activity of the inorganic filler TiO 2 in all investigated composites [irradiated at k ¼ 365 nm and immersed in a liquid medium (H 2 O)] was evaluated. The degraded samples were analyzed with Fourier transform infrared spectroscopy, which confirmed their increased crystallinity.

AIM:The purpose of this review is to represent acids that can be used as surface etchant before adhesive luting of ceramic restorations, placement of orthodontic brackets or repair of chipped porcelain restorations. Chemical reactions, application protocol, and etching effect are presented as well.STUDY SELECTION:Available scientific articles published in PubMed and Scopus literature databases, scientific reports and manufacturers’ instructions and product information from internet websites, written in English, using following search terms: “acid etching, ceramic surface treatment, hydrofluoric acid, acidulated phosphate fluoride, ammonium hydrogen bifluoride”, have been reviewed.RESULTS:There are several acids with fluoride ion in their composition that can be used as ceramic surface etchants. The etching effect depends on the acid type and its concentration, etching time, as well as ceramic type. The most effective etching pattern is achieved when using hydrofluoric acid; the numerous micropores and channels of different sizes, honeycomb-like appearance, extruded crystals or scattered irregular ceramic particles, depending on the ceramic type, have been detected on the etched surfaces.CONCLUSION:Acid etching of the bonding surface of glass - ceramic restorations is considered as the most effective treatment method that provides a reliable bond with composite cement. Selective removing of the glassy matrix of silicate ceramics results in a micromorphological three-dimensional porous surface that allows micromechanical interlocking of the luting composite.