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In this study, a technological procedure for the production of a molding compound based on short carbon fibers and an ablative phenol-formaldehyde resin for high temperature application was optimized. The starting raw materials were characterized and molding compounds with different fiber/ /matrix ratios and different fiber lengths were obtained. From the different laboratory samples, molded parts were made by thermocompression. The basic mechanical and thermal properties of the composites were determined. From the obtained results, the optimal fiber/matrix ratio was determined for a production of molding compound for high temperature application. The molding process of the composite material was optimized and all the parameters for good mechanical properties and high thermal stability of the composite were obtained. Optimization of the composite molding process was performed by the application of a numerical method for a planned experiment, i.e., a full three--factorial experimental design with variance of all three parameters (fiber length, temperature and time of the press cycle) on two levels. The obtained mechanical properties (flexural strength: 247 MPa, modulus: 27.6 GPa, impact resistance: 110 (for test moldings 10 mm×10 mm) and 91 kJ/m 2 (for test moldings 15 mm×15 mm)) justified the application of this composite material in the automotive, leisure, military and other industries where high temperature resistance and high mechanical strength is required.

Renewable raw materials and recyclable thermoplastic polymers provide attractive eco-friendly quality as well as environmental sustainability to the resulting natural fiber reinforced composites. We studied the possibility of using the recycled polypropylene (PP) for production of composites based on kenaf fibers (KF) and rice hulls (RH) as reinforcements. Polypropylene/rice-hulls (PP/ RH/CA) and polypropylene/kenaf (PP/K/CA) composites with 30% fiber (filler) content and appropriate compatibilizing agent (CA)-a maleic anhydride grafted PP (MAPP), have been prepared by two steps procedure: melt mixing and compression molding. Flexural strength and thermal stability of the composites with recycled PP were similar to those with neat PP. The composites reinforced with kenaf fibers have shown better properties than those based on rice hulls. The flexural strength of the composite sample with recycled PP is 51.3 MPa in comparison with 51.1 MPa for the composite with neat PP. Degradation temperatures of neat and composite with recycled PP at residual weight 90% are 344.4 C and 343.5 C, respectively. The results obtained report the possibility of utilization of recycled PP for the production of natural reinforcements based composites with good mechanical characteristics for using as construction building materials in housing systems.

In this study, rice-hull-filled polylactic acid (PLA) biocomposites were prepared through the addition of 5 wt.% PLA-grafted-MA (CA) for the enhancement of adhesion between the polymer matrix and natural filler. The composites containing 30 wt.% rice hulls (RH) were prepared by compression molding, with particular attention given to the introduction of recycled PLA matrix, as well as to the possibility of the recycling and reuse of PLA/RH biocomposites. For all biocomposites, produced from neat polymer and RH and those produced after the recycling of PLA/RH composites, the mechanical and thermal properties were analyzed and compared to those of a commonly used thermoplastic based-polymer, polypropylene (PP), containing the same reinforcement. Thermal stability of biocomposites based on recycled PLA matrix and of the new composites produced from recycled ones was practically unchanged. Introduction of the recycled PLA matrix into biocomposites resulted in decreased flexural modulus and strengths of about 50%. Utilization of the mixture obtained after the thermal-mechanical recycling of the whole biocomposite resulted in a composite with slightly increased flexural modulus and decreased flexural strength.The obtained results have shown that rice-hull-filled poly(lactic acid) biocomposites could be recycled and utilized for the production of new eco-materials with acceptable thermal and mechanical properties. Namely, the results for flexural strength and modulus of the recycled biocomposite samples are comparable to those of conventional formaldehyde wood medium density fiberboards used as construction elements for indoor applications.Keywords: biocomposites; polylactic acid; polypropylene; rice hulls; compression molding БИОКОМПОЗИТИ НА БАЗА НА ПОЛИМЛЕЧНА КИСЕЛИНА И НИВНИ ТЕРМИЧКИ КАРАКТЕРИСТИКИ ПО РЕЦИКЛИРАЊЕПодготвени се биокомпозити полимлечна киселина/оризови лушпи со додавање на 5 % калем-кополимер полимлечна киселина-ко-малеински анхидрид, PLA-graft-MA, како компати-билизатор за подобрување на атхезијата помеѓу полимерната матрица и природното полнило. Композитите со 30 % оризови лушпи (RH) беа подготвени по пат на пресување, при што особено внимание е посветено на внесување рециклирана полимлечна киселина, како и на можност за рециклирање и повторна употреба на биокомпозитите PLA/RH. Кај биокомпозитите произведени од нерециклиран полимер и RH, како и кај оние произведени од рециклираните композитни мате-ријали, анализирани се механичките и термичките својства, кои се споредувани со оние на конвенционалните термопластични композити на база на полипропилен (PP), зајакнат со истото полнило. Термичката стабилност на биокомпозитите од рециклирана PLA матрица, како и на оние произведени од рециклиран композит, е практично непроменета. Внесувањето на рециклирана матрица во биокомпозитите резултира во намалување на модулот и јачината на свиткување за околу 50 %. Искористувањето на смесите добиени по термо-механичкото рециклирање на целиот V. Srebrenkoska, G. Bogoeva-Gaceva, D. Dimeski Maced. J. Chem. Chem. Eng. ...

Abstract:The aim of this work was to determine the fl exural properties of hybrid composites parts cut from trapezoidal core made of carbon/glass fi bers impregnated in epoxy resin with help of fi lament winding technology. Values for stress, strain and module of elasticity were calculated using three point bending test. The tests were performed according to American Society for Testing and Materials (ASTM) standards. Hybrid fi ber reinforced plastic (FRP) laminates exhibit progressive failure consisting of fi ber failure, debonding, and delamination.Further, the paper investigates the content of voids inside the structure, the interface fi ber/epoxy resin using scanning electron microscope and the procedures involved in the laminate design, fabrication, experiments and analysis of composite part for decks.