Abstract
Green composites made of polylactide (PLA) and short flaxseed fibers (FFs) at 20 wt % were successfully compounded by twin-screw extrusion (TSE) and subsequently shaped into pieces by injection molding. The linen waste derived FFs were subjected to an alkalization pretreatment to remove impurities, improve the fiber surface quality, and make the fibers more hydrophobic. The alkali-pretreated FFs successfully reinforced PLA, leading to green composite pieces with higher mechanical strength. However, the pieces also showed lower ductility and toughness and the lignocellulosic fibers easily detached during fracture due to the absence or low interfacial adhesion with the biopolyester matrix. Therefore, four different compatibilization strategies were carried out to enhance the fiber–matrix interfacial adhesion. These routes consisted on the silanization of the alkalized FFs with a glycidyl silane, namely (3-glycidyloxypropyl) trimethoxysilane (GPTMS), and the reactive extrusion (REX) with three compatibilizers, namely a multi-functional epoxy-based styrene-acrylic oligomer (ESAO), a random copolymer of poly(styrene-co-glycidyl methacrylate) (PS-co-GMA), and maleinized linseed oil (MLO). The results showed that all the here-tested compatibilizers improved mechanical strength, ductility, and toughness as well as the thermal stability and thermomechanical properties of the green composite pieces. The highest interfacial adhesion was observed in the green composite pieces containing the silanized fibers. Interestingly, PS-co-GMA and, more intensely, ESAO yielded the pieces with the highest mechanical performance due to the higher reactivity of these additives with both composite components and their chain-extension action, whereas MLO led to the most ductile pieces due to its secondary role as plasticizer for PLA.
Highlights
In the field of polymers technology, one of the most sought and researched objectives nowadays is the replacement of petroleum derived materials with natural and renewable ones
The present study evaluated andorcompared the effect ofgroups surface treatments and different reactive oligomers based on epoxy, maleic, glycidyl methacrylate have successfully compatibilized compatibilizers performance of green composites based on[22,50,51,52]
field emission scanning electron microscopy (FESEM) analysis of the alkali-pretreated flaxseed fibers (FFs) prior and after silanization, respectively, shown in Figure 3b,c, indicated that fiber diameter varied in the 10–25 μm range and it was unaltered during silanization
Summary
In the field of polymers technology, one of the most sought and researched objectives nowadays is the replacement of petroleum derived materials with natural and renewable ones. It is widely known that polymer composites based on lignocellulosic particles or fibers habitually present low mechanical and thermomechanical performances due to the absence or poor interfacial adhesion between the fillers and the matrix This issue has been ascribed to the difference in hydrophobicity between the polymers and the plant derived fillers [38,39,40]. Among the different modification of the natural fillers can influence some characteristics such as their fiber surface pretreatments based on chemical substances, alkalization, called “mercerization”, is hydrophobicity and porosity [43] These methods are generally based on cleaning and/or activating the most standardized one due to it reduces and increases effectiveness the filler surface and they include both thehydrophilicity use of chemicals and physical methods Thermomechanical properties of the injection-molded green composite pieces were analyzed and related to the different compatibilization strategies explored
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