Sensivity to moisture and its effect on mechanical behavior of bio-based resins reinforced with cellulosic fibers

SENSITIVITY TO MOISTURE AND ITS EFFECT ON MECHANICAL BEHAVIOR OF BIO-BASED RESINS

REINFORCED WITH CELLULOSIC FIBERS

Newsha Doroudgarian, Liva Pupure and Roberts Joffe

Division of Materials Science

Lulea University of Technology, Lulea, Sweden

*Roberts.Joffe@ltu.se, +46 920 49 19 40, +46 920 49 13 99

In recent years there has been significant development in commercialization of thermoset resins with bio-based content. These resins can be reinforced with cellulosic fibers obtained from plants (e.g. flax, hemp, wood), thus creating entirely bio-based composites. These bio-based constituents (i.e. fibers and resins) as well as their composites exhibit fairly high mechanical properties at ambient conditions. However, if exposed to elevated humidity these materials absorb moisture and their mechanical properties (namely strength and stiffness) might drastically degrade. Therefore, behavior of bio-based composites at different humidity levels should be studied and mechanisms occurring in material must be identified and clearly understood. This study is a part of the development of high performance bio-based composites with improved durability for use at elevated humidity and/or temperature. Composites with different combinations of bio-based resins and cellulosic fibers were manufactured then conditioned at different humidity levels and extensive mechanical characterization was carried out. Microstructure of the materials was investigated through optical and scanning electron microscopy. In order to reduce the water absorption, cellulosic reinforcement was subjected to alkaline and silane chemical treatments prior to manufacturing of composites. Moisture absorption data indicated lower water uptake in fiber treated composites. However, results showed that there might be disturbances in microstructure of composites with fiber treatment, see Figure 1.

Figure 1. SEM images of fracture surfaces, bio-based polymer reinforced by (a) untreated flax fibers, and (b) flax fibers treated with alkaline.

The glass fiber/epoxy composite was chosen as a reference material to which properties of bio-based composites were compared. This comparison showed that some of the bio- based materials exhibit mechanical properties comparable with properties of composites with epoxy matrix, even at elevated humidity.

a b