Alkali concentrations 1 Caustic soda Fibers 1 Lignocellulosic composition 1 Mechanical behaviour 1 Mechanical behaviours 1 Morphology 1 Oil palm 1 Oil palm stalk fibres (OPSF) 1 Palm oil 1 Pre-Treatment 1 Pre-treatment 1 Scanning electron microscopy 1 Sodium 1 Sodium hydroxide (NaOH) 1 Sodium hydroxides 1 Stress analysis 1 Stress relaxation 1 Stress relaxation tests 1 Unloading 1 Viscoelastic behaviour 1 Viscoelastic modeling 1 Viscoelasticity 1