Nondestructive testing of defects in adhesive joints

potassium ditelluratoargentate (III) redox system. The evidence of grafting was obtained from IR
spectra and gravimetric analysis. Thermal stability, crystallinity, and morphology of the graft
copolymers were also studied [6].
Mwaikambo and Ansell [7] have prepared the hemp fiber reinforced cashew nut shell liquid
composites and reported that tensile strength and modulus of untreated hemp fiber composites
increase with increase in the molding pressure possibly due to reduced porosity. The properties of
alkali treated hemp mat-cashew nut shell liquid composites decrease with increase in the molding
pressure due to the breakage of entangled needle punched hemp fiber bundles, which have also
become stiffer after alkali treatment and the hemp-cashew nut shell liquid interface is more
coherent for the untreated than the alkali treated fiber. Schartel et al [8] have studied the thermal
and fire behaviour of flax fiber reinforced PP composites containing ammonium polyphosphate
and expandable graphite as fire retardants. The fire retardancy is a technical breakthrough for flax
fiber reinforced PP composites.
Kaith et al [9-11] and Kalia et al [12-13] have reported the reinforcement of plastics with graft
copolymers of flax fibers and it has been found that composites reinforced with graft copolymers
of flax fibers showed better mechanical properties in comparison to original flax reinforcement.
Mechanical properties of composites reinforced with acrylate grafted henequen cellulosics fibers
were studied. They found that best results could be obtained with poly(MMA) grafted cellulose
fibers because of better fiber-matrix adhesion [14]. Since the use of graft copolymers as
reinforcing material in the preparation of composites is meagerly reported in literature, so in the
present paper, we report the preparation of phenolic composites using flax-g-poly(MA) as
reinforcing material.
Experimental
Materials
Natural flax fibers (Linum usitatissimum) were supplied by Department of Agronomy, CSK
HP Agriculture University, Palampur (India). Phenolic resin (resole) was prepared by the reaction
of phenol (S D Fine-Chem Ltd., India) and formaldehyde (CDH, India) in material science
laboratory [11].
Flax fibers were Soxhlet extracted with acetone for 72 h. MA (Fluka) was washed with 5%
sodium hydroxide followed by water and was dried over anhydrous sodium sulphate. The dried
monomer was distilled and the middle fraction was used. Libror AEG-220 (Shimadzu make)
electronic balance was used for weighing purpose. Graft Copolymerization of MA onto Flax was
carried out as per method reported earlier [12-13]. IR spectra of the ungrafted and grafted flax
fibers were taken with KBr pellets on PERKIN ELMER RXI Spectrophotometer. Scanning
electron microscopic studies of flax and its graft copolymers were carried-out on Electron
Microscopy Machine (LEO 435 VP). Thermogravimetric analysis and differential thermal
analysis studies were carried-out in air at a heating rate of 10°C/min on a thermal analyzer
(LINSEIS, L-81 11). X-ray diffraction studies were performed on X-ray diffractometer (Bruker
AXS D8 Advance) as per reported methods [15-17].
Composites were prepared in Compression Molding Machine (SANTEC, India). Mechanical
studies such as wear-resistance of the composites were carried-out on Wear & Friction Monitor
(DUCOM, 20LE) and tensile strength, compressive strength, modulus of rupture (MOR),
modulus of elasticity (MOE), and stress at the limit of proportionality (SP) of PF composites were
carried on Universal Testing Machine (HOUNSFIELD, H25KS) [9-13].
Results and Discussion
C2, C3, and C6 hydroxyls and the C-H groups are the active cites for grafting in cellulosics. The
grafting onto flax fibers in presence of FAS-H2O2 as initiator is supposed to take place as per the
mechanism proposed by various authors [18].
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