The effect of n-BA, HDDA and TMPTMA on chemical and physical properties of ultra-violet vulcanization natural rubber latex / Mohd Noorwadi Mat Lazim

The NR latex formulated with 2 pphr of 2–hydroxy-2-methyl-1-phenylpropanoid
photo-initiator and 3 phr of acrylate monomer (n-BA, HDDA and TMPTMA) was
labelled as NR/n-BA, NR/HDDA and NR/TMPTMA. The formulations were exposed
to UV radiation source from 400W medium pressure mercury lamp at 30, 90, 180 and
300 minutes. The irradiated latex formulations formed into rubber film by using
coagulant dipping method. The rubber films were subjected to testing such as tensile
strength, modulus, swelling, FTIR, TGA, DSC and AFM. The testing was carried out
to study the effect of acrylate monomer and UV irradiation time to NR latex. It was
found that formulation NR/HDDA expose to UV radiation for 180 minutes has the
highest tensile strength, M700 and crosslink density at 13.9 MPa,3.75 MPa and 6.5 x
10-6 mole/g, respectively. The absorption and contact angle test is carried to study the
diffusion and wetting effecting of acrylate monomer to NR. It was found that n-BA has
highest diffusion and wetting effect to NR. NR/HDDA had highest tensile due to HDDA
has 2 functional group in chemical structure contribute to better crosslink efficiency.
The FTIR spectra show that the C=C peak in NR disappear with presence of acrylate
monomer and the appearing of new peak of C=O, ring C-C and vibration aromatic ring
indicate that the acrylate monomer strongly attached to NR. The NR/HDDA
formulation was chosen to study the effect of oxygen on UV vulcanization NR latex.
The NR/HDDA formulation was exposed to UV radiation under inert atmosphere at 90
and 180 minutes. The irradiated NR/HDDA was formed to rubber film and subjected to
tensile, swelling and AFM test. It was found that the tensile and crosslink density of
NR/HDDA film increases when the UV irradiation of NR latex process carried out
under inert atmosphere. The tensile strength of NR/HDDA films expose to UV
irradiation for 3h under inert atmosphere is 20.3 MPa. The surface topology of
formulated NR films show that the reaction of monomer to form crosslink, grafting and
polymer is faster than diffusion of monomer into interior NR latex particles. This
indicates that the vulcanization process only occur at surface of NR latex particles
meanwhile the core of NR latex particles remain unvulcanised.The ability of acrylate
monomer diffuse in particle and number of functional group in acrylate monomer
influence crosslink efficiency. The formation of polyacrylate and grafted polyacrylate
to NR chain increases the physical crosslink in NR contribute to the enhancement of
tensile properties.