Introduction
Natural rubber play more important role in the industry due to its excellent physical properties in terms of high
mechanical strength, low heat build up, excellent flexibility and resistance to impact and tear. However, NR has some
drawbacks, for instance, low heat resistance, sensitive to chemicals and solvent. One route to improve heat resistance
properties of NR is chemical modification by incorporating phosphorus containing moieties (Derouet
et al
, 2001).
Thermoplastic elastomer (TPEs) are materials that well-known and make benefit in a broad industries due to
processing behavior of thermoplastic but having the mechanical properties and elastic recovery similar to the
conventional vulcanized rubber (N.R. Legge
et al
, 1987). Thermoplastic vulcanizate (TPV) or dynamic vulcanized (DV)
is a class of TPE based on rubber and thermoplastic compositions where the rubber phase is dynamically vulcanized.
In this work phosphate groups were incorporated onto NR molecules with the aim to improve heat resistant
properties. The modified product was then used as a blend component to blend with polypropylene. This was aimed to
prepare thermoplastic elastomer material with high heat resistant properties. Furthermore, effect of vulcanization systems
(i.e., sulphur, peroxide, phenolic resin and mixed sulphur/peroxide) on properties of the TPVs were investigated on
mechanical and dynamic properties.
Materials & methods
Materials
Epoxidized natural rubber with 25 mol% of epoxide groups (ENR-25) used as a blend component,
manufactured by Muang Mai Guthrie, Surat Thani, Thailand. An injection-molding grade (P700J) with MFI of 12
g/10min at 230
o
C and specific gravity of 0.91 used as a thermoplastic blend component, manufactured by the Thai
Polypropylene Co., Ltd., Royong Thailand. Hydroxymethylol phenolic resin (HRJ-10518) used to prepare phenolic
modified polypropylene (PhHRJ-PP) compatibilizer was manufactured by Schenectady International Inc, Freeport, USA.
Stannous chloride (SnCl
2
.2H
2
O) used as a catalyst for a preparation of the blend compatibilizer was manufactured by
Ajax Finechem Ltd. (NSW, Australia). Dicumyl peroxide used as a vulcanizing agent was manufactured by Wuzhou
International Co., Ltd., China. Zinc oxide and stearic acid used as an activator were manufactured by Global Chemicals
Co., Ltd., Samutprakarn and Imperial I\ndustries, Co., Ltd, Pathumthani, Thailand, respectively. Sulphur used as a
vulcanizing agent was manufactured by Ajax Finechem Co., Ltd., Samutprakarn, Thailand. MBTS used as an accelerator
was manufactured by Flexsys (USA). Phenol type antioxidant, Wingstay
®
L (Polymeric sterically hindered phenol)
was
manufactured by Eliokem. Inc., USA.
Methods
1. Preparation of DSNR
The ENR was first masticated for 1 min using an internal mixer (a Brabender Plasticorder) at 170
o
C and 60
rpm. The dibutyl phosphate at a concentration of 6 wt % of ENR was then added into the mixing chamber and continued
mixing for 2 min. The chemical structure of DSNR was then characterized by Fourier Transform Infrared
Spectrophotometer, FT-IR)
