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Abstract:
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In the first part of the study we probed the effectiveness of rice bran oil as a
multipurpose compounding ingredient for nitrile (NBR) and chloroprene (CR) rubbers.
This oil has already been successfully employed in the compounding of NR and SBR in this laboratory.In this context we thought it worthwhile to try this oil in the polar
rubbers viz, NBR and CR also. The principle of like dissolves like as applicable to solvents
is equally applicable while selecting a plasticiser, elastomer combination. Because of the
compatibility considerations polar plasticisers are preferred for polar rubbers like NBR and
CR. Although plasticisation is a physical phenomenon and no chemical reaction is
involved, the chemical structure of plasticisers determines how much physical attraction
there is between the rubber and the plasticiser. In this context it is interesting to note that
the various fatty acids present in rice bran oil have a long paraffinic chain, characteristic of
waxes, with an acid group at the end of the molecule. The paraffinic end of the molecule
contributes lubricating effects and limits compatibility whereas the acid end group
contributes some polarity and is also chemically reactive. Because of absorption of acid
group on the surface of pigments, these acids will have active pigment wetting
characteristics also. These factors justifies the role of rice bran oil as a co-activator and
lubricating agent for NBR and CR. In fact in our study we successfully replaced stearic
acid as co-activator and aromatic oillDOP as processing aid for CR and NBR with rice
bran oil.This part of the study has got special significance in the fact that rubber
industry now heavily depends on petroleum industry for process oils. The conventional
process oils like aromatic, naphthenic and paraffinic oils are increasingly becoming
costlier, as its resources in nature are fast depleting. Moreover aromatic process oils are
reported to be carcinogenic because of the presence of higher levels of polycyclic aromatic
compounds in these oils.As a result of these factors, a great amount research is going on world over for newer processing aids which are cost effective, nontoxic and performanance
wise at par with the conventional ones used in the rubber industry. Trials with vegetable
oils in this direction is worth trying.Antioxidants are usually added to the rubber compound to minimise ageing
effects from heat, light, oxygen etc. As rice bran oil contains significant amount of
tocopherols and oryzanol which are natural antioxidants, we replaced a phenolic
antioxidant like styrenated phenol (SP) from the compound recipe of both the rubbers with
RBO and ascertained whether this oil could function in the role of antioxidant as well.Preparation and use of epoxidised rice bran oil as plasticiser has already
been reported.The crude rice bran oil having an iodine value of 92 was epoxidised in
this laboratory using peracetic acid in presence of sulphuric acid as catalyst. The epoxy
content of the epoxidised oil was determined volumetrically by treating a known weight of
the oil with excess HCI and back titrating the residual HCI with standard alkali solution.
The epoxidised oil having an epoxy content of 3.4% was tried in the compounding of NBR
and CR as processing aids. And results of these investigations are also included in this
chapter. In the second part of the study we tried how RBO/ERBO could perform when
used as a processing aid in place of aromatic oil in the compounding of black filled NRCR
blends. Elastomers cannot have all the properties required for a particular applications,
so it is common practice in rubber industry to blend two elastomers to have desired
property for the resulting blend.In this RBO/ERBO was tried as a processing aid for
plasticisation, dispersion of fillers, and vulcanisation of black filled NR-CR blends.Aromatic oil was used as a control. The results of our study indicate that these oils could
function as a processing aid and when added together with carbon black function as a cure
accelerator also.PVC is compatible with nitrile rubber in all proportions, provided NBR has
an acrylonitrile content of 25 to 40%. Lower or higher ACN content in NBR makes it
incompatible with PVC.PVC is usually blended with NBR at high temperatures. In order
to reduce torque during mixing, additional amounts of plasticisers like DOP are added. The
plasticiser should be compatible both with PVC and NBR so as to get a homogeneous
blend. Epoxidised soyaben oil is reported to have been used in the compounding of PVC as
it can perfonn both as an efficient plasticiser and heat stabilizer.At present DOP
constitute the largest consumed plasticiser in the PVC compounding. The migration of this
plasticiser from food packaging materials made of PVC poses great health hazards as this
is harmful to human body. In such a scenario we also thought it worthwhile to see whether
DOP could be replaced by rice bran oil in the compounding of NBR-PVC blends
Different blends of NBR-PVC were prepared with RBO and were vulcanized using
sulphur and conventional accelerators. The various physical and mechanical properties of
the vulcanisates were evaluated and compared with those prepared with DOP as the control
plasticiser. Epoxidised rice bran oil was also tried as plasticiser for the preparation of
NBR-PVC blends. A comparison of the processability and cure characteristics of the
different blends prepared with DOP and ERBO showed that ERBO based blends have
better processability and lower cure time values. However the elastographic maximum
torque values are higher for the DOP based blends. Almost all of the physical properties evaluated are found to be slightly better for the DOP based blends over the ERBO based
ones. However a notable feature of the ERBO based blends is the better percentage
retention of elongation at break values after ageing over the DOP based blends. The results
of these studies using rice bran oil and its epoxidised variety indicated that they could be
used as efficient plasticisers in place of DOP and justifies their role as novel, nontoxic, and
cheap plasticisers for NBR-PVC blends. |