6. PROCESS FLOW As of now, there is no standard procedure to mix the blend that we ought to make. Hence we make two assumptions out of which one with superior qualities would be screened and selected. Based on proper analysis of the trial and error leads to an optimum solution. 6.1 ALTERNATIVE 1 Figure (viii): Process Alternative 1 Step 1: FKM + EPDM-g-MAH Step 2: Addition of UHMWPE Step 3: Final Blend The compatibilizer EPDM-g-MAH is first reactively mixed with the fluoroelastomer and then this preblend is mixed with subsequent addition of UHMWPE. Proper cross mixing, dispersion and homogeneous distribution of the various phases yields the final blend. 6.2 ALTERNATIVE 2 Figure (ix): Process Alternative 2 Step 1: UHMWPE + EPDM-g-MAH Step 2: Addition of FKM Step 3: Final Blend The compatibilizer EPDM-g-MAH is first reactively mixed with UHMWPE and then this preblend is mixed with subsequent addition of the appropriate grade of fluoroelastomer. Proper cross mixing, dispersion and homogeneous distribution of the various phases yields the final blend. 8. DESCRIPTION OF VARIOUS TRIALS CONDUCTED 8.1 TRIAL 1 (WITH NO COMPATIBILIZER) The blend of the two polymers namely, FKM and UHMWPE was done on the first trial using no compatibilizing agent. Hence the ratio of the polymers was fixed to 80:20 ratios. Table 3: Formulation for Trial 1 Polymer Ratio FKM 80 UHMWPE 20 The polymers seemed as if it was mixing quite well on a 2-roll mill. The mixing temperature was adjusted to nearly 130?C. This was done in order that the UHMWPE powder may melt on the mill and thereby mix with the rubber. This found to serve the purpose initially. But this led to thermal degradation of the FKM matrix leading to embrittlement in the sample. Also as there was no compatibilizer added to blend both the rubber phase and the plastic phase he, the crystals of UHMWPE started to reappear on the surface of the sample. This occurred after the compound was removed from the mill and allowed to stay at room temperature. The chief reason for such behaviour may be because the UHMWPE powder was unable to penetrate into the matrix of the rubber. Rather than being penetrated into the matrix, the plastic material was just coated over the rubber. Hence, phase separation occurred. Figure (xiv): 80:20 Ratio sample mixed without compatibilizer and compressed 8.1.1 Possible Reasons of Error Polarity difference between both polymers was not balanced by addition of a compatibilizing agent. High mixing temperature leading to thermal degradation of FKM. 8.2 TRIAL 2 (WITH MAH AS COMPATIBILIZER) In the second trial an acidic reagent, Maleic anhydride (MAH) was added into the blend of FKM and UHMWPE. The acidic reagent was assumed to enter the blending media as a compatibilizing agent. It would break the stable bonds of the FKM matrix thereby leading to possibility of a reactive site which would then bond to UHMWPE. An amine cure system has been introduced into the formulation viz. Diak 1. The chemical name of Diak 1 is (6 aminohexyl) carbamic acid. Along with this the amine cure system also involves inclusion of a coagent system which is a mixture of Magnesium oxide and Calcium hydroxide. Table 4: Formulation for Trial 2 Polymer Ratio FKM 80 UHMWPE 20 MAH 10 Diak 1 2 MgO 3 Ca(OH)2 6 As the theory stated everything went well in the mixing stage at a temperature of 30?C. But the blended sample was unable to cure even after compression moulding for 20 min at 175?C. Figure (xv): Cure hindered in Trial 2 8.2.1 Possible Reasons of Error Acidity of MAH may have led to retarding effect on the sample. Decomposition of MAH liberated gas and made a porous structure after curing. This led to breakage of the connecting link between the two polymers and hence the blend was distorted. Crystallization of UHMWPE after returning back to room temperature post curing lead to less significant interbonding. 8.3 TRIAL 3 (WITH EPDM & MAH AS COMPATIBILIZER) In the third trial an acidic reagent, Maleic anhydride (MAH) was added into the blend of FKM and UHMWPE in the presence of a third polymer namely, Ethylene Propylene Diene Rubber (EPDM) as a base. The acidic reagent was assumed to enter the blending media as a compatibilizing agent. It would break the stable bonds of the FKM matrix thereby leading to possibility of a reactive site which would then bond to UHMWPE. All these reactions would occur with EPDM as a base as both polymers are compatible with it. With the introduction of EPDM into the stock, amine based curatives would not be sufficient enough to cure them. Hence in this case a peroxide DCP 98 has been added i.e. Dicumyl peroxide with 98% active peroxide content. Another important addition is that of TAIC i.e. Triallyl isocyanurate, which is used a necessary coagent whenever FKM has to be cured with peroxide. Table 5: Formulation for Trial 3 Polymer Ratio FKM 55 EPDM 35 UHMWPE 10 MAH 2 DCP 98 2.75 TAIC 0.7 Once again the polymer mixed well and this time the curing was also carried out completely without any sort of hindrance. A cured sheet was made at 180?C for 15 minutes and the sample was found to be suitable for Scanning Electron Miscroscopy (SEM). But the issue here was that the physical and mechanical strength of the cured sample was very less. Figure (xvi): Cured Sample without hinderance in Trial 3 8.3.1 Possible Reasons of Error The physical and mechanical strength of the cured sample was found to be less as there was no filler added so far into the compound. Secondly, there is a possibility that the FKM phase may have been uncured by the used peroxide. 8.4 TRIAL 4 (WITH 5% EPDM-g-MAH AS COMPATIBILIZER) Prior to the fourth trial, a compatibilizer was developed in house for the blending of FKM with UHMWPE. The steps involved in the grafting of maleic anhydride (MAH) on to EPDM has been explained in Chapter 9. Instead of using both MAH and EPDM separately as a connecting link here the prior has been grafted on to the latter. This provides a bridge type network structure with bipolar heads with the polar MAH head reacting with the FKM phase and the non polar EPDM head reacting with the UHMWPE phase. Table 6: Formulation for Trial 4 Polymer Ratio FKM 55 EPDM 30 EPDM-g-MAH 5 UHMWPE 10 DCP 98 2.75 TAIC 0.7 CaCO3 6 Calcium carbonate has been added as a binder in order to bind the EPDM phase with other base polymers. The mixing was carried out on Brabender Plasticorder at 130?C. A sheet was cured at 170?C for 15 minutes. Figure (xvii): Cured Sample in Trial 4 8.5 TRIAL 5 (WITH 10% EPDM-g-MAH AS COMPATIBILIZER) The fifth trial was carried out exactly similar to that of the last trial. The only difference was that the dosage of the lab made compatibilizer, EPDM-g-MAH was raised to 10%. All remaining compounding, mixing and processing were replicated. Table 7: Formulation for Trial 5 Polymer Ratio FKM 55 EPDM 25 EPDM-g-MAH 10 UHMWPE 10 DCP 98 2.75 TAIC 0.7 CaCO3 6 It was observed that increasing the dosage of compatibilizer improved the consistency of the mix. Figure (xviii): Cured Sample in Trial 5 9. MANUFACTURE OF EPDM-g-MAH 9.1 STEPS INVOLVED Dissolution of EPDM. Breaking molecular chains of EPDM using a peroxide reagent. Addition of MAH in liquid form with simultaneous vigorous stirring. Extraction of unreacted substituents. Final leaching and drying. Solution mixing is carried out at elevated temperatures, preferably at 80?C. The estimated time of preparation is of 3 days.
10. SCANNING ELECTRON MICROSCOPY (SEM)
A small sample of the dimensions 2cm ? 2cm ? 0.3 cm is cut from a cured sheet. The sample is first and foremost plated with gold in order to make it conductive to the transmitting microscopic waves. Then the gold plated sample is kept in the SEM machine and zoomed across the surface in order to study morphology. The images obtained from SEM suggested that some amount of improper blending still exists, after Trial 3, in the mass. But overall more than 70% of the blending was effected. Even better blend was obtained in the subsequent trials.
This dissertation took off and terminates at the concept that durability of pharmaceutical hoses carrying concentrated acids shall be improved by blending FKM with UHMWPE. The above attached testing reports clearly states that the blending improves subsequent properties. FKM imparts the required resistance against the various chemicals and other hazardous atmosphere. Whereas, UHMWPE improves the flow in hose due to its low friction property along with chemical resistance. An addition of a third polymer viz. EPDM has been added as a base in which the blending occurs using the laboratory made compatibilizer EPDM-g-MAH.