Analysing The Processes For Mixing Rubber Biology Essay

Normally the “ formula ” for a gum elastic compound is given in footings of phr ( parts per hundred gum elastics by weight ) . The existent weights used are calculated from the densenesss of the ingredients, the mixing chamber volume and the fill factor.

The fill factor is the fraction of the mixing chamber volume occupied by the compound during blending. Given that the blending chamber has a volume of 1.5litres and a fill factor of 0.74 was used, demo how the weights given in the tabular array can be calculated from the phr values and densenesss.For computations of the weight that should be used in the preparation, the volume of the constituents has to be determined. This is presuming that phr = mass.

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Where, I? = Density ( kg/m3 ) , M = Mass ( kilogram ) , V = Volume ( M3 )MaterialsphrDensity ( kg/m3 )Styrene Butadiene Rubber ( SBR )100920Zinc Oxide ( ZnO )55600Stearic Acid1850Carbon Black ( N330 )401800Antidegradants ( AO )11000Sulfur12100N- Cyclohexyl-2-benzothiazolesulphenamide ( CBS )1.51000Tetramethylthiuramdisulphide ( TMTD )0.51000SBR:ZnO:Stearic Acid:Carbon Black:Antidegradant ( AO ) :Sulfur:N- Cyclohexyl-2-benzothiazolesulphenamide ( CBS ) :Tetramethylthiuramdisulphide ( TMTD ) :Entire Volume:The following measure would be to cipher the per centum by weight that the constituents take up in the chamber:SBR:

=

=

ZnO:

=

=

Stearic Acid:

=

=

Carbon Black:

=

=

Antidegradant ( AO ) :

=

=

Sulfur:

=

=

N- Cyclohexyl-2-benzothiazolesulphenamide ( CBS ) :

=

=

Tetramethylthiuramdisulphide ( TMTD ) :

=

=

With the per centum by weight of each constituent calculated, we can so cipher the existent volume that each constituent takes up:SBR:

=

=

ZnO:

=

=

Stearic Acid:

=

=

Carbon Black:

=

=

Antidegradant ( AO ) :

=

=

Sulfur:

= =

N- Cyclohexyl-2-benzothiazolesulphenamide ( CBS ) :

=

=

Tetramethylthiuramdisulphide ( TMTD ) :

=

=

Weight of the single additives constituent can so be recalculated utilizing the existent volume and denseness:SBR:

=

=

ZnO:

=

=

Stearic Acid:

=

=

Carbon Black:

=

=

Antidegradant ( AO ) :

=

=

Sulfur:

=

=

N- Cyclohexyl-2-benzothiazolesulphenamide ( CBS ) :

=

=

Tetramethylthiuramdisulphide ( TMTD ) :

=

=

Table 2: SBR Formulation for Compounding and its weightMaterialsphrDensity ( kg/m3 )Percentage ( % )Vol ( M3 )Act.

Volume ( M3 )Weight ( g )Styrene Butadiene Rubber ( SBR )10092079.670.1080.884 X 10-3813.

28Zinc Oxide ( ZnO )556000.6580.893 X 10-30.

0073 X 10-340.88Stearic Acid18500.8671.176 X 10-30.00962 X 10-38.

18Carbon Black ( N330 )40180016.230.0220.18 X 10-3324Antidegradants ( AO )110000.

7380.0010.008 X 10-38Sulfur121000.3510.476 X 10-30.003896 X 10-38.

17N- Cyclohexyl-2-benzothiazolesulphenamide ( CBS )1.510001.1060.

00150.01227 X 10-312.27Tetramethylthiuramdisulphide ( TMTD )0.510000.3680.

00050.00408 X 10-34.08Question 2:Determine the sum of pulverization lost during commixture and show it as a per centum of the batch weight

=

=

=

= 1.10 %

=

=

= 2.80 %It was observed from the experiment the weight loss of the compounded merchandise. Compound 1 ( 20 mins mixing clip ) was observed to hold a lower weight loss as compared to intensify 2 ( 4 mins mixing clip ) .

In gum elastic commixture, there would be a few mechanism of blending taking topographic point at the same clip. They are chew, scattering, distribution and incorporation [ 1 ] . However without sing the effects of clip on commixture, it was observed for some additives, pulverization signifiers were used.

The use of pulverization itself may hold resulted in some weight loss. Residue of the pulverizations was observed on the container used to weigh the sample itself. Besides, the pulverizations were poured into the sociable utilizing a hopper. This may besides ensue in some loss of pulverization by the action of pouring. While the sum of pulverization used was really small in this experiment, the possibility of a pulverization “ cloud ” organizing above the hopper was possible.

The use of pulverization was likely the ground why there was some weight loss in compound 1, or even a sample that could be “ absolutely assorted ” .As mentioned earlier, pulverizations signifiers of the additives were used and the apprehension of pulverization and the mechanism of blending will help in the understanding weight loss difference between compound 1 and 2. Powderize itself will agglomerate and certain forces will be required to interrupt them down.( 1 ) Incorporation plants by distortion of the gum elastic, ensuing in an increased surface country for accepting the linear atoms. Relaxation of the gum elastic would so encapsulate the atom within the gum elastic matrix. The gum elastic would so breakdown into smaller pieces and mix with the atoms and re-coalescence seals it in the gum elastic matrix. By cut downing the commixture clip, some of the pulverization might still be in an agglomerative signifier that could be on the surface or within the matrix. The effect was that the during remotion of the compound from the mold, compound 2 with significantly lower commixture clip will ensue in more weight loss by the pulverizations.

( 2 ) Distribution was besides known as “ simple commixture ” where it will increase the entropy of the atoms within the gum elastic matrix with no alterations in size of the atoms. Blending clip in this instance would hold small or no consequence as the longer the commixture clip, the higher the chance the mixture can be more random. However this does non bespeak that there will be any alterations in pulverization loss as a map of clip.( 3 ) Chew will change the rheological belongingss of the elastomer. Two sub mechanism of chew were in topographic point ; ( I ) mechano-chemical as a consequence of shear emphasis, ( two ) thermo-oxidative which was due to the oxidative concatenation scission reaction in the presence of O in elevated temperature.( 4 ) Dispersive commixture will cut down the pulverization agglomerate to its sum. With lesser commixture clip, the atoms will be more in the agglomerative signifier and ensuing in higher weight loss when removed.The combination of the commixture mechanism will bespeak the ground of higher weight loss from deficient commixture clip.

The distributive and diffusing commixture mechanism works together to let the pulverization atoms to be good dispersed and distributed in the gum elastic matrix. Longer chew clip will let a gum elastic with lower viscousness to be produced, leting better efficiency of the incorporation, diffusing and distributive commixture mechanisms to happen.Sum uping on the points, the pulverizations loss in compound 1 should be due to managing of pulverization whereas in compound 2, it is a combination of deficient commixture and pulverization handling.Question 3:Describe and briefly remark on the visual aspect of the two compounds in relation to the commixture conditions.Table 3: Observations of gum elastic compounded with different commixture clipBlending Time ( mins )

A

420Observations* Dull/matte Surface* Glossy Surface* Less Elastic* More Elastic* Rough Surface* Smooth Surface* Loses stuff when* No loss of stuffs whenstretched/touchedstretched/touched

A

A

* Harder* SofterAs discussed earlier, the mechanism of commixtures were chew, incorporation, distribution and scattering.

The differences spotted in Table 2 could likely be the consequences of either a individual commixture mechanism or a interactive consequence of the different mechanisms.The consequence of deficient commixture clip could ensue in a gum elastic compound that in which the viscousness was still really high, therefore cut downing the effectivity of distributive, diffusing and incorporative mechanisms. With a reduction in those mechanisms, pulverization might still stay in the matrix or on the surface as agglomerates, ensuing in rough and matte surface coating. Insufficient commixture clip besides consequences in lesser incorporation of the additives into the gum elastic matrix, doing it to lose stuffs when stretched or touched.However it should besides be noted that longer does non intend better gum elastic. Where the grade of commixture is higher, long commixture clip might ensue in a gum elastic compound with a lower mechanical belongings or unsuitable remedy belongings for the application. Blending clip should be controlled at a suited clip where the compound can be sufficiently assorted and yet still give suited gum elastic compounds with appropriate rheological belongingss for the hardening procedure.Question 4:Plot batch temperature against blending clip for both compounds.

On the temperature profile indicate when additives were added.Addition of staying additivesAddition of SBR and Carbon BlackGraph 1. Plot of Temperature against blending clip for both compoundsFrom Graph 1, we can detect the temperature profile for both compounds during the commixture procedure. In compound 1, the balance of the additives were added at T+15min and compound 2 at T+2min.The temperature bead occurs at the clip where the additives were added. During commixture, shear forces will do the gum elastic to hold a heat construct up and when because gum elastic does non possesses good heat dissipation belongingss, the heat will go on to construct up.

When the additives were added, the temperature drops due to the debut of air and besides the pulverizations where was at room temperature. The atoms could likely move as a heat sink to take some heat off from the gum elastic and ensuing in a little bead. In compound 2, which was compounded instantly after compound 1, the rate of heat build up was faster, likely due to the residuary heat from the chamber that lead to the faster heat construct up.Question 5:Suggest how you can alter the commixture conditions to better quality of the compound.There are many variables that can be optimized to accomplish a better quality compound, listed but non limited to:( 1 ) Rotor Speed- High rotor velocity will ensue in the development of heat. Heat in gum elastic chew was non desired as it will ensue in the extra thermo-oxidative chew which is the concatenation scission of gum elastic concatenation in the presence of O at elevated temperature. Lower rotor velocity can be used to accomplish a better quality.( 2 ) Mix time- Long commixture clip may intend higher mechano-chemical chew via application of shear emphasis.

However, this should be kept at a suited clip whereby the gum elastic achieves the coveted rheological belongingss for the hardening procedure. An accommodation in blending clip may give a better quality merchandise.( 3 ) Chamber temperature- Temperature of the gum elastic is of import. As discussed earlier about the thermo-oxidative chew of gum elastic. An elevated temperature will impact the rheological belongingss of the gum elastic and finally the mechanical belongingss as good. Lower chamber temperature is recommended for better quality merchandises.( 4 ) Circulatory Cooling- As mentioned earlier, a lower temperature is desired in gum elastic commixture. Therefore the add-on of circulatory chilling to the blending chamber will maintain the gum elastic temperature low and hence increasing the quality of the gum elastic compound.

( 5 ) Ram Pressure- Higher random-access memory force per unit area will ensue in a better distributive and diffusing commixture of the gum elastic compound. High force per unit area is by and large desired for commixture, particularly for high viscousness mixes as it will let the decrease of nothingnesss and at the same clip increasing shear emphasis by decrease of slippage. However, it was discovered that a high random-access memory force per unit area at the ulterior phase of commixture, at the point whereby the viscousness of the gum elastic alterations, a high random-access memory force per unit area will hinder with stuff flow within the mixing chamber.

Switch overing the ram force per unit area at suited points will let better quality gum elastic compound.( 6 ) Fill factor- For good commixture, it was believed that the formation of nothingnesss behind the rotor tip and the attendant turbulent flow was necessary. Therefore, the chamber should non be overloaded but yet at the same clip, sufficient stuffs need to be present to let effectual random-access memory force per unit area. If the chamber was overloaded, it is believed that higher commixture clip are required to counterbalance for the consequence. Therefore an optimal fill factor should be used as recommended by the maker for production of better quality gum elastic compounds.( 7 ) Sequence of add-on of additives- There are two methods of blending available, conventional commixture and inverted commixture. Conventional commixture involved the add-on of elastomer foremost for chew before add-on of dry ingredients followed by oils.

Upside down blending mixes all other ingredients except the elastomer foremost, followed by the elastomer. The 2nd method is a fast method and is effectual for compounds with big sum of liquid and big atom size fillers. In our instance, it was noted that the gum elastic and C black was added together foremost. The add-on of C black at a ulterior phase will let better commixture after chew of the gum elastic and besides cut down the temperature somewhat. This would likely increase the quality of the gum elastic compounds.

( 8 ) Type of rotor/mixer-the type of rotor blade will impact the nothingness zone and besides the country of commixture. A suited rotor should be used to accomplish a good quality rubber compound.Session 2 ( Rubber Characterisation )Question 1:Tabulate Mooney Viscosity and Monsanto Curemeter consequences.

Table 3: Mooney Viscosity and Monsanto consequences for Compound 1 and 2

A

A

Compound 1 ( 150oC )Compound 2 ( 150oC )Compound 2 ( 160oC )Compound 2 ( 170oC )Mooney Viscosity ( MU ) ( 1+4,100oC )129676767Minimum Torque ( ML ) ( dNm )23.816.6714.2815.

15Maximal Torque ( MH ) ( dNm )140.48104.76102.3898.49Scorch clip ( ts2 ) ( min )3.

135.133.522.33Remedy clip ( t95 ) ( min )15.1313.868.975.

5Remedy Rate Index ( CRI ) ( min-1 )8.3311.4518.3431.55dM/dt ( dNm/min )8828.

5738.149.22Type of curve

A

MarchingMarchingMarchingEquilibriumQuestion 2:Describe and suggest grounds for the consequence ( or deficiency of consequence ) of blending conditions on the norm and spread of Mooney Viscosity values.Question 3:Viscosity and remedy rate are known to fulfill an Arrhenius-type relation P=Ae-B/T, where P is the belongings being studied, T is absolute temperature for A and B are invariables. Check the cogency of this attack for the singe clip informations which you have obtained. Estimate the maximal safe processing clip for the compound at 100oC. Estimate how long it would be safe to hive away the assorted compound before farther processing.

The given Arrhenius equation:It can be converted to:Table 4: Remedy temperature and scorch clip of compound 2Remedy Temperature ( A°C )150160170Scorch clip ( ts2 ) ( min )5.133.522.331/T ( K-1 )0.

002360.002310.00226ln ( ts2 )

A

1.635111.258460.

84587Graph 2. Plot of ln ( ts2 ) against 1/TFrom the graph:A=1.34 X 10-7B=7390.

81For storage at 23A°C,For storage at 100A°CQuestion 4:Compare the remedy rate indices you calculated at different temperatures utilizing the theoretical look with the dM/dt values you measured straight from the same rheometer hints. Is at that place any tendency between these consequences? Explain your reply.dM/dtCRIGraph 3. Comparison of CRI and dM/dt against temperatureRemedy rate index ( CRI ) was calculated by the undermentioned equation:Where t95 is the remedy clip ( terminal of bring arounding ) , ts2 is scorch clip ( Onset of bring arounding ) .A higher CRI value will bespeak a higher remedy rate and in Graph 3, higher temperature will ensue in a higher CRI.

However from 160A°C to 170A°C, the rate of remedy increased.The other method, dM/dt, is a measuring of torque per unit clip. As gum elastic remedies, more crosslinking will happen and higher torsion values will be detected.

From Graph 3, the values increased linearly with temperature. Remedy rate is expected to increase with temperature as at higher temperature, more energy was input into the gum elastic compound of the same thickness. Besides as the trial article is a comparatively thin sample, good thermic diffusion was expected and it will be able to absorb the thermic energy more efficaciously, hence ensuing in higher remedy rate with higher temperature.However comparing the two techniques, the inquiry of which method would be more dependable comes to the head. CRI takes into consideration the remedy rate from singe clip till cure clip.

However dM/dt merely considers the steepest portion of the remedy, which was a representation of the remedy rate at upper limit. When a engineer is sing the dependability of both, CRI would likely be more dependable as it takes a wider scope into consideration, which is in between singe clip and remedy clip.Question 5:Describe and suggest grounds for differences or similarities in the curemeter consequences of the compounds you tested.Comparing both curemeter consequences obtained for compound 1 and 2 at 150A°C, the torsion value for compound 1 was higher than compound 2. Reason being was because that compound 1 has a higher mixing clip of 20 mins as comparison to intensify 2 which has a mixing clip of 4 mins. A higher commixture clip will take to more chew, take downing the viscousness by damaging the gum elastic concatenation by mechanical shear emphasis. A longer mixing clip was besides noted to ensue in more heat buildup in the gum elastic and as gum elastic does non possesses good heat dissipation belongingss, the heat will ensue in a thermo-oxidative debasement of the gum elastic, ensuing in an even lower viscousness.

The scorch clip of compound 2 was higher than compound 1, which could be a consequence of more uniformed dispersive, distributive and incorporative commixture. Additives were good assorted in this instance and leting most significantly the crosslinking agents and gas pedals to be good assorted. This allow a shorter singe clip and shorter optimal remedy clip in this instance.

For compound 2, the maximal torsion values were found to be diminishing with higher temperature. It should be noted that during the measuring of the torsion values, an hovering phonograph record was invariably traveling and damaging the gum elastic ironss. An increased temperature will further worsen the consequence by thermo-oxidative debasement. Besides higher temperature will take to higher concatenation mobility and besides lower viscousness, hence diminishing the maximal torsion with higher trial temperature. At higher temperature, lower singe clip and optimal remedy clip was observed. This is because the gum elastic trial article is a comparatively thin article and it will let effectual heat transportation.

A higher temperature hence reduces the singe clip, optimal remedy clip and at the same clip cut downing the CRI and dM/dt.Question 6:From your consequences, suggest the general consequence of blending clip on down-stream processing of the compound used in these experiments.Longer mixing clip will ensue in lower viscousness due to the 2 effects of chew ; ( 1 ) the mechano-chemical consequence of concatenation breakage by the applied shear emphasis and ( 2 ) thermo-oxidative concatenation scission in the presence of heat and O. Long mixing clip will ensue in heat buildup and consequence in the 2nd consequence being more prominent. However the viscousness of the gum elastic should non be excessively high as it can be tough to treat or even damage the machines. The mixing clip should be at an optimal degree that allows good commixture of additives into the gum elastic matrix to let good mechanical belongingss and unvarying remedy. It should non be excessively long to cut down the viscousness or excessively short to do it hard to treat.

It should be controlled at a suited scope for the coveted mechanical and remedy belongingss for the application.Mentions:[ 1 ] Dr. Ali Ansarifar: Handouts of Rheology and Mixing ( MPP217 )[ 2 ] J.L.White, Rubber Processing: Technology, Materials and Principles, Hanser Publishers, New York, 1996.[ 3 ] Freakley P.K.

, Rubber Processing and Production Organization, Plenum New York,1995[ 4 ] Kenny T.N. ( 1995 ) Thesis: Control and Optimisation of Rubber Mixing in an Internal Mixer Loughborough: Loughborough University of Technology

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