carbonato exp

34

Babalola and Erhievuyere-Dominic / Innovations in Science and Engineering 2 (2012) 34-40

A Comparative Analysis of The Effects of Calcium Carbonate and Dolomite as Fillers in Polyether Polyurethane Foam Production

Polyether polyurethane foams have completely replaced the old polyester foam due to flexibility, ease of production, quality and economics. Fillers are added to polyurethane foam in order to reduce cost and provide some desired structural and mechanical properties. In this work, the effects of calcium car-bonate (calcite – CaCo3) and dolomite [CaMg(Co3)2] as fillers on the struc-tural and mechanical properties of foam are investigated. For calcium carbon-ate as filler, all properties tested are approximately maximized at 10% con-centration except for tensile strength while for dolomite; all properties are appreciably maximized at 20% except for maximum strain.

© 2012 woaj Ltd. All rights reserved

Faith U. Babalola* and Paul O. Erhievuyere-Dominic Department of Chemical Engineering, University of Lagos, Lagos, Nigeria

Article history: Received: Revised: Accepted: Available online: 6 March 2012 Keywords: Calcium carbonate, Dolomite, Polyurethane, Foam, Fillers

A R T I C L E I N F O A B S T R A C T

Innovations in Science and Engineering 2 (2012) 34-40

1. INTRODUCTION The commercial products known as polyure-

thanes are chemically complex polymeric materials usu-

ally formed by the reactions of liquid diisocyanate com-ponents with liquid polyalcohol components. Rigorous research led to the first laboratory produced flexible foam in 1941 (Bayer; 1947).

Foam production technology was introduced to

Nigeria in 1964 (Makanjuola; 1998) and since then there has been tremendous improvement which has made polyurethane foam a versatile and high quality cushion-ing material suitable for several purposes.

Corresponding author. email address: [email protected] 2012 woaj Ltd. All rights reserved

Available at woaj

Innovations in Science and Engineering

Journal homepage: www.woaj.org/ISE

35


Polyurethane foams are made up of solid-gas composites in which the continuous solid phase provides structural and mechanical characteristics such as hard-ness, resilience, load bearing ability, compressibility and containment for the gas phase. The earliest foams which were made using polyester alcohols soon gave way to polyurethane foams which were made using simpler and cheaper production processes involving reactions at lower pressures and also possessed generally better foam qualities. Due to the versatility of polyurethane foams, a variety of foams with different densities and hardness can be produced for very wide applications. These applications include furnishings for homes, rec-reation and institutions, packaging, lagging, sound con-trol and vibration dampening installations (Klempner and Sendijaveric, 2004). This work investigates the ef-fects of calcium carbonate (calcite) on foam properties in contrast with that of dolomite as fillers. Since both compounds are readily available, cheap, suitable as fill-ers and involve almost exactly the same cost implica-tion, our analysis leans almost entirely on their effects on the structural and mechanical properties of foams produced.

2. LITERATURE REVIEW

The production of foam, which is a member of the family of polymeric compounds, began with latex as the major raw material in the early thirties (Bayer; 1947). The first foams were produced using polyester alcohols but were unable to withstand in-door tempera-ture and humidity conditions. They also often failed by crumbling away; as a result they were quickly replaced by polyurethane foams made from polyether polyols (Herington and Hock; 1997). These had better perform-ance since they were less affected by hydrolysis, were more durable and more comfortable. These two kinds of foams are contrasted in Table 1.

Raw Materials

The raw materials used in the production of flexible polyurethane foams can be grouped into four (Saunders and Frisch; 1994): Main materials- polyol and isocyanate - The polyol forms the backbone of the polymer chain since it serves as the source of the hydroxyl for the isocyanate which determines the hardness of the foam Catalysts and activators - stannous octoate, amine and silicone - Stannous octoate is an organic-metallic cata-lyst for the reaction between the polyol and the isocy-anate while the amine catalyzes the reaction between water and the isocyanate. Silicone however is a surfac-tant which lowers the bulk surface tension of the react-ing mixture and stabilizes the foam bubbles formed. Blowing agents - water and methylene chloride- These, being sources of active hydrogen, react with isocyanide to produce carbon dioxide which causes the foam cells to rise. Additives - Fillers, colours and flame retardants - Fillers increase density, colours give the desired colour and flame retardants inhibit ignition which is a serious haz-ard posed by the highly exothermic reaction between water and the isocyanate. The Effect Of Fillers

Fillers are finely divided inorganic compounds which are purposefully added to foam formulations in order to increase their density, load-bearing ability and sound attenuation capacity at the expense of some un-desired physical properties as well as some desired properties but to a safe degree. Also, depending on the

Table 1: Contrast Between Polyester and Polyether Foams

POLYESTER FOAMS POLYETHER FOAMS

Rigid foams which are easily crumbled Flexible foams with more workability

Production is carried out using a relatively compli-cated and expensive high-pressure machine

Production is carried out using a simple low-pressure machine

Pre-mixing of chemicals before production is required Chemicals are metered separately and mixed during production

Has higher tensile strength Has lower tensile strength

Higher cost of production Lower cost of production

Possesses poor elasticity Possesses better elastic quality

36


nature of the filler used, significant cost reduction can be achieved. These fillers sometimes perform compli-cated roles during the chemical reactions of the polyure-thane formation; this is because reactive filler groups on the surface can react with the diisocyanate and change the balance in the disocyanate–polyalcohol reaction. At higher concentrations, fillers have the tendency of in-creasing the viscosity of the reaction mixture which af-fects the cell growth process thus changing the cell ge-ometry and consequently some physical properties of the foam (Erhievuyere; 2008). Typical examples of these fillers include the many grades of barium sulphate and calcium carbonate whose average filler concentra-tion is between 20 and 150 parts per hundred (pph) but may vary with application and from one country to an-other. In Nigeria, the control is strong and the range is kept between 1 and 50 pph. (Makanjuoka; 1998). Basic Chemistry

The basic chemistry in the production of poly-urethane foam involves the reaction of isocyanates with active hydrogen-containing compounds (especially alco-hols). Isocyanates are compounds having one or more of the highly reactive isocyanate groups (-N=C=O). The polymerization reaction is the polyurethane polymer-forming reaction which occurs between the di-functional isocyanate and the polyol in stages to form the complex polymer structure.

The gas-producing (blowing) reaction intro-

duces bubble gas to expand the foam being formed (Burst et al., 1960). This gas is carbon dioxide obtained from the exothermic reaction of isocyanate with water thus

Foam production is carried out in two stages; box foaming is first carried out on a laboratory scale in order to test the suitability of raw materials, determine the level of catalysts, carry out modifications and de-velop appropriate formulations for the industrial (large) scale production. The laboratory box foaming is then scaled up in the industrial or commercial foaming ma-chine.

3. EXPERIMENTATION

In this work, laboratory scale box forming was employed to produce foams at various filler concentra-tions using calcium carbonate and dolomite while run-ning a reference box foaming with no fillers at all. The produced foams were allowed to cure for more than 24 hours. Density tests were carried out to ensure an aver-age density for all foam samples. Other tests namely compression coefficient test, support factor and tensile strength tests were also carried out.

Apparatus: Box foamer, mixer, stop watch, weighing balance, beakers, mixing plate and lining paper.

Procedure: The required quantities of chemi-cals for the foam formulation were calculated and weighed out into a mixing plate in the order- polyol, water silicone, surfactant, amine, catalyst and finally the tin catalyst (stannous octoate) while the isocyanate was weighed in a separate beaker. The order of mixing has an effect on the final texture of the formed foam. Rigorous mixing was done until a uniform whitish colouration was achieved. The isocyanate was then added and further mixing was done until the beginning of reaction was observed by the appearance of a unique white colouration and the mix was poured into the foam-ing box and reaction timing began. Rising progressed along with the reaction and stopped at the end of reac-tion when timing also stopped. Five minutes after the end of rising, the foam blocks were removed and the sample was left to fully cure for above 24 hours to en-sure complete curing. The cured foam blocks were cut into required sample sizes. This was repeated for all the filler compositions – 5,10,15,20,35 and 30%. The maxi-mum value of 30% was chosen in keeping with the Ni-gerian high standard upper limit of 33% The samples were subjected to compression and elongation tests us-ing the compression set and indentation force deflection test using the indentometer.

4. RESULTS AND INTERPRETATION

The results (readings) obtained from the meas-

urements and calculations were interpreted using well established standards to obtain the desired parameters needed for characterizing the foam samples(Graf and Schendlowski; 1992). These parameters are as discussed below.

Density Determination

This was calculated from the measurements of the mass and volume of each foam sample. Density of foam gives it the needed weight for load-bearing ability and sound attenuation. The formulations were such that

37


variations in densities were maintained at the barest minimum to satisfy commercial standards. Figure 1 shows the approximately constant density for all foam samples

Compression Coefficient Determination

This measure expresses the degree of firmness or softness of foam. The higher the compression coeffi-cient, the firmer the foam. This test also gives a measure of the recoverability and resilience of foam. Compres-sion coefficient was determined using the formula

Compression coefficient was plotted against filler con-centration as shown in Figure 2 Support Factor Determination

The support factor in a grade of foam is some-times the most important measure because this dictates how much weight or load factor the foam will support. The support factor is largely dependent on the foam compression and the foam density. Support factor, which is a measure of the cushioning ability of foam, was calculated for each sample using the standard for-mula

The result is plotted against filler concentration and is shown in Figure 3. Tensile Strength Determination

The strength of the foam samples under tension as well as their elasticity were determined from the elon-gation test results. The strain, stress and modulus of elasticity at breakpoint for each foam sample were cal-culated using standard formulae.

Maximum stress, which is the stress experi-

enced by the foam sample at breakpoint was calculated using the standard expression

Where K = 0.1414 Maximum stress is plotted against filler concentration in Figure 4

Maximum strain, a measure of the elasticity of the foam, was determined from the elongation test using the expression

The plots for maximum strain against filler concentra-tion are shown in Figure 5 The tensile strength or modulus at maximum stress is calculated thus

It is a measure of the strength of foam under tension as well as its elasticity. For tensile strength (or modulus at maximum stress) against filler concentration, the plots are shown in Figure 6.

5. DISCUSSION OF RESULTS

Density is a measurement of the mass per unit

volume in polyurethane foams. It is important to the type of usage the foam will receive. Simply put, the higher the density the longer the foam will last. It is clear from Figure 1 that the density of the foam samples which was controlled from the formulation of the mix-ture was fairly successfully kept constant. The minor variations may be attributed to imperfect mixing and slight measurement errors.

Figure 2 shows the compression coefficient

obtained from the indentation force deflection test. The maximum value for calcium carbonate-filled foam was 12% at 30% filler concentration while for dolomite-filled foam it was about 15% at 10% filler concentra-tion; also worthy of note is the irregularity in the varia-tion of the compression coefficient with filler concentra-tion for both fillers.

As shown in Figure 3, there was very little

variation in the support factor of foam samples with both fillers. Foams with high resilience also have high support factor. It is a strong measure of foam quality. It is evident however that dolomite had the highest value of about 2.8 at 25% concentration

Maximum stress is a measure of the ability of

the foam to withstand stress during elongation the higher the maximum stress, the more the foam can with-

38


stand tear when pulled. Figure 4 shows this plot for both fillers. For filler concentrations of less than 10%, the values were higher for calcium carbonate; but from 10% upwards, dolomite had much better performance than calcium carbonate.

From Figure 5, it can be seen that calcium car-

bonate –filled foam had its maximum strain of 400 at 10% concentration, dropped sharply to 150 at 15% and continued to drop gently with increase in filler concen-tration. For the dolomite-filled foam, its maximum strain rose to a maximum value of 250 at 5% and then dropped slowly and steadily with increase in filler concentration.

Figure 6 shows that the tensile strength for cal-

cium carbonate-filled foam rose very slightly at very low concentrations to 0.7N at 5%, dropped sharply to its lowest value of about 0.25N at 10% concentration and then rose again with increase in concentration to its maximum value of about 0.9N at 30% concentration. The trend is somewhat similar for the dolomite-filled foam. It dropped slightly at low concentrations, rose sharply at 15% concentration and then remained almost constant until 30% concentration was reached.

Figure 1: Density versus Filler Concentration

Figure 2: Compression Coefficient versus Filler Concentration

39


Figure 3: Support Factor versus Filler Concentration

Figure 4: Maximum Stress versus Filler Concentration

Figure5: Maximum Strain versus Filler Concentration

40


6. CONCLUSION For calcium carbonate as filler, all properties

here tested were approximately maximized at 10% con-centration except for tensile strength which was at its minimum; but was maximized at 30% concentration. For dolomite as filler, all properties were appreciably maximized at 20% except for maximum strain which was highest at a concentration of 5%. Since maximum strain as a property is incorporated and reflected in the tensile strength, it is a weak factor to consider in foam quality. Hence the optimum concentration for calcium carbonate as a filler is 10% while that of dolomite is 20% Since the prices and densities of both fillers com-pared in this work are approximately the same, we can conclude that dolomite at 20% concentration is preferred to calcium carbonate at 10% as this will translate to 100% more cost reduction and yet yield equally high quality foam. 7. REFERENCES 1. Bayer, O. (1947) Polyurethanes. Mod Plastics pp 24

-38.

2. Burst, J. M., Hurd, R. and Lowe, A. (1960) Poly-urethane Foams; Methods of Production, Properties and Applications. Chem. and Ind. pp 1544-1558.

3. Erhievuyere-Dominic, O. P. (2008) Comparative Study of the Effect of Calcium Carbonate and Dolo-mite as Fillers in the Manufacture of Polyether Polyurethane Foams. A BSc. Thesis, Department of Chemical Engineering, University of Lagos, Ni-geria.)

4. Graf, W. C. and Schendlowski, H. (1992) Automa-tion of Compression and Tensile Testing of Ure-thane Foams: Proceedings of the SPI-3rd Interna-

tional Cellular Plastic Conference. The Society of Plastic Ind. New York. pp 225-235.

5. Makanjuola, O. (1998) Handbook of Flexible Foam Manufacture. Vitafoam Nig. Plc. pp71-129.

6. Kklemper, D. and Sendijaveric, V. (2004) Hand-book of Polymeric Foams and Foam Technology. 2nd Ed. Hanser Publishers. Munich. pp 339-378.

7. Herington, R. and Hock, K. (1997) Flexible Poly-urethane Foams. 2nd Ed. Dow Chemical, Form No. 109-01061 7.2-7.3 A.13.

8. Saunders, J. H. and Frisch, K. C. (1994) Polyure-thanes: Chemistry and Technology Part II. Technol-ogy Interscience Publishers New York. Vol. 4, Is-sue 3. pp 193-200.

Acknowledgement The management and staff of VITAFOAM Nigeria, Plc, Lagos, Nigeria are gratefully acknowl-edged for their cooperation in allowing usage of their foam materials, foaming facilities and technical exper-tise for this work

Figure 6: Tensile Strength versus Filler Concentration

carbonato exp

Documents