Development and Characterization of Phenol - Formaldehyde Molding Powder

 

M .O. Edoga and A.S. Kovo

 

Department of Chemical Engineering, Federal University of Technology, Minna, Nigeria

kovoabdulsalami@yahoo.com

 

 

Abstract

The synthesis of phenol-formaldehyde resin was carried out at pH 4.0-4.3, formaldehyde to phenol (F/P) of 0.881 in the presence of acid catalyst (hydrochloric acid and oxalic acid), at operating temperature and pressure of 115°C and 1 atmospheric pressure respectively. Forty-six grams of the resin produced was formulated into molding powder by incorporating the following: 44.6 grams of water-free- wood-floor, 6.7 g of hexamethylene-tetramine, 2.0 g of magnesium oxide and 1.0 g of magnesium stearate. The determination of pH, viscosity, specific gravity, refractive index, molecular weight and total solid content were carried out at 25°C for both the neat/ conventional P-F resin and the molding powder, while infrared spectrum was performed only on the neat P-F resin. The result obtained showed the sample with water-free-floor (sample y) has better mechanochemical properties than the neat sample (simple x). The results for both sample X and Y are: pH valve of 4.11 and 4.5, viscosity of 173.72 and 243.12 poise, refractive index for sample X was 1.67, molecular weight 16967.63 and 25234.54 respectively. The analysis of infrared spectroscopy of sample X showed that at region 3650-3590 cm-1, ­­­there was an absorption whose peak was between sharp and weak and is also O-H stretch-free indicating presence of phenol. The intensity of absorption at region 2800-2700cm-1 is medium indicating C-H stretching vibration of -CHO presence confirming aldelydes. Hence the physiochemical properties and the intra-red spectrum compared well with literature values.

Keywords

Phenol-formaldehyde, pH, Molding powder, Novolac, Infrared spectroscopy

 

 

Introduction

 

Phenol-Formaldehyde resin is a highly crosslinked thermosetting material that is produced by the poly-condensation of phenol and formaldehyde in the presence of either acidic or basic catalyst. An acid catalyst is usually used in preparing novolac type of resin. A novolac resin is produced if the mole ratio of formaldehyde to phenol (F/P) is greater than one [1]. The two processes in general use are the one-step process producing resole resins (which is the formation of a phenol resin) that are either liquid or brittle, soluble, fusible solids, and the two – step process, using an excess of phenol to produce novolac, resin that have no reactive methylol groups and must be mixed with an aldehyde to undergo further reaction.

Resole resin thermoset on heating, are used for adhesives [2]. Novolac require a further source of formaldehyde in the form of hexamethylene tetramine to produce molding powders [3]. Both resins are run out from the vessel after removal of water by distillation, and ground up, then compounded on heated rolls with filter that vary from wood flour to mica, for strength and heat resistance, fibrous asbestos is used as a filter (hexamethylene tetramine is also added at this stage in the case of the two-step resin). Final grounding produces the molding powder, which on further heat treatment will yield the typical thermoset resin.

The P-F resin has various applications. It can be used in resin form as a bonding agent. Subsequently, the liquid resin can be dried and ground into molding powder, which is usually used in molding electrical fittings. Buttons, television and computer housing and the other household articles for the purpose of the paper, emphasis will be on the preparation, processing and characterization of P-F resin and molding powder.

 

 


Experimental

 

Table 1. Material Used for the Experiment

Materials

Formula

Res.Code

Source

Comment

Phenol

C6H5OH

P10429

Nice Lab India

Solid

Formaldehyde

CH2O

40%w/v

May and Baker Ltd Eng

Liquid

Magnesium Oxide

MgO

UN1145

Avondale Lab Eng

Solid

Magnesium Stearate

Mg(C17H35COO)2

UN1147

,,

Solid

Sodium hydroxide

NaOH

00263G

Chemproha Chemicals Ned

Alkaline Pellet

Hydrochloride

HCl

UN1162

Avondale Lab. Eng

Acidic liquid

Oxalic acid

C2O4H2

UN1170

,,

Acidic

HexamethyleneTetramine

(CH2)6(NH3)4

UN1176

,,

Acidic Solid

Distilled water

H2O

NA

Chem. Lab FUT Nig

Liquid

 

Table 2. Equipment used in the Experiment

Equipment

Source

Research Code

Comment

Waterbath Regulator

Cliffon Eng

CE94

At 90-150°C

Oven

Gallenkamp Eng

N/A

At 160 °C

Double-jacketed Reactor

Quick fit Eng

N/A

Glass apparatus

Pump

Charles Pumps Ltd Eng

N/A

Glass apparatus

Stop Watch

Armfield Eng

N/A

Timer

pH meter

Kent In Ltd Eng

N/A

Digital display

 

 

Preparation of a phenolic Novolac

Thirteen hundred grams of phenol (13.8 moles) 130g of water, 145 parts of 30% aqueous formaldehyde (11.45 moles) and 6.5 parts of oxalic acid crystals were charged into a glass double jacketed reaction. The mixture is properly mixed using a mechanical stirrer while heating a mixture to boiling point and refluxed for 60 minutes (first condensation). Thirty-four and seventy-tenth parts of 15% hydrochloric acid, corresponding to 0.4% of 100% HCl on the weight of phenol were slowly added. The reaction mixture was refluxed for another 35 minutes (second condensation). The reason for the use of both oxalic acid and hydrochloric acid is that the reaction was more easily controlled at the beginning and the conversion was more completed at the end. When the second condensation was completed, 400parts of cold water was introduced and the reaction mixture was cooled to about 75°C. The crude resin was allowed to settle for 30 minutes. After removal of the supernatant layer of water, the resin was dehydrated without vacuum. As soon as the resin was cleared at 100°C, sodium hydroxide solution of 36% concentration was added to neutralize the resin; about 30-40% of the quantity equivalent to the acid used was required. The concentration was continued until the resin temperature reaches 115°C. The resin may be further heated for 5-10°C minutes under vacuum to degas it. The yield of the resin is about 110% of the weight of the phenol. The viscosity of the 80% resin solution in alcohol is 80-90cp. The properties of the product vary according to the formulation. This phenol resin is called novolac resin.

 

Preparation of phenolic moulding powder

The product obtained from the resin produced above (novolac) was divided and 46 parts of the resin was charged with 44.6 parts of water-free-wood-floor, 6.7 parts of hexamethylenetetramine, 2.0 part of magnesium stearate were charged at a jacketed mixer which was heated at 100-110°C, the charge attains a temperature of 60-65°C and mixed for 1.5-5 minute. The mixed material was than transferred to a roll mill with the front roll heated at about 95°C and revolving at 15rpm, and the rear roll at 65°C and 20 rpm. It was rolled for 2-25 minutes. Finally, the rolled material was crushed and granulated as moulding powder.

 

Characterization of the Resin

pH Measurement

The pH of the material (resins) produced was measured using pH meter electrode. 50 cm3 of the P-F resin was collected into a beaker and the pH value was determined by inserting the pH meter electrode into it. The pH value from the instrument was recorded.

Specific Gravity Measurement

The empty specific gravity bottle was weighed and its weight was recorded. The same specific gravity bottle was fitted with phenol- formaldehyde (RF) sample and weighed.

The difference in weight between the specific gravity bottle filled with the resin and empty specific gravity bottle gives the density.

Viscosity Measurement

The standard method of determining viscosity was employed using the viscometer bath and U-tube viscometer with capillary inserted into the viscometer bath. A quantity of the sample of P-F resins was poured into the U-tube viscometer with capillary and then corked.

The U-tube was suspended into the temperature of the viscometer bath containing water and the temperature of the bath was maintained constant. The cork was removed and the time taken for the content to run-up starting from the top mark to the middle mark was noted using a stopwatch.

This result was used in the calculation of the viscosity of kinematics, specific gravity, reduced viscosity and fluidity of the sample.

Refractive Index Measurement

A pint of the prepared resin was introduced into the prism chamber of the refract meter through the appropriate provision mad and allowed to stabilize for some time. The refractometer reading was taken by placing the refractometer under the sunlight, and the compensation ring of the refractometer was turned, until there was a sharp division (‘X’ sign) between the dark portions of the sample.

The accurate refractometer reading was taken bas the whole number and the decimal unit shown on the micrometer screw gauge.

Total solid content (TSD) Measurement

The total solid contents of the resins were determined by weighing 2g of the resin into a small aluminium dish. The dish was placed in an oven at 100°C for 2 hours and allowed to cool in desiccators. The dish was then weighed to find the weight of dry resin remaining. The result obtained was used to calculate the total solids content of the resin.

Infrared Measurement

Infra-red analysis was carried on the phenol-formaldehyde resin (novolae) using Perkin-Elmer 1310 and nunjol as solvent.

 

 

Results and Discussion

 

Table 3 gives the result of the physiochemical properties of the neat (novolac) and the modified P-F resin (moulding powder).

Table 3. Properties of the various samples of Phenol-Formaldehyde Resin

Property

Sample X

Sample Y

Iterative value

pH (at 25°C)

4.11

4.5

4-5

Viscosity (poise at 21°C)

173.72

248.12

-

Specific gravity (g/cm3 at 25°C)

1.13

1.41

1.47-1.52

Kinetic viscosity (stoke at 25°C)

153.73

176.22

-

Fluidity (poise-1 at 25°C)

5.76

-

-

Relative viscosity (at 25°C)

413.61

-

-

Specific viscosity (at 25°C)

412.61

-

-

Reduced viscosity (at 25°C)

385.98

-

-

Inherent viscosity (at 25°C)

5.64

-

-

Refractive index (at 25°C)

1.67

-

1.57-1.59

Molecular weight (g)

16967.63

25234.54

-

Operating temperature (°C)

115

115

115

Operating pressure (atm)

1

1

1

Total solids content (TDS) at 100°C (%)

63

71

640

The pH values of the sample X and Y at 25°C are 4.11 and 4.50 respectively; these values are considered reasonable as compared to the value obtained from the literature (4 - 5) for the standard P-F resin.

The specific gravity of sample X and Y are 1.13 and 1.41 glcm3 respectively; these are also within range in the literature which is 1.42-1.52 g/cm3.

The absolute viscosity (μ) of sample X and Y are 173.72 and 248.12 poise respectively at 25°C. This result shows that the modified P-H resin has a higher viscosity than the novolac resin. This is because of the addition of hexamethylene tetramine which increase the cross linking of the polymer and as a result of the addition of filter to modify the resin. Further more, the variation in the values can also be attributed to the fact that their values were not determined at the same time. The reaction often continues at room temperature and this lead to increase in molecular mass, which in turn has direct effect on viscosity.

Kinematics viscosity was also determined for both sample X and Y as 153-73 and 176.22 g/cm3 respectively. The result shows that the two samples are close when compared to each other. Fluidity was determined for sample X and is known as the reciprocal of viscosity.

Relative viscosity, specific viscosity, reduces viscosity and inherent viscosity at 25°C was also determined for sample X as shown in Table 3.

The refractive index at 25°C for sample X was determined to be 1-67. This value does not correspond to the literature value of 1-57-1.59. The discrepancy is as a result of not determining the refractive index of sample immediately it was prepared. This is because polymerization, continue even after preparation and therefore increases the molecular weight which leads to increase in the refractive index.

The molecular weight of the two samples X and Y shows that Y has the highest value of 25, 234.54 while that of X is 16, 967-63. The difference in the molecular weight of sample X and Y is due to the fact that filler-wood floor with magnesium oxide and magnesium stearate was added to sample Y which increases its molecular weight compared to sample X, it can therefore be deduced that sample Y will have a better mechanical properties compared to sample X.

Total solid content (TDS) at 100°C for both sample X and Y are 63% and 71% respectively. Although sample X correspond to the literature value of 64%, sample Y does not. The reason for the high value of sample Y is because the additions of wood floor which in turn increase the solid content and decrease the liquid content of the P-F resin.

Figure 1 gives the infrared spectrum of sample X at region 3650-3590 cm-1, there is an absorption whose peak is sharp and weak and is also 0-H stretch–free indicating the presence of phenols. At region 3025.28 cm-1 the intensity of the absorption is medium which an indication of N-H stretching vibration is, hence, primary amine group is confirmed present. The intensity of the absorption at region 2800-2700cm-1 is medium and indicate C-H stretching vibration of -CHO (2 bands) confirming the presence of aldelydes.

 

Figure 1. Infrared Spectra of Phenol-Formaldehyde Resin

 

At 1378-83cm-1 there is an absorption whose intensity is medium and indicate C-H band which confirm the presence of methyl, CH3 group. Furthermore, at region 1300-1150 cm-1, there is strong intensity of absorption with C-O stretch indicating the presence of acid.

 

 

Conclusion

 

Development and characterization of phenol – formaldehyde molding powder have been developed using phenol and formaldehyde as monomers to produce novolac resin which was fortified using wood floor to cure it to phenol-formaldehyde moulding powder. The analysis of infrared spectroscopy shows that the P-F resin produced has other unknown functional groups present (such as -CH3) from other chemical compound which were used as reagent in its preparation. This is because each chemical compound has a unique IR spectrum.

 

 

References

 

[1] Wei W., Hu H., You L., Chen G., Preparation of carbon molecular sieve membrane from phenol-formaldehyde Novolac resin [9], Carbon, 40(3), p. 465-467, 2002.

[2] Bousoulas J., Tarantili P. A., Andreopoulos A. G., Resole resin as sizing agent for aramid fibres, Advanced Composites Letters, 10(5), p. 249-255, 2001.

[3] Bauer R. S., Applications of epoxy resins in high density packaging, Polymeric Materials Science and Engineering, Proceedings of the ACS Division of Polymeric Materials Science and Engineering, 59, p. 626-628, 1988.