Phenolic Resins based on Card Phenol (Cardanol) (Technical Note: C - 16A)

General Typical Formulations Technical service

1.0 General

Cardanol represents the active constituent of CNSL where it is present as anacardic acid. It is mono hydroxyl phenol with C15H27 hydrocarbon side chain substituted in the meta position.

The side chain is known to have an average of two unsaturated bonds, some of the superior properties which the Cardanol based resins have compared to resins based on conventional synthetic phenols have been attributed to the nature of its bulky hydro carbon side chain.

The trifunctionality of the phenol is retained while the reactivity at one or the two positions in the benzene ring is reduced due to the long side chain. This is favourable to the formation of oil soluble resins similar in properties to those derived from substituted phenols with the added advantage of internal plasticisation, higher solubility in aromatic and aliphatic solvents as well as better resistance of water, acids, alkalies and solvents such as ethanol etc. The long side chain also confers flexibility to the films even after baking and the unsaturation helps fast polymerisation and uniform drying of the film. The higher solubility of its resins in oils is explained by the Meta substitution of the hydrocarbon chain.

The films of Cardanol based resins are also known for their superior electrical properties.

For improving their colour and hardness other phenols like carbolic acid, cresol, para tertiary butyl phenol etc., can be added to Cardanol in various proportions.

1.1 Novolac and Resol Resins: Cardanol is very suitable for manufacturing both Novolac and Resol resins.

When used with acid catalyst and less then one mole of formaldehyde is reacted with one mole of Cardanol, Novolac resins are yielded. These resins are flexible and are not hardened by heat, which is their typical characteristic. Resol Resins can be manufactured by reacting more than one mole of formaldehyde per mole of Cardanol in the presence of an alkaline catalyst. These resins are hardened by heating and ultimately changing to insoluble gel.

1.2 Oil and Alcohol soluble resins: Normally the resins based on Cardanol are oil soluble. It is however, possible to manufacture alcohol soluble resins also if the reaction is arrested at the proper stage. Resins based on Cardanol and phenol in the ratios of 1:3 are also alcohol soluble.

2.0 Typical Formulations

Some typical formulations using Cardanol or its admixtures with other phenols and the properties of the resins so obtained are given in the following. These should be regarded only as indications of the possibilities.

2.1 Resols based on pure cardanol: When Cardanol is reacted formaldehyde in the presence of ammonia catalyst, resins in soft form are obtained. But when sodium hydroxide is used as catalyst the products are generally viscous or almost semi-solid products.

It occurs because ammonia not only acts as a catalyst but also enters into condensation reaction to give amino methylene linkages, generally resulting in products of high melting points.

2.11 Method of Preparation with Alkali Catalyst: Cardanol readily reacts with compounds having an aldehyde and reactive methylene groups such as formaldehyde, acetaldehyde, furfuraldehyde, aerolein and hexamine etc.

In a typical formulation, one mole of Cardanol and 1.3 mole of formaldehyde are reacted together under reflux in the presence of either ammonia (28% W/W) or sodium hydroxide (10% aqueous solution). The proportion of formaldehyde can be adjusted to obtain resins with desired properties.

When sodium hydroxide is employed as catalyst some ethyl alcohol may be used to keep the reaction mixture homogenous. During the reaction Ph is maintained at 8 to 9. After the reflux is over, water should be distilled off at a vaccum of around 24.

If a kettle with refluxing arrangement is not available, hexamine can be used in place of formaldehyde. Cardanol is heated with stirring to 130°C and hexamine is added slowly during 20 minutes. The temperature is then raised to 148°C to 150°C and kept at that level till the smell of ammonia almost ceases.

2.2 Novolacs with Acidic Catalyst: The usual acidic catalysts are used either as oxalic, hydrochloric or sulphuric acids.

The procedure used is the same as above with the only difference that care should be taken to see that acid is washed out thoroughly before dehydration of the resin.

The properties of the above resins are given in the enclosed table.

2.3 Resins based on Mixtures of Cardanol and Phenols

2.31 When Cardanol and phenol are used in 1:1 molar ratio and reacted with formaldehyde resol or novolac resins are obtained depending upon the catalyst.

These are oil soluble and those manufactured with ammonia as a catalyst have fairly high melting points. They have light colour and can be used with advantage as a base for high quality varnishes.

2.32 Alcohol soluble resins based on Cardanol and Phenols: These resins have special applications in paper lamination industry. The presence of Cardanol upto 25% of phenol does not affect the solubility in alcohol but improves considerably by the properties of the resin. The machinability and punchability of laminates is improved along with their gloss and resistance to moisture and other diluted chemicals. Their electrical properties are also known to improve considerably.

Since Cardanol is comparatively less reactive then phenol, it is preferable to start reaction with Cardanol and formaldehyde first and then add phenol and further formaldehyde.

A) Alcohol soluble resins using ammonia as catalyst:

A typical formulation can be described as follows:

 

Cardanol 40 kg. Formalin 14 ltrs. (1.3 mole of Cardanol) Liquor ammonia 4 ltrs. (about 28% W/W Ammonia) Formaline 85 ltrs. (1.3 Mole of Phenol) Phenol 160 kg. Liquor Ammonia 16 ltrs. to keep PH at 8-9

Cardanol 40 kg is taken and (14 ltrs) of formalin (4 ltrs) of Liquor Ammonia are added and stirred at 140°C for about half an hour. Then (160 kg) of Phenol is added and stirred for some time till the mixture is homogeneous. Then formalin (85 ltrs) and liquor ammonia (16 ltrs) are added in small lots alternatively during half an hour keeping the PH at 8-9.

High molar ratio of Formaldehyde with Cardanol will give resins having lower curing time.

B) Alcohol soluble resins using caustic soda as catalyst: Cardanol (40 kg) is taken, to this 1.5 mole of formaldehyde is added in presence of ION solution of caustic soda in water, keeping Ph between 8 to 9. Some alcohol may be added to keep the solution homogeneous. The temperature is maintained at about 60°C and refluxed, the phenol 160 kg and 1.5 mole of formaldehyde as formalin are added along with caustic soda solution to keep Ph between 8 to 9. Alcohol can be added to keep solution homogeneous. Stirring and refluxing is done for about one hour.

The above resin is comparatively cheaper and is very suitable for decorative laminates.

2.3 Improvement of phenol formaldehyde moulding powders with cardanol: Application of 10% or more of Cardanol on the weight of phenol while preparing phenol formaldehyde moulding powders improves their gloss, toughness and their flow properties. For the purpose of calculating the quantity of formaldehyde, the molecular weight of Cardanol can be taken as 300.

2.4 Resins based on Cardanol and Alkyl phenols: Mixtures of Cardanol along with phenols such as tertiary butyl phenol and tertiary amylphenol in the ratio of 1:1, this mole can be used for the manufacture of high quality light coloured resins. The proportions can be changed to suit special requirements. Combination of Cardanol with para-tertiary butyl phenol gives hard solid resins with ammonia as catalyst. With caustic soda as catalyst the resins are viscous semi-solid products.

The properties have been given in the enclosed table:

2.5 Cardanol Resin modified alkyds: Cardanol resin modification of alkyds not only reduces the cost of the alkyd considerably but also improves remarkably its properties. The varnishes based on such modified alkyds have better gloss and satisfactory flexibility in addition to their remarkably superior resistance against water, dilute chemicals and solvents.

The modified alkyd can be prepared according to the following procedure.

Cardanol 100 kgs. Hexamine 8 kgs. Long Oil linseed alkyd (66%) 100 kgs.

Cardanol is heated with stirring to 130°C and hexamine is added in small lots during 15 minutes. Temperature is then raised to 145°C and heated at that level till the smell of ammonia ceases. Then 100 kgs.of alkyd is added and temperature is raised to 250°C to 260°C and heated in an atmosphere of nitrogen or carbon-di-oxide till the string of about 18’’ is obtained.

2.6 Rosin modified Cardanol resins: To Cardanol (300 kg.) rosin ‘WG’ or ‘N’ Grade (130 kgs.) is mixed and formalin (90 kgs.) is added and refluxed for about 3 hrs. Water is removed under low pressure and material heated to 110°C – 120°C till reduced to absolutely dehydrated resin.

2.7 Styrenated Cardanol Resins: Styrenated Cardanol resin is excellently suitable for high quality paints and varnishes. The films of its varnishes are very hard and maintain their gloss over a long period. In fact, they have comparable properties to ployster films. Their drying time is also very much lower than that of the varnishes based on pure Cardanol.

A typical formulation can be described as follows:

Cardanol 300 parts Hexamine 24 parts Styrene 150 parts

Cardanol and hexamine are treated as above. Styrene is added and heated till reflux ceases and a string of 16 to 18’’ is obtained. The temperature during this process is raised slowly to 200°C to 260°C.

3.0 Technical service

Cardanol and its derivatives are manufactured by us in close technical collaboration with the Indian Institute of Chemical Technology,Hyderabad under the license from the NRDC. We also have our own well-equipped research and development laboratories and are, therefore in a position to provide detailed technical advice and suggestions for the application of this material.

3.1 Caution

Properties of Cardanol based resins