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CNSL PropertiesCashew Nut Shell Liquid (CNSL)

CNSL Viscosity Explained: How Thick is Cashew Nut Shell Liquid?

By 16 May 2024No Comments7 min read
Diagram of CNSL molecular structure highlighting its diverse chemical composition

Cashew Nut Shell Liquid (CNSL) is one of the lesser-known byproducts of the cashew industry, yet it holds a significant potential in a variety of industrial applications. This natural resin-like material is extracted from the soft honeycomb structure inside the hard shells of cashew nuts and is known for its unique chemical properties, including its viscosity. Understanding the viscosity of CNSL is crucial because it affects how the liquid can be processed, handled, and utilized across different industries. This blog post aims to explore the viscosity of CNSL, how it compares to other natural oils, and its relevance in commercial and industrial contexts.

1. Composition of CNSL

Cashew Nut Shell Liquid is a dark brown, viscous liquid obtained from the pericarp fluid of the cashew nut. The main constituents of CNSL are anacardic acid, cardol, and cardanol. These phenolic lipids make up about 70% of CNSL, with the remainder consisting of minor amounts of polymeric materials and other substances.

2. Extraction Methods

The extraction of CNSL is traditionally done through roasting, where the shells are heated to release the liquid. However, this method can affect the quality and properties of CNSL due to thermal decomposition. More modern methods include cold pressing and solvent extraction, which are better at preserving the integrity and purity of the liquid.

3. Main Components and Their Characteristics

  • Anacardic Acid: Primarily responsible for the antimicrobial and anti-inflammatory properties of CNSL.
  • Cardol: Similar to anacardic acid but less abundant.
  • Cardanol: Known for its thermal stability and flexibility; widely used in industrial applications like resins and coatings.

These components give CNSL its unique properties and make it a valuable resource for various industrial applications, especially in areas requiring natural, sustainable materials.

Cashew Nut Shell Liquid (CNSL)

Basics of Viscosity

1. Definition of Viscosity

Viscosity is a measure of a fluid’s resistance to gradual deformation by shear stress or tensile stress. For liquids, it corresponds to the informal concept of “thickness”. For instance, honey has a higher viscosity than water.

2. General Factors Affecting Viscosity

The viscosity of a fluid can be influenced by several factors, including temperature, pressure, and the molecular composition of the fluid. In natural oils like CNSL, the type of constituents and their concentrations play a critical role in determining viscosity.

3. Importance in Industrial Applications

Understanding viscosity is essential for industries as it affects the fluid’s pumping requirements, mixing capabilities, and stability in formulations. This is particularly important in the paint and coating industry, where precise viscosity measurements are crucial for the application and performance of the product.

Viscosity of CNSL

1. Specific Viscosity Characteristics of CNSL

Cashew Nut Shell Liquid (CNSL) exhibits a unique viscosity profile that distinguishes it from other natural oils. Its viscosity can vary significantly depending on the extraction method and the processing conditions. Typically, CNSL has a higher viscosity than more commonly used natural oils like coconut or palm oils. This higher viscosity can be attributed to the larger molecular size of its phenolic constituents and the presence of natural polymers.

2. Comparison with Other Natural Oils

When compared to lighter oils, CNSL’s higher viscosity makes it more suitable for applications requiring a robust, durable material. Its viscous nature also contributes to its efficacy as a binding agent in resin and coating applications, where it imparts superior water resistance and mechanical strength.

3. Factors Affecting CNSL’s Viscosity

The main factors affecting the viscosity of CNSL include:

  • Temperature: Like most liquids, CNSL becomes less viscous as temperature increases. This characteristic is crucial for processing CNSL in industrial settings.
  • Purity and Composition: The proportions of anacardic acid, cardol, and cardanol can influence the overall viscosity. More homogeneous mixtures tend to have a more consistent viscosity profile.
  • Age and Storage Conditions: Over time and under exposure to air, CNSL can undergo polymerization or oxidation, which can increase its viscosity.

Understanding these factors is essential for optimizing the use of CNSL in industrial applications, particularly in formulations where viscosity is a critical parameter.

Measurement Techniques

1. How Viscosity is Measured

Viscosity measurement can be performed using several types of viscometers, with the choice depending on the precision required and the nature of the liquid. Common instruments used include:

  • Rotational Viscometers: These are most commonly used for CNSL due to their ability to measure a wide range of viscosities.
  • Capillary Viscometers: Although less common for viscous fluids like CNSL, they are used for precise measurements under controlled temperature conditions.
In the Polymer and Resin Industry

2. Instruments Used for Measuring CNSL Viscosity

For industrial applications, the Brookfield Viscometer is often used due to its robustness and accuracy for viscous liquids like CNSL. This type of viscometer can provide reliable data that helps in formulating products and in quality control processes.

3. Challenges in Measurement

Measuring the viscosity of CNSL poses specific challenges:

  • Temperature Control: Since CNSL’s viscosity changes significantly with temperature, maintaining a constant temperature during measurements is critical.
  • Sample Preparation: Ensuring the CNSL is free from particulates and has not significantly oxidized before measurement is crucial for obtaining accurate readings.

Applications of CNSL Based on Viscosity

CNSL’s unique properties make it highly valued in several industrial applications:

  • Resins and Coatings: Used in the production of friction linings, varnishes, and paints due to its high thermal stability and chemical resistance.
  • Rubber and Plastics: Acts as a plasticizer and as a component in the production of specialty rubbers and composites.

The viscosity of CNSL influences its handling and processing in industrial applications. For example, in the coatings industry, the viscosity of CNSL affects the ease of application and the quality of the finish. High viscosity might require adjustments in the formulation or the processing temperature to achieve the desired flow properties.

CNSL offers eco-friendly benefits due to its renewable nature and the fact that it is a byproduct of cashew processing. Its use helps reduce environmental impact while providing functional advantages in products due to its durability and resistance properties.

Improving and Modifying CNSL Viscosity

The viscosity of Cashew Nut Shell Liquid (CNSL) can be manipulated to meet specific industrial needs through various techniques:

  • Temperature Control: Adjusting the processing temperature is a straightforward method to manage viscosity temporarily during the application or processing phase.
  • Chemical Modification: Addition of viscosity modifiers or reactants can chemically alter the molecular structure of CNSL components, thereby changing its viscosity. For instance, phenol-formaldehyde can be used to react with CNSL to form novolac resins, which are less viscous.
  • Blending: Mixing CNSL with other oils or solvents can adjust its viscosity to suitable levels for particular applications, such as in paint formulations or adhesives.

Common chemical modifiers used in CNSL include:

  • Aldehydes: These are used to cross-link phenolic components, decreasing viscosity for easier application in coatings and adhesives.
  • Epoxy Resins: When mixed with CNSL, they enhance the mechanical properties of the final product while adjusting the viscosity for easier processing.

These modifications not only help in tailoring the physical properties of CNSL but also enhance its functionality in diverse applications.

Further research is needed to explore more eco-friendly and cost-effective methods to modify CNSL viscosity. Innovations in enzyme technology and green chemistry could lead to more sustainable processes that maintain or enhance the functional properties of CNSL while making it easier to handle and apply in various industrial contexts.


Cashew Nut Shell Liquid (CNSL) is a remarkable natural material characterized by its unique viscosity and rich chemical composition. The intrinsic properties of CNSL make it a valuable resource in the production of industrial resins, coatings, and composites. Its viscosity plays a crucial role in its application and effectiveness in these areas, influencing everything from processing methods to the performance of the final products.

The future of CNSL looks promising, driven by a growing interest in sustainable and bio-based materials. As industries continue to seek environmentally friendly alternatives to synthetic chemicals, CNSL stands out as an effective solution that not only provides exceptional performance but also contributes to waste reduction and environmental sustainability.

Understanding the viscosity of CNSL and how to manipulate it is key to unlocking its potential in a broader range of applications. Continued research and development in this area are crucial for maximizing the use of CNSL, promoting its integration into new markets, and supporting the global shift towards sustainable industrial practices. The versatility and eco-friendliness of CNSL make it an invaluable material for the future, poised to make significant contributions to various sectors of the economy.

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