By Dr. Parul Thapar*1, Riya2
Introduction
Adhesives are non-metallic substances that are capable of joining materials by surface bonding (adhesion), with a bond possessing adequate internal strength (cohesion). Adhesion is the force of attraction between molecules in different layers.1 There are different types of adhesive materials depending on their characteristics and functions which are shown in Table 11-10:
Table 1: Types of Adhesives
|
S.No. |
Types of adhesives |
Characteristics |
Applications |
|
1. |
Bio-based adhesives |
Derived from renewable resources like lignin, starch and plant protein. They have high mechanical strength, excellent thermal stability and low initial viscocity. |
Used for wood composites, for manufacture of products like plywood and softwood. |
|
2. |
Ocular adhesives |
These are easy to use. They can potentially minimize post-operative complications. |
Substitutes for sutures in operational surgery. |
|
3. |
Cyanoacrylate adhesives |
Efficient with ease of application; feasible; adhesive strength; biocompatibility; polymerization in moist environment. |
Used in medicine and dentistry for oral wounds and surgical procedures. |
|
4. |
Epoxy adhesives |
Resistant to high heat and chemicals; high cohesion; elasticity and minimal shrinkage |
Automobile industries |
|
5. |
Emulsion/ Dispersion based adhesives |
High molecular weight, low viscous and good workability |
Used in paper packaging and food packaging |
|
6. |
Polyurethane adhesives |
High flexible and bonding strength |
Food packaging |
|
7. |
Water based adhesives |
Contain starch- dextrin or casein |
Food packaging |
Adhesives for Food Packaging
Based on the above mentioned characteristics, the adhesives used in food packaging are mentioned as following1:
- Emulsion/ Dispersion based adhesives: These are further of following types:
- Vinylacetate based homo and copolymer dispersions- These are used for production and processing of packaging made of paper. These can be utilized in different forms:
- Bags- Sugar bags, bread
- Cardboard and corrugated boards- Fruits/ vegatables
- Folding box- Side beam
- Pouches and snacks- Milk powder, flour
- Core and tube winding- Aluminium foil
- Pressure sensitive adhesives– These can adhere to the surface when gentle pressure is applied. These have permanent adequate cohesion. Application: Self-adhesive paper and film labels or tapes. Labels can be applied on food, such as, fruits and vegetables as well as sausages.
- Laminating adhesives- These include acrylic dispersions to produce multi-layer lamination of various films. These can be applied for retorts, acrylic dispersions are cross-linked with water-dispersible aliphatic polyisocyanates.
- Hot melt adhesives- These can be applied for carton and case closing. They can be applied for:
- Tray erection- fruits, vegetables
- Case and carton sealing- cereals
- Folding boxes- confectionary, biscuits and frozen meals
- Wrap around- chocolate
- Bag-in-box- Juice, wine
- Cold seals- These can be used in the temperature range of 15- 25°C. Applications- Ice-creams, chocolates and biscuits. Reclosable food packaging- chocolate bars
- Heat seals- These are used for lidding applications, where aluminium or plastic lids are bound to food containers. Application- Packaging of dairy products such as yogurts, plastic trays and instant noodle cups.
- Polyurethane adhesives: These have high flexibility and bonding strength.
Application- a) Bags for coffee powder and chips at room temperature (31°C) or low temperature (0-4°C).
- b) Flexible packaging of aggressive food stuffs such as fruit juices or liquid pet food- used for elevated temperature, which is found in pasteurization or retort applications.
- Water- based adhesives: These are the natural polymers, which are of different types:
Application: a) Adhesives containing starch (dextrin or casein)- used in labelling applications. Starch glues are widely used for production of corrugated boards.
- b) Casein adhesives- These are used for labels of cold and wet bottles.
- c) Colloidal adhesives- These adhesives contain tackifier resins, eg. Plastic bottles
Conclusion: Adhesive packaging for foods are durable and can preserve food for a long period of time than any other packaging materials. The adhesives can effectively resist water vapour with good transparency. Due to their high tensile strength, low packaging cost and multiple applications, adhesive packaging can be a boon for the food industry.
References
- Toenniessen, M. (2018). Packaging materials- adhesives for food packaging applications. A report by International Life Science Institute, pp. 4-32.
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6213312/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7037176/
- https://onlinelibrary.wiley.com/doi/full/10.1002/pts.2367
- https://www.nature.com/articles/s41467-019-13449-y
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5666723/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6889139/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6571881/
- https://www.researchgate.net/publication/230582585_Comparison_of_the_adhesives_used_in_food_packaging_multilayer_materials_and_migration_studies_from_packaging_to_food
- https://www.researchgate.net/publication/328573412_Effect_of_high-pressure_processing_on_characteristics_of_flexible_packaging_for_foods_and_beverages
Authors are 1*Assistant Professor, CT University, Ludhiana-142024, 2Student, CT University, Ludhiana-142024
