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Bio-based Adhesives – Reclaiming Waste

Thorsten Leupold – Jul 13, 2018

TAGS:  Natural-based Adhesives      Bio-based Polymers    

Bio-based Adhesives – Reclaiming Waste Modern society consumes vast amounts of fossil resources for the production of everyday items, such as:

  • Cosmetics
  • Clothes
  • Chewing gums
  • Cars
  • Plastics, and
  • Comparably minor share, adhesives

Today, half of the adhesives used within the A&S industry already are water-based starch. However, conventional starch shows properties inferior to the practicability of more sophisticated, petrochemical-based adhesives like polyurethane.

Therefore, starch is mainly used in less demanding applications, not requiring resistance to water, high temperatures or shear stress. So, bonding corrugated board/carton and wall covering are typical areas of the application using starch as the base polymer.


Flexible packaging and other applications in the electronic or automotive industries, however, require robust, durable adhesives withstanding harsher conditions. Petrochemical-based adhesives meet these demanding requirements at low costs and hence are the method of choice in most cases.

Nowadays, petrochemical-based polymers dominate the adhesives market as they show feasible properties at much lower raw material prices compared to their bio-based counterparts. Polyurethane is created through a subsequent reaction of two components: isocyanates and polyols. Purity, molecular homogeneity and chemical constitution of both of the educts play a crucial role for the final adhesive’s properties. Well-defined chemical characteristics are usually associated with distinct, tunable properties to meet industrial expectations.

However, increasing petroleum prices in recent years along with ongoing restrictions on low-emission adhesives, responsible handling and smart utilization of industrial waste have enhanced general interest in bio-based polymers.

Let’s take a look at the sources of bio-based polymers and their future aspects for adhesive market...


Bio-based Polymers


In literature, the term bio-based is often confused with biodegradable. But the fact is that bio-based refers to materials obtained from renewable resources, such as:

Difference between Bio-based and Biodegradable
  • Corn
  • Potatoes
  • Starch
  • Rice, and
  • Other carbohydrates

Whereby, biodegradable describes physical and chemical changes of materials being metabolized by microorganisms. Moreover, biodegradable must clearly be distinguished from disintegration, meaning the respective material getting chopped up into smaller fragments without the production of CO2, CH4 or H2O.

However, in most cases, bio-based does also imply biodegradable as for instance in polylactic acid and starch. On the other hand, there are examples like polycaprolactone, synthesized with derivatives of hexanes making it non-bio-based but still biodegradable.

Generally, countries around the globe do have a similar perception of the term biodegradable, with minor differences. Example, the following listed regulations either contain testing methods for the ascertainment of biodegradability or setting standards for the declaration of biodegradability:

  • European Union’s EN 13432
  • United States’ ASTM D-6868 and ASTM D-6400
  • China’s GB/T 20197-2006
  • Japan’s JIS K 6953, as well as
  • Internationally recognized and widely accepted ISO 14855

These regulations claim decomposition rates of 60-90% to be achieved after a testing period of three to six months.


Manufacturing of Bio-based Polymers


In most cases, bio-based polymers’ production is conducted by fermentation, already having undergone historic changes. First generation bio-based polymers were produced directly from agricultural feedstock like corn or potatoes. This initiates an ethical debate about the utilization of food-related materials for non-food products.

This fuel versus food debate along with concurrent major breakthroughs in biorefineries and biotechnology induced a shift towards non-food materials. These are cellulose found in the waste of the wood and paper industry (second generation), or unused organic elements of spinach, coffee or cauliflower with bacteria, algae or yeast strains (third generation).

  • Currently, first generation bio-based materials are still the most common solution using corn or sugar cane as a hydrocarbon source. It is the cheapest and easiest process and thereby will most likely sustain for the upcoming years.
  • The second generation solution using the waste of agricultural products is currently in the rising phase. Especially, corn stover is used quite commonly as it is easily available.
  • The third generation is still in the development phase as the biotechnological processes are still very difficult to handle in downstream processing. Additionally, the usage of unused organic elements leads to extremely low yields and thereby very high production costs.

Succinic acid is frequently used for the production of polyester polyols which are important materials for the manufacturing of polyurethane. Metabolization of carbohydrates by bacteria or fungi leads to the desired succinic acid but also creates unwanted byproducts, such as other carbohydrates, proteins, amino acids as well as succinic acid salts. Resulting from that is a subsequent and necessary downstream processing characterized by the application of various purification techniques, e.g.:
Priority for Biopolymers
  • Electro-dialysis
  • Acidification
  • Extraction
  • Filtration
  • Vacuum distillation, and
  • Crystallization

Therefore, the total production costs for bio-based succinic acid are significantly increased by a series of comprehensive purification steps.

The top priority for bio-based polymers has to be productive at equal costs with purification degrees similar or superior to those of petrochemical-based molecules. In order to achieve this goal, production needs to become economically viable through further development and/or improvement of certain aspects. These would be logistics of biomass feedstock, new microbial strains and enzymes granting higher yields and less byproduct formation, more efficient downstream processing in order to obtain polymers with processable purity.

When price and quality of bio-based polymers reach that of petrochemical-based polymers; it is highly likely for companies to switch feedstock for greener image and sustainability aspects.

Characteristics 1st Generation 2nd Generation 3rd Generation
Feedstock source Sugar / starch source, sugar cane, corn, etc. Lignocellulose biomass, e.g. corn stover Biotechnological production, e.g. bacteria or algae
Advantages
  • Does not require petrochemicals
  • Does not require petrochemicals
  • Non-food feedstock
  • Does not require petrochemicals
  • Non-food feedstock
  • Flexibility target molecules
Challenges /
Disadvantages
  • Further scale up of production and reduction of feedstock costs
  • Mainly relies on food-feedstock and thus has rivalry with food production
  • Currently most efficient process
  • Process optimization to enhance conversion of feedstock material
  • High energy costs
  • High downstream processing costs
  • Still less efficient process
  • Large scale production and increased efficiency in extraction process
  • High downstream processing costs
  • Still less efficient process


Examples for Bio-based Adhesives and Raw Materials


Raw Materials for Bio-based Adhesives
Bio-based polyols used for the preparation of adhesives are available from:


In order to obtain polyurethane, the required isocyanate is purchasable from:


The Technical Research Centre of Finland, VTT, has developed novel starch-based adhesives used as hotmelt in applications requiring state-of-the-art processing methods. VTT claims that its technology fits applications such as packaging, paper, construction, and others.

In 2013, Henkel and DaniMer Scientific started a cooperation to develop bio-based hotmelt adhesives for consumer packaging, including end-of-line applications and labeling. Currently, Henkel offers acids and amine-based hotmelts under its Macromelt brand.


Bio-based Adhesives Market


The paper and packaging segment represents the largest share in the global bio-based adhesives market, followed by construction, wood, personal care and medical. Paper and packaging is the underlying market for starch-based adhesives and is expected to witness a healthy growth in the foreseeable future. Ever-increasing regulatory requirements towards low-emission adhesives are expected to fuel the demand for bio-based and biodegradable adhesives.

Major Application of Bio-based Adhesives


In addition, the crude oil price increased steadily in recent years causing for bio-based polymers to become competitive at a given break-even point. Further advantages of bio-based adhesives are easier recyclability, much less CO2-footprint than their fossil counterparts and thus a great marketing tool.

Apart from all positive aspects, the bio-based adhesives market suffers from various obstacles.

  • As mentioned above, the production of byproducts during fermentation demands comprehensive and cost-intensive downstream processing, subsequently increasing overall production costs and thus preventing price competitiveness with petrochemical-based adhesives.
  • Additionally, low shelf-life together with continuous usage of conventional adhesives further hinders the major breakthrough of this technology.
  • Finally yet importantly, limited performance capabilities compared to petrochemical-based adhesives, and regulatory measures for the medical sector form major obstacles to be mastered by bio-based adhesives producers.


Summary and Outlook


This article describes the perception of biodegradability around the globe, manufacturing processes of bio-based polymers, their utilization in the adhesives market as well as trends for the foreseeable future.

The key market for bio-based adhesives is the paper and packaging segment with healthy growth to be expected for the next years, therefore representing a solid market for bio-based adhesives.

The production process of bio-based polymers through fermentation of cellulose-based (second generation) and other (third generation) feedstock still calls for improvement of biotechnology to be able to obtain higher yields and fewer byproducts. Improved enzymes/strains would thus decrease downstream processing costs, leading to cost-competitiveness of bio-based polymers with their petrochemical counterparts.

Overall, bio-based polymers can have properties similar to their conventional equivalents and are proven to be more sustainable with a lower overall CO2-production throughout the complete manufacturing process. With further biotechnological breakthroughs and following lower production costs, ultimately, bio-based polymers are likely to dominate the adhesives industry at the expense of their petrochemical-based counterparts.

However, in the foreseeable future obstacles in production processes and price issues will make a fast adoption in the adhesives world very unlikely. Large applications with lower requirements like plastic packaging will be urged much more to use bio-based polymers as they have a significantly larger share of the overall polymer usage and are thereby much more in focus of regulations and the public. Therefore, a high penetration of bio-based adhesives will most likely be seen in a far more distant future.


Commercially Available Grades for Bio-based Adhesives





Source: https://www.schlegelundpartner.com/en/



1 Comments on "Bio-based Adhesives – Reclaiming Waste"
Marco-Aurelio De P Oct 10, 2018
Very well discussed subject.

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