TAGS: Natural-based Adhesives Bio-based Polymers
This article was first published on Jul 13, 2018 and is revised on Jun 15, 2020.
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:
- 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 CO
2, CH
4 or H
2O.
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.:
- 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
Bio-based polyols used for the preparation of adhesives are available from:
In order to obtain polyurethane, the required isocyanate is purchasable from:
Apart from bio-based polymer manufacturing, recently we have seen
advances in renewable raw materials as well as R&D, such as:
-
A new class of furalkamines is developed, which is a new form of Mannich base curing agents, derived from pentosane-rich biomass. They are suitable for use as curing agents or modifiers to formulate solvent-free or high solids, low VOC maintenance specialized marine coatings, flooring, and adhesives.
-
Cardolite has launched ‘Cardolite® NX-9014’ – a multi-functional, sustainable polyol suitable for formulating polyurethane-based structural adhesives and sealants. According to Cardolite, adhesives based on NX-9014 deliver high tensile strength and hardness while still maintaining good elongation, thus, offering excellent bond strength to metals including challenging substrates like aluminum.
» Also Read: Cashew Nutshell Liquid (CNSL) Diols Bring Sustainability in PU!
-
Castor oil and black pepper for bio-based tunable adhesives – A new type of self-stick or pressure-sensitive adhesives based on castor oil and black pepper offer both sustainability and tunable properties. These adhesives are found to have 71% of renewable biological products. Researchers from POLYMAT Institute at the University of the Basque Country used 2-octyl acrylate from castor oil, and piperonal, found in black pepper.
The researchers blended the two raw materials under the same conditions that would be used in emulsion polymerization. The researchers then performed standard adhesive tests on the resulting polymers to determine that the materials worked as well as commercially available PSAs. They also discovered that by exposing the material to UV light, they could tune the material’s strength, stickiness, and shear resistance, thus, opening new possibilities for dental adhesives and structural adhesives that rely on UV-light curing.
Castor Oil and Black Pepper
-
Better adhesive strength & sustainability with tannic acid – Purdue researchers have developed a tannic acid-based sustainable solution for use as a hardener to improve properties of epoxy adhesives. Tannic acid is a naturally occurring polyphenolic compound. Using a tannic acid-based solution as a hardener, researchers found that this sustainable option offers the same performance concerning durability, stability, and stiffness at high-temperature and less environmental impact. The team is now looking for additional partners and those interested in licensing the technology.
-
Alternative feedstock to produce bio-surfactants – An innovative project at the University of Portsmouth involves the use of bails of rice straw to create bio-surfactants as a potential alternative for the synthetic surfactant molecules. Rice straw is a natural by-product of the rice harvest, with millions of tons created worldwide every year.
According to the researchers, biosurfactants created from rice straw or other agricultural waste could have a positive ecological effect in a number of ways and offer tremendous potential for applications in a range of industries.
Alternative Feedstock to Produce Bio-surfactants
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.
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 CO
2-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 CO
2-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/