Real Bio-based Ingredients for Formulator's Toolbox

There are also many challenges to the full-scale commercialization of bio-polymers. The most severe market barriers include the following:
 

• Competition with inexpensive commodity materials familiar to the consumer
• Expectation of poorer performance of bio-materials in functional products (at least in the case of early developed products)
• Recycling of certain, new bio-products may require an infrastructure and capital investment. As incorporation with currently recycled petroleum-based materials is difficult

Even with these disadvantages, there is an increased incentive to use and produce materials obtained from renewable resources.Bio-based chemical building blocks are currently a fast developing for two main reasons: 
 

• The relatively high and variable cost of petroleum feedstock, and
• The environmental consequences of using petrochemical feedstock

However, these are both defensive positions. If the economic and environmental problems associated with petroleum-based feedstock would go away (a highly unlikely event), there would be little demand for bio-based chemical products. The recent drop in oil prices from their 2008 highs and the use of renewable feedstock for gasoline substitutes has somewhat dampened the enthusiasm for bio-materials in adhesives and sealants.
 

Modern-day adhesives are often fairly complex formulations of components that perform specialty functions. Very few polymers are used without the addition of some modifying substance such as plasticizer, tackifier, or inert filler. The selection of the actual ingredients will depend on:
 

• End-properties required
• Application and processing requirements, and
• Overall cost target of the adhesive

 The various components that can constitute an adhesive formulation include those shown in the table below:
 

Although substitution of the base polymer or binder with a material based on renewable sources will improve environmental impact, there are many other components in an adhesive system that can still detract from it being ultimately 'environmentally friendly'. Many of these additives are low molecular weight petroleum-based compounds. These could migrate out of the adhesive during its service life. 

Plasticizers, flame retardants, biocides, etc. have now come under considerable scrutiny. As they have been found in water sources and possibly could be detrimental to human health. As a result, there is significant effort going into the development of adhesives that have environmentally friendly additives as well as base polymers.

In an age of increasing environmental concerns, many of the tools that formulators had utilized in the past are no longer acceptable. Use of solvents has drastically been curtailed. Plasticizers must often be used in limited amounts. Regional regulations place demands that total VOC emission be kept to a minimum. Certain catalysts and additives are discouraged because of safety or health issues. 
 

Tables below provide examples of bio-based monomers / oligomers and polymers that are included in the SpecialChem adhesives master catalog.
 

The bio-content of these products ranges from about 30 percent to 100 percent. Much of the bio-based chemical building blocks are going into the high-volume plastic markets for obvious commercial reasons. However, the products listed in these tables have found acceptance in the adhesive markets. 

Today, bio-based polymers for adhesive formulations include primarily those based on soy and other vegetable products. However, this landscape is likely to change considerably in the future due to the customer's desire for bio-based adhesives. Even for those having less than 100% bio-content.

Previously, the following have been described:

The development and use of bio-based polyols are, in fact, not a recent occurrence. In sealants, especially, castor oil polyols have been used to provide good hydrophobicity and low moisture vapor transmission rate. The major barriers to the widespread acceptance of these raw materials are their availability and the cost to produce them.

 

• Polyols made from soybean oil are beginning to be used as partial substitutes for petroleum-based polyols. It has been noted that soy-based polyols do not have the high functionality and other properties to compete head-on as direct substitutes. However, they are increasingly becoming economically competitive as costs for competing petrochemical polyols rise.
   
• The use of soybean protein in water dispersed adhesives. Principally to replace formaldehyde adhesives in wood composites and panels²

These applications make up the majority of the current opportunities for soy in bio-based adhesives.

 

Both the triglycerides and the free fatty acids in vegetable oil such as soy can be epoxidized. These can find application in higher value products such as:
 

• Composites
• Adhesives, and
• Plasticizers
   

The major feedstock for this conversion is vegetable oil. Epoxidized oil is used mainly as a biodegradable plasticizer for adhesives and plastics. But, it also can be made part of a flexible epoxy resin molecule.

 

Bio-based Polyamides in Adhesives

Polyamides represent important products in various types of adhesive systems. They are used as hot melts and as modifiers and curing agents with epoxy resins. Several developments have focused on manufacturing polyamides from renewable sources. Potential market opportunities include:
 

• Textile interlining
• Technical textiles
• Building and construction
• Electronics, and
• Automotive

Following is the list of bio-based products by top Suppliers:
 

• Evonik Industries (Germany) has added a group of biobased polyamides to its Vestamid product line. These are based on monomers produced partly or entirely from fatty acids. The most important source is currently castor oil.
• Evonik is also forging ahead with the development of semi-crystalline polyamides . These are distinguished by high mechanical strength and good resistance to chemicals and stress cracking.
• Another new bio-based product is Platamid Renew from Arkema. This is a high-performance thermoplastic hot melt adhesive. It is produced from 100% vegetable oil developed for highly demanding and durable applications. The product can be processed into web, film, and filament using standard conditions and equipment.

There is significant effort going into the development of green adhesives. These have environmentally friendly additives as well as base polymers. The major 'green' adhesive additives are the subject of this section. The focus will be on the higher volume additives that are used in adhesive formulations. Replacement of lesser used hazardous materials such as flame retardants, biocides, etc. is well covered in the scientific literature. This relates to more specialty adhesive products.^3,4

Table below provides examples of bio-based adhesive additives that are included in the SpecialChem adhesives master catalog. The biocontent of these products ranges from about 30 percent to 100 percent. 
 

In recent years, environmentally safe or 'green' solvents have appeared on the market. They can provide alternatives for conventional solvents when regulatory, environmental, or safety and health pressures are exerted. Many of these solvents are based on agricultural or 'bio-based' feedstock. As such, they not only provide environmental benefit from their use, but they also avoid the more costly petroleum-based route to production. Several of the more common green solvents that have recently been commercialized include ethyl lactate, d-limonene, and methyl soyate. 

There is an increasing desire to develop plasticizers based on renewable raw materials. Compared to current petroleum derived polymers, these new products are expected to eventually offer:
 

• Reduced price
• Less price volatility, and
• A more favorable environmental footprint
   

They may also have certain application or performance properties discovered. This may further improve their commercial value.

 

Certain reports are coming to light that indicate that the bio-plasticizers may have functional attributes. These are of value and not available from current petroleum based products. It has been shown, for example, that one of the new bio-plasticizers (Reflex 100 from PolyOne having 94% bio-content) has significantly better performance properties compared to past industry standards, like:
 

• Thermal stability
• Lower plasticizer migration, and
• Improved plasticizer efficiency

Typical bio-polymers derived today from renewable sources generally lack elastomeric character. For example, renewable polymers such as polyhydroxyalkanoate or polylactic acids are not considered to have elastic characteristics and are noted for their:
 

• High degree of crystallinity
• High glass transition temperature, and
• Low elongation
   

As a result, most bio-polymers that are used in adhesive formulations require toughening agents or plasticizers to achieve greater flexibility.

 

Examples of natural product tackifiers are:
 

• Rosin acid derivatives and other esters.
• Another natural product is that based on a class of materials known as the terpenes. These tackifiers are extracted from pine trees and the paper production processes and then converted into resins. This is done with the help of distillation and further processing.
• Other, more modern bio-based tackifiers are based on citrus resources.

The adhesives industry represents a significant opportunity for the developing bio-polymers market. However, many obstacles must be overcome on the way to commercialization. To gain acceptance and supplant adhesive products derived from petroleum, industrial bio-polymers will need to be able to compete in terms of both cost and performance.

Advances in biotechnology and adhesive formulation will play a key role in surmounting these economic and technical barriers. By replacing conventional base polymer and property additives with bio-based products, formulators will project a 'green' image to companies. As they are increasingly interested in promoting their use of bio-based materials.