This invention relates to the composition of matter of a polymer made from α-hydroxycarbonyl compounds (alpha-hydroxycarbonyl compounds), particularly α-hydroxyaldehydes (alpha-hydroxyaldehydes) and α-hydroxyketones (alpha-hydroxyketones) and more particularly from glycolaldehyde; optionally, the α-hydroxycarbonyl compounds are derived from renewable sources. This invention also relates to the methods for making the polymer.
As the plastics industry moves more toward bio-based products and raw materials, there is a need for high-performance renewable polymers. There is a lack of high performance polymers that can be made from bio-based, renewable sources.
A few examples of the very numerous manufactured items that substantially use petroleum-based polymers include water bottles, food packaging, durable goods such as wireless devices and agricultural films. Other examples of manufactured items that are made mostly from petroleum-based polymers include plastic utensils, cutlery and tableware, and these applications require a higher modulus (more rigid) thermoplastic polymer. A renewable polymer material would be useful for these and other manufactured items.
Current renewable polymers can be categorized into three classes. The first class includes nature-made polymers such as starch, cellulose, lignin, chitin, etc. that are transformed and processed into plastics and composites. Materials made from these sources have good degradation profiles and are often cost-competitive for disposable packaging applications, but their mechanical properties and processing characteristics are significantly inferior to engineered thermoplastics made from petrochemicals. The second class includes hybrid materials made by reaction of a renewable component with a petrochemical component; for example polyurethane coatings or foams can be made by reacting soy or castor oil polyols with a petrochemical di-isocyanate. This second class of material is only partially “renewable” and most products are thermosets rather than thermoplastics. The third class of renewable polymers is that of synthetic polymers made from renewable building blocks. This third class of renewable polymers offers, in principle, high versatility for making a variety of materials with different properties and performances. However, the choice for available renewable building blocks is extremely limited when compared to petrochemical monomers. Current renewable monomers include ethylene (from bioethanol) for making poly(ethylene), vegetable based polyols, diacids (such as succinic acid) and various hydroxy acids (or their cyclic lactones) such as lactic acid, glycolic acid, hydroxybutyric acid, and hydroxyvaleric acid for making polyesters. Therefore, current synthetic renewable thermoplastics are effectively limited to polyethylene and polyesters.
In another technology area, fast pyrolysis is one of the thermal processes that are being developed to make biofuels and bio-chemicals from biomass: it produces a liquid that can be used both as fuel and a source of chemicals. Fast pyrolysis is used on a small scale for producing glycolaldehyde and other hydroxyaldehydes for food applications and bio-lime as a sulfur oxide sorbent (Bridgewater 2004). Bridgewater (2004) teaches the above fast pyrolysis processes, and is incorporated by reference herein. One of the light components is 2-hydroxyacetaldehyde (also called “glycolaldehyde”). Depending upon the pyrolysis conditions and the feedstock, glycolaldehyde can constitute up to 17 wt %. of the bio-oil, and this fraction can be increased to 33% with the addition of sodium chloride (Bridgewater 1996). Glycolaldehyde spontaneously dimerizes to form the cyclic compound 2,5-dihydroxy-1,4-dioxane (DHDO). DHDO crystallizes to a white solid and therefore can be isolated in a highly pure form even when produced from a mixed feedstock and in the presence of other byproducts. Scheme 1 shows the spontaneous dimerization of glycolaldehyde in solution to form the crystalline cyclic compound 2,5-dihydroxy-1,4-dioxane (DHDO); the asterisks show the position of the chiral centers.

Kobayashi (1979) and Yaylayan (1998) teach that when glycoaldehyde is dissolved in water or solvents the 1,4-dioxane ring structure can reversibly open and close with the formation of up to nine different molecular species. Kobayashi, 1979 and Yaylayan, 1998 are incorporated by reference herein.
Glycolaldehyde is a two-carbon molecule, is non-toxic and is a natural metabolite resulting from the metabolism of sorbitol (a common low-calorie sweetener) and from the oxidative degradation of ascorbate and xylitol (O'Brien 2005). Glycolaldehyde is used in the food industry as a browning agent for baked goods, it is contained in soy sauce, and is formed naturally during sugar caramelizing.
Pyrolysis is the thermal decomposition in absence of oxygen. Fast pyrolysis is carried out by exposing finely subdivided (less than 3 mm in size) solid biomass (especially lignocellulosic feedstock) to high temperatures (400-500° C.) for a short period of time (for example, 2 seconds) in an inert atmosphere or under vacuum. This process produces a mixture of volatile gases, liquid vapors and aerosols. The mixture of products is then rapidly condensed to produce a brown dense liquid (bio-oil) which is about 50%-75% of the original mass and typically contains 15-35% water and a variety of oxygenated organic compounds including acids, phenols, and hydroxyaldehydes. Among the organic compounds glycolaldehyde is the most abundant component, 10-17% of the total depending upon the feedstock (Stradal 1993, Bridgewater 2005). A higher yield of glycolaldehyde can be obtained when using a feedstock that contains a high amount of cellulose or hemicellulose and less lignin. Glycoaldehyde is an example of a larger set of compounds known as α-hydroxycarbonyl compounds.
U.S. Pat. No. 5,252,188 (Stradal and Underwood, 1993) teaches a process to isolate or purify glycolaldehyde (2-hydroxyacetaldehyde) from pyrolysis-derived bio-oil. U.S. Pat. No. 5,252,188 is incorporated by reference herein. Majerski (2001) teaches a method for isolation of glycolaldehyde based on the crystallization of its dimeric form (U.S. Pat. No. 7,094,932).
There remains a need in the art for polymers that can be obtained from bio-derived feedstocks. This invention teaches the composition and methods of preparation of novel renewable thermoplastic polymers made from hydroxyaldehydes, which may optionally be derived from the fast pyrolysis of biomass, specifically cellulosic feedstock. Thermosets are polymers that form irreversible bonds during cure, while thermoplastics are polymers that become pliable or moldable above a specific temperature and return to a solid state upon cooling. There is a particular need in the art for renewable thermoplastics.