Better Adhesives Mean Stronger, Cheaper Wood Products

(This article was originally posted on Inside the Forest Service.)

As great as engineered wood—such as plywood or particle board—is for a range of building and manufacturing uses, it has its limitations, especially in outdoor applications. One of the biggest limitations is not the wood, but the adhesive used to glue the wood veneers or particles together. In the United States, the most commonly used adhesive in outdoor engineered wood products is phenol-formaldehyde resin.

To accelerate development of new and improved wood adhesives for engineered wood products, Forest Service researchers Joseph Jakes, Chris Hunt, Nayomi Plaza, Dan Yelle, Chuck Frihart and Linda Lorenz, along with collaborators at Oregon State University, Argonne National Laboratory and Scion, a New Zealand research lab, are working to understand the optimal adhesive penetration into wood for specific products and applications. They want to know what controls performance at the bond line—where the adhesive meets the wood.

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A Golden Achievement

Linda Lorenz, a chemist at the Forest Products Laboratory (FPL), is celebrating an incredible 50 years of service to the Federal government this year. Amazingly, every one of those years was spent right here at the Lab.

Linda Lorenz (right) accepts her 50 years of service certificate from Acting Director Tony Ferguson.

Linda Lorenz (right) accepts her 50 years of service certificate from Acting Director Tony Ferguson.

“I have enjoyed working at FPL and being a part of the great research that is done here, because I have the challenge of helping to solve problems with chemistry,” Lorenz said.

While she has held several different positions and worked on various projects over the past five decades, currently Lorenz is studying wood adhesives in the Forest Biopolymer Science and Engineering research work unit.  She also regularly coordinates FPL’s robust volunteer and fundraising efforts.

Lorenz was honored this week along with many colleagues during FPL’s annual Length of Service ceremony.

Congratulations, Linda, and (since there is no talk of retirement, yet) keep up the good work!

 

 

Cellulose Nanocrystals as Filler for Polymers

In a new publication, Supervisory Research Materials Engineer Gregory T. Schueneman reports on his research with cellulose nanocrystals (CNCs). CNCs are a class of renewable bionanomaterials with excellent mechanical properties that have attracted interest as filler for polymers. However, challenges associated with effective CNC dispersion have hindered the production of composites with desired property enhancements.

In Schueneman’s research, composites of polypropylene (PP) and low-density polyethylene (LDPE) with 5–10 wt% unmodified CNC are being produced for the first time with a solventless process, solid-state shear pulverization. Optical and electron microscopy revealed that the CNC dispersed very well and that degradation was strongly suppressed relative to composites made by melt mixing.

Field emission (FE) scanning electron microscope (SEM) images of as-received CNC at different weights.

Field emission (FE) scanning electron microscope (SEM) images of as-received CNC at different weights.

Taking thermal stability into account, this study has produced polyolefin/CNC composites with superior dispersion and property enhancements and has shown that CNC is an attractive and green filler for polymer composites. Over 50 million tons of plastic resins are used annually in the United States to manufacture products for a variety of end uses, including packaging, building materials, vehicles, furniture and furnishings, and electronics and electrical devices.

In this study, solid-state shear pulverization was used for the first time to produce composites of polyolefins and unmodified CNC. Microscopy and improved crystallization rate reveal excellent dispersion and suppression of CNC degradation within the polymer compared with composites made by melt mixing.These composites exhibit substantially greater stiffness, the greatest improvement ever reported for such composites made with unmodified CNC.

This study showed that CNC is an attractive and green filler for polymer composites.

The publication, titled “Cellulose nanocrystal/polyolefin biocomposites prepared by solid-state shear pulverization: Superior dispersion leading to synergistic property enhancements,” will be available online shortly. Cooperators include the USDA Forest Service Forest Products Laboratory, Madison, Wisconsin, and Northwestern University, Evanston, Illinois.

Set Free the Cellulose! Enhancing Biorefinery Economics through Ionic Liquid Pretreatment

As the most abundant biopolymers on earth, cellulose and lignin form the building blocks for trees and other plants. For centuries the durable, renewable benefits of wood have helped provide shelter and energy for people across the globe. Using trees such as Loblolly pine and other lignocellulosic biomass like wheat straw and Miscanthus – as renewable, plentiful, non-food and non-petroleum resources – can help reduce dependence on oil products by supplementing traditional gasoline supplies with liquid biofuels.

Yelle

Daniel Yelle, a research forest products technologist at FPL

One of the biggest challenges of converting wood-to-energy is releasing the sugars within the lignin itself. Daniel Yelle, a research forest products technologist at the Forest Products Laboratory says lignin is recalcitrant, meaning it does not break down very easily. Yelle has been working with a team of researchers to unlock the recalcitrant nature of lignin in an effort to improve refinery efficiencies in the production process for advanced biofuels. Their research has been published in the scientific journal Green Chemistry.

Higher plants such as trees, says Yelle, contain cell walls that are rich in lignin and complex sugars – polysaccharides like cellulose. However, cellulose is naturally entrapped in a matrix of lignin. Cellulose is the ideal biopolymer for biofuel production, says Yelle, “because of its simplistic long-chain glucose structure” but the separation of the cellulose from its lignin counterpart typically involves harsh chemical pretreatments. These chemicals may release the cellulose to a certain degree but, says Yelle, “make the remaining lignin even more recalcitrant.” Overcoming pretreatment barriers would help make the biochemical conversion process more efficient and thus more appealing for commercial renewable energy interests.

Yelle and colleagues’ research analyzes lignin following an ionic liquid pretreatment. Ionic liquids, says Yelle, are used to more easily dissolve the lignin that directly surrounds the desired polysaccharides. The non-toxic and recyclable ionic liquid used in this study, says Yelle, was able to more effectively disrupt the lignin, allowing for its extraction in a more native-state, as compared to previous pretreatment strategies. The subsequent use of enzymes to breakdown the polysaccharides into simple sugars is thus more effective. Furthermore, says Yelle, the size of the lignin polymer that is removed can be customized and routed into different product streams and help improve biorefinery economics.

LigninPretreatment_Yelle_4web

Above, a representation of the ionic liquid pretreatment process for converting biomass to sugars suitable for manufacturing liquid biofuels.

Soy Proteins as Wood Adhesives

Protein-based adhesives have a long and ingenious history. Animal protein, casein from milk, soy flour, and even blood have historically been used as bonding agents for wood product applications. These proteins have allowed for the development of bonded wood products such as plywood and glued-laminated timbers in the early 20th century.

Beam-installation-in-blg-2_4web

Casein proteins from milk were used to make glued-laminated arches, seen here in the construction of the former Building Two at FPL (1930s).

Petrochemical-based adhesives replaced proteins in most wood bonding applications because of lower cost, improved production efficiencies, and enhanced durability. Technological and environmental factors, however, have led to a resurgence of proteins, especially soy flour, as an important adhesive for interior nonstructural wood products. Among other factors, more stringent regulations limiting formaldehyde emissions from composite and wood panels have driven renewed interest in soy adhesive technology.

Charles Frihart and Christopher G. Hunt, both Forest Biopolymer Science and Engineering chemists at FPL, along with co-author Michael Birkeland, of AgriChemical Technologies, describe the value of soy proteins as wood adhesives in a chapter of Recent Advances in Adhesion Science and Technology (Gutowski & Dodiuk, eds.).

Their paper discusses important aspects of protein structure and recent successful advances in higher performance soy flour adhesives for wood bonding. Protein wood adhesives have recently displaced fossil fuel-based adhesives in some markets and have the potential to replace a significant percentage of fossil fuel-based wood adhesives worldwide.