Promoting the Circular Economy Through Repulpability Testing of Coatings for Paper and Paint

Michelman is well known to possess expert materials knowledge and resources, which can be attributed to a compelling combination of world-class talent and specialty chemistries. These help customers around the world to excel in the diverse range of markets they serve with sustainable and responsible solutions.

A market leader in the development of barrier and functional coatings, as well as digital printing-press primers and OPVs that are used in the production of consumer and industrial packaging, paper products, labels, and commercially printed materials, they offer solutions that allow customers to make use of these products in a huge variety of end-use applications.

The coating solutions they have pioneered can improve sustainable practices that reduce waste, provide product protection and utilize fewer raw materials. They collaborate with members at every stage of the value chain including:

  • Paper Mills for paper evaluation and performance testing
  • Converters to develop new technology and customized structures
  • Brand Owners and Consumer Products Groups to design sustainable packaging solutions

Michelman developed the first water-based paper coatings and coatings applicators produced alongside each other as a total system to complement performance and have continued to improve paper’s performance and provide sustainability for both the businesses and in nature.

Their experts in the technical and market fields are encouraged to collaborate, resulting in innovations and product breakthroughs that lead to an accelerated concept-to-commercialization cycle.

Repulpable Water-based Coatings for Paper Packaging

Ever since their principle work on repulpable water-based coatings for corrugated paper packaging in 1963, thousands of packaging converters have used, recycled, and re-pulped hundreds of Michelman coating formulations. Michelman has demonstrated the repulpabilityof their products in the past using the TAPPI Method T205 (British disintegrator).

Environmental and Economic Benefits of Repulpable Coatings

With consumers now increasingly aware of the life cycle of packaging and its place in the circular economy (CE), the paper and packaging industry must realize the power of consumer choice and brand loyalty and reassess its relationship with waste, resources and material use. Michelman is setting the industry standard with novel coating technologies that facilitate CE principles of recovery, recycling, composting and repulpability.

Using repulpable coatings on paper and corrugated can bring about many environmental and financial benefits. Furthermore, the water-based chemistry Michelman applies as a coating is environmentally friendly, and enables recyclers to make a profit when purchasing the OCC (Old Corrugated Containers).This increases awareness of the benefits of the Circular Economy and eliminates further OCC being sentto landfills.

Michelman has sought out further validity in the repulpability of its coatings applied to linerboard with a stringent protocol established by a joint committee of the Fiber Box Association and the American Forest & Paper Association (see sidebar).This is a joint committee, representing manufacturers of container board, corrugated containers and others who use recovered corrugated container fiber.

Application of Michelman's Range of Repulpable Coatings

Michelman has successfully tested several of its coatings for repulpability, theyare described here along with their applications:

  • Michem® Coat 81 - A repulpable, printable, and cold set gluable coating optimized for water resistance and intermediate MVTR protection. Common uses include packaging for produce and meats, or anywhere packaged goods require protection from water or moisture vapor.
  • Michem® Coat 40EAF - A wax replacement coating that provides water resistance and some grease resistance that is typically used on fruit, vegetable and protein/meat boxes.
  • Nomar® 73 - A water-based, abrasion resistant coating generally used to provide abrasion protection for gas flushed food packaging or small appliances.
  • Coating X300AF™ - A coating that is also water-based that provides a high level of water and moisture resistance on Kraft paper. It protects food products from excessive moisture, freezer burn and sticking.
  • MaxWhite® 17 –A decorative white coating that provides excellent brightness before and after wax applications.

Surface Modifiers for the Paint and Coatings Industries

Michelman is also promoting the CE in the paint and coatings industries with technology helps manufacturers eliminate solvents and reduce VOCs. Their chemicals arm works with almost every type of wax and wax-like polymer currently used, and formulators have used Michem® surface modifiers to meet a multitude of objectives in paint and coating formulations including:

  • Stopping water penetration into wood and concrete
  • Adding scratch and mar resistance to plastic
  • Producing desired wood and metal finishes
  • Creating special effects such as soft feel and gloss matting
  • Controlling lubricity for high speed processing and rough service protection
  • Eliminating blocking in trim paints

Across the Paper & Corrugated, and Paint & Coatings industries, Michelman makes use of stringent testing procedures to allow its customers to meet sustainability and compliance goals, as well as initiatives in R&D and product development.

Repulpability Testing Procedure with Accordance to FBA Protocol

The Repulpability Testing Procedure followed by Michelman for every tested coating per the FBA protocol is entitled "Voluntary Standard for Repulping and Recycling Corrugated Fiberboard Treated to Improve Its Performance in the Presence of Water and Water Vapor."

The samples used for testing were sheets of 42 lb. linerboard coated with a variety of Michelman coatings.*

Step 1 - Cut board into 1¼" (31.8 mm) by 4" (102 mm) strips.

Step 2 - Weigh out 0.55 lb. (25 g) of board.
Michelman note: This weight measurement must exclude moisture content using the following calculation (assume moisture content is 7%):
100% - 7% = 93%
25 g = 0.93(x)
26.9 = x
Conclusion: 26.9 grams of sample must be used for the test.

Step 3 - Place the sample in 1500 mL of 125 °F ± 10 °F (52 °C ± 3 °C).
Michelman note: Water should have a pH of 7.0. and hot tap water provides the correct temperature. Use sulfuric acid to lower the pH to the correct level.

Step 4 - Preheat a modified one-gallon Waring blender (equipped with special blades) to 125 °F ± 10 °F (52 °C ± 3 °C).
Michelman note: Preheat the blender by running it under the same hot tap water used in Step 3.

Modified Waring blender

Modified Waring blender

Step 5 - Blend the sample in the Waring blender at 15,000 rpm (low speed) for four minutes.
Michelman note: We recommend holding the blender firmly in place at the beginning and throughout the cycle.

Special blades in Waring blender

Special blades in Waring blender

Step 6 -Rinse all remaining fibers from the blender with 500 mL of hot water.
Michelman note: Pour the mixture from the Waring blender into a British Disintegrator, also heated to 125 °F ± 10 °F (52 °C ± 3 °C).

Water running into the slotted, open screen box.

Water running into the slotted, open screen box.

Step 7 - Deflake for five minutes in the British Disintegrator (2000 ml total volume) at 3000 rpm.

Step 8 - Run the mixture on a 0.010 in. (0.254 mm) slotted open flat screen, maintaining a 1" water head for 20 minutes. Save the Accepts and Rejects in aluminum weighing pans.

Michelman notes: The fibers that pass through the screen are the “Accepts" and the fibers that accumulate on top of the screen are the "Rejects".

To start the flow of water into the screener box, the water escape is first closed, and then the flow for water entry opened, flooding the screen with water. Once the 1" (minimum) water head is achieved, the water escape flow is opened, and the water entry flow is increased to equilibrate the system. Once the 1" water head is consistently maintained, the pulp mixture from the British Disintegrator is poured onto the screen. Ordinary tap water can be used to rinse the disintegrator canister and capture all of the mixture.

When adding the pulp, the flow through the water escape will slow and the water head will begin to rise. To compensate, the flow of water from the water entry will also need to slow. Flow rates of the entry and escape hoses should be monitored and adjusted as necessary during the 20-minute period to maintain the minimum 1" water head.

As the test runs, water and some of the paper fiber will filter cleanly through the screen. This mixture is expelled through the water escape tube, with the fibers being captured in a sieve. The Rejects will accumulate on top of the screen and not pass through to the collection sieve.

When 20 minutes has elapsed, the flow of water from the water entry is stopped, and the screen is entirely drained. The Accepts are then removed from the sieve, scraping and using tap water to rinse (if necessary) to completely collect all material. The Accepts can be hand wrung if necessary to remove any excess moisture, and are placed in a previously tared beaker for drying. Additionally, the Rejects are removed from the screen using a scraper and placed in a previously tared beaker.

The Screen Box above shows water entry and water escape with shut-off valve. Pictured in the background is the Drying Oven (green).

The Screen Box above shows water entry and water escape with shut-off valve. Pictured in the background is the Drying Oven (green).

Step 9 - Dry in a laboratory oven for 12 hours (± 4 hours) at 221 °F (105 °C).

Step 10 - Weigh the samples and record the net weights of the Accepts and Rejects. The equation below determines the percentage Rejects.

The sample passes if the percentage of Rejects is less than 15% rounded to the nearest 0.1%

* Before beginning the Repulpability Testing Procedure, measure the treated sample’s moisture content as a percentage. Samples must be tested at least three times and pass two out of three tests.

This information has been sourced, reviewed and adapted from materials provided by Michelman.

For more information on this source, please visit Michelman.

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