TABLE OF CONTENTS

Introduction CONSIDERING COATINGS THROUGH A CHIP PACKET 2

Chapter 1 BETTER BARRICADES TO OXYGEN 3

Chapter 2 PACKAGING WITH A PRETTY FACE 5

Chapter 3 STICKING TO THE TASK 7

1 CONSIDERING COATINGS THROUGH A POTATO CHIP PACKET

hen it comes to coatings, you may The properties of colloidal silica provide many not immediately think of a bag of opportunities to improve such packaging. potato chips. But a potato chip bag It consists of spherical nanoscale particles, Whappens to be one of the applications that which are known to be nontoxic. Their most effectively highlights the diverse ways extreme hardness helps keep chip packaging in which colloidal silica–based coatings can rolling smoothly along the production line. improve product performance. Covering each particle’s surface are silanol groups, which can bond strongly to a range Such packaging might simply be thought of as of materials, from polar polymers in the something destined to be scrunched up and packaging to the vibrant inks that tantalize thrown into the trash at the end of the . consumers. Because of their small size, silica But packaging potato chips is a technically nanoparticles don’t alter the packaging’s demanding challenge, and the chip bag is a appearance. When you consider that colloidal sophisticated multilayer product. silica has been approved for food-contact applications, the deal is sealed. The packaging must retain a pleasing look from the manufacturing facility to the grocery My colleagues and I at W. R. Grace & Co. hope store and ultimately to the consumer. It that you enjoy this fascinating exploration of the also must protect the contents from oxygen chemistry of potato chip packaging. Although and moisture—which can lead to product the potato chip bag is just one example of a degradation or spoilage—for the shelf coated material, we hope that you agree it life of the chips, typically 3 to 4 months. offers a brilliant example of colloidal silica’s key The packaging must also be lightweight, properties at work. inexpensive, and durable.

As the following chapters outline, LUDOX® colloidal silica is the idea partner to enhance the performance of coatings for chip packaging. Steve Broadwater, PhD Lead Technical Service Manager, Americas W. R. Grace & Co.

2 BETTER BARRICADES TO OXYGEN

The material at the core of most chip packaging is usually a polyolefin film. SHUTTERSTOCK

iting into a potato chip is a multisensory downsides: their glossy surface is difficult to experience. The anticipation triggered print on and they are easily penetrated by by seeing the golden chip and lifting oxygen. To overcome these limitations, several Bit from the packet, the tantalizing aroma, the coating layers are usually applied. satisfying crunch, and then the hit of flavor on the tongue, engages all five senses. To keep out oxygen, the barrier properties of chip packaging have traditionally been en- Ensuring that each potato chip satisfies all the hanced with the application of a thin coating of senses is a key role of the packaging. As with metal, such as aluminum, creating the shiny much , chip packaging is a surface on the inside of the packet. “But the sophisticated, multilayered material designed to trend is to get rid of aluminum,” says Cagri look good and to keep the product inside fresh Üzüm, technical customer service manager at and safe, in perfect condition for consumption. Grace GmbH. Because it is harder to recycle, plastic packaging with metal film coatings is en- For almost any food product, the main ene- vironmentally undesirable. In addition, the metal mies to quality and freshness are oxygen and film makes the packaging opaque and prevents 1 moisture, says Marlene Cran, a food-packaging customers from seeing the product inside. materials researcher at Victoria University in . The two cause food spoilage through Food-packaging researchers are exploring oxidation reactions and by promoting microor- nanotechnology to boost the barrier prop- ganism growth. The packaging for the potato erties of food-packaging polymers without chips is a critical barrier to the action of oxygen metal films.1 The approaches being explored and moisture and prevents potato chips from include packaging materials that incorporate going stale, discoloring, or developing off-fla- colloidal silica nanoparticles to improve gas vors and aromas. barrier performance. These nanoparticles are approved for applications in which they con- The material at the core of most chip packaging tact food and have been shown not to migrate 2 is usually a polyolefin film, such as bi-oriented from food-packaging polymers into food. polypropylene (BOPP). Polyolefins’ attributes “Colloidal silica is an intriguing material for include excellent transparency; an attractive, food packaging applications,” says Loong-Tak glossy appearance; and good moisture-bar- Lim, a faculty member with the department of rier properties. Polyolefins also have a few food science at the University of Guelph.

3 “The idea of silica particles strengthening the particularly well with polar polymer matrices. A polymer network they are dispersed in has been mixture of colloidal silica and a polar polymer around a long time,” says David Chapman, a can be used as a coating to enhance the research fellow at W. R. Grace & Co. In 1941, barrier properties of common food packaging researchers discovered that adding silica polymers like BOPP. nanoparticles to natural rubber improved the wear resistance of vehicle tires. “The concept For example, researchers led by Stefano of adding silica nanoparticles to food-packaging Farris at the University of Milan recently polymers is basically the same,” Chapman says. showed that colloidal silica enhanced the barrier properties of coatings based on pul- Colloidal silica is a nanoparticulate form of lulan, an environmentally friendly biopolymer silicon dioxide, so its interactions are dominat- obtained via yeast fermentation.3 Oxygen ed by the polar silanol groups that cover its barrier properties were particularly enhanced surface. Polyolefin films destined to become using nanoparticles with the highest surface chip packaging can readily be coated with polar area. The key mechanism involved was the polymers that have been blended with colloidal nanoparticles’ strong bond to the pullulan silica nanoparticles to help block oxygen’s path. polymer chains. The strong interactions increased the polymer’s density and restrict- Silica nanoparticles in the coating can slow ed each chain’s mobility to significantly slow oxygen molecules moving through the materi- oxygen’s passage through the material. al in two ways. First, the nanoparticles within the polymer matrix act as a physical imped- In a 2016 publication that described this work3, iment to gas molecules passing through the Farris and his colleagues concluded, “The packaging, complicating the gas’s path and addition of colloidal silica nanoparticles to the slowing its passage. Second, nanoparticles main pullulan coating laid on the BOPP film is can improve gas barrier performance by an effective strategy for improving the overall influencing the surrounding polymer chains. performance of the final food-packaging With very high surface area relative to mass, material.” This sort of innovation may satisfy small particles like colloidal silica offer a huge not only chip lovers’ basic five senses but, interfacial surface, Chapman notes. “If the by offering a strategy to remove metals from forces between polymer and silica are strong, chip packaging, their sense of environmental that completely changes the properties of the responsibility as well. polymer,” Chapman says. “Strong interaction tends to distort and densify the polymer, and 1. Cesare Rovera, Masoud Ghaani, and Stefano Farris, “Nano-Inspired Oxygen Barrier Coatings for Food Packaging Applications: An overview,” Trends Food Sci. that can also help lower the diffusivity of the Technol., 97 (March 2020): 210–220, doi.org/10.1016/j.tifs.2020.01.024. gas through the film.” 2. Johannes Bott, Angela Störmer, and Roland Franz, “Investigation into the The nature of the particle-polymer interface is Migration Potential of Colloidal Silica from Food Packaging Plastics into Food” (paper presented at the Innovations in Food Packaging, Shelf Life and Food the most critical for the performance of barrier Safety Conference, Erding, Germany, Sept. 15–17, 2015). coatings, Lim says. “If you have a strong inter- action between the polymer and the dispersed 3. Carlo A. Cozzolino et al., “Influence of Colloidal Silica Nanoparticles on Pullulan- particles, now you see the reinforcement.” Coated BOPP Film, Food Packaging and Shelf Life (June 2016): 50–55, doi. Colloidal silica’s silanol groups interact org/10.1016/j.fpsl.2016.03.003.

4 PACKAGING WITH A PRETTY FACE

SHUTTERSTOCK

he consumer’s first interaction with a po- surface, dry quickly enough to lock each ink tato chip—long before biting into one—is droplet in place, and ensure a high-resolution the packaging. Its design and appear- and long-lasting printed surface.3 Tance, and the glimpses it offers of the product inside, are essential elements of consumer Silica has an excellent track record in en- choice and enjoyment. Food packaging can be hancing the printability of glossy surfaces. intimately tied to our experience of the product “Colloidal silica is used on high-quality, ® itself. When SUNCHIPS introduced packaging high-gloss photography paper to increase that was compostable but made a loud crinkling printability,” says Cagri Üzüm, a technical sound when handled that just didn’t sound like customer service manager at Grace GmbH. a chip packet usually did, consumers stopped Colloidal silica even seems to enhance the 1 buying the brand. And a group of researchers color reproduction of coated photo paper, ac- demonstrated in a 2019 publication that chang- cording to David Chapman, a research fellow ing the design of food packaging can affect how at W. R. Grace & Co. who formerly worked on highly consumers rate their enjoyment of the porous silica gels as coatings for inkjet paper. 2 product’s taste. “Looking at the color gamut, we were never really able to pin down the mechanism,” The vibrant, colorful designs typical of potato Chapman recalls. “But it always seemed chip packaging are key to the product’s ap- the colors were a little bit more vibrant when peal. But printing these designs onto the thin printed on silica.” polymer films that compose the packaging can be a challenge. The smooth, nonporous, Colloidal silica’s printability-enhancing prop- hydrophobic polyolefin films typically used erties can also be applied to food-packaging for food packaging have poor compatibility materials. “Instead of an ink laying down on a with water-based inks. Printing directly on the nonpolar polyolefin surface, now you’ve got an films will not achieve a high-quality appear- ink laying down on colloidal silica,” Chapman ance, so other strategies must be used. says. “That’s a very different chemistry.” The key functional feature of unmodified colloidal The key to printing on chip packaging is silica is that its surface is covered with silanol covering the polymer film with a coating that groups, silicon’s equivalent to hydroxyl groups. enhances its wettability toward the ink. A The silanol groups “love to interact with other coating has to rapidly draw the ink onto the hydroxyl groups or polar functionalities in

5 organic molecules. They love to hydrogen University in Australia who has investigated bond,” Chapman says. “The silica will interact the optical clarity of nanomaterial-reinforced with dye-based materials and give them some biopolymers.5 Researchers have shown that permanence.” Although individual colloidal silica silica nanoparticle coatings can be ideal in particles are hard and nonporous, a coating that this scenario, significantly enhancing gas incorporates colloidal silica can feature pores barrier performance without degrading optical between the spherical particles, and the pores transmittance.6 improve ink uptake. Colloidal silica makes a long-lasting contribution Researchers in Italy recently demonstrated to the attractiveness of food packaging. Thanks colloidal silica’s potential to improve the print- to silica particles’ hardness, their networks can ability of food packaging. The team coated make a coated surface resistant to scratches bi-oriented polypropylene (BOPP) food pack- and abrasion.7 This is just one more way that aging with a combination of colloidal silica colloidal silica can help to ensure the chip and pullulan biopolymer, which improved packet remains vibrant from the manufacturing the packaging’s wettability, a key indicator of plant to store shelves to the hands of hungry printability.4 The results obtained with pullu- consumers drawn by the sight—and sound—of lan—a biopolymer widely investigated as a a good bag of potato chips. green material for food packaging—illustrate how colloidal silica could enhance the proper- 1. Suzanne Vranica, “Snack Attack: Chip Eaters Make Noise About a Crunchy Bag,” Wall Street Journal, August 18, 2010, sec. US Page One, https://www.wsj.com/ ties of many polymers for such packaging. articles/SB10001424052748703960004575427150103293906.

Significantly, the researchers reported that 2. Nadeesha M. Gunaratne et al., “Effects of Packaging Design on Sensory Liking adding colloidal silica to the pullulan coating and Willingness to Purchase: A Study Using Novel Chocolate Packaging, Heliyon 5, no. 6 (June 2019): e01696, doi.org/10.1016/j.heliyon.2019.e01696. did not alter the excellent optical clarity of the transparent polymer film. Although the colloi- 3. KazuhisaTsuji, Tomoki Maeda, and Atsushi Hotta, “Polymer Surface Modifications dal silica’s nanoparticles can favorably inter- by Coating,” Printing on Polymers: Fundamentals and Applications (2016): act with ink droplets, the particles themselves 143–60, doi.org/10.1016/B978-0-323-37468-2.00009-9. are too small to be seen by consumers. The particles have no direct impact on the optical 4. Carlo A. Cozzolino et al., “Influence of Colloidal Silica Nanoparticles on Pullulan- Coated BOPP Film,” Food Packaging and Shelf Life (June 2016): 50–55, doi. qualities of the packaging material. From org/10.1016/j.fpsl.2016.03.003. shiny, glossy, opaque packaging to trans- parent packaging, colloidal silica does not 5. Bakti B. Sedayu, Marlene J. Cran, and Stephen W. Bigger, “Improving the alter the packaging’s appearance or optical Moisture Barrier and Mechanical Properties of Semi-Refined Carrageenan Films, performance. J. Appl. Polym. Sci. 137, no. 41 (Nov. 5, 2020): 137, e49238, doi.org/10.1002/ app.49238.

With a move away from opaque, metallic 6. Gree Bang and Seong Woo Kim, “Biodegradable Poly(lactic Acid)-Based films in food packaging, chip packets are Hybrid Coating Materials for Food Packaging Films with Gas Barrier Properties,” starting to feature a window to the alluring J. Ind. Eng. Chem. 18, no. 3 (May 25, 2012): 1063¬68, doi.org/10.1016/j. jiec.2011.12.004. . “You don’t want something opaque and murky that your customers can’t see 7. Rojcharin Chantarachindawong et al., “Development of the Scratch Resistance through,” says Marlene Cran, a food-pack- on Acrylic Sheet with Basic Colloidal Silica (SiO2)—Methyltrimethoxysilane aging materials researcher at Victoria (MTMS) Nanocomposite Films by Sol–Gel Technique,” Can. J. Chem. Eng. 90, no. 4 (Aug. 2014): 888–96, doi.org/10.1002/cjce.21631.

6 STICKING TO THE TASK

To prevent polyolefin film from sticking to itself, anti-blocking agents are sprayed onto its surface prior to spinning the film into rolls. SHUTTERSTOCK

olloidal silica has a place on the potato filled with a dilute colloidal silica solution and chip package itself as well as a role dried before rolling. behind the scenes—in the chip packet Cmanufacturing plant. In addition to its potential to improve some of the functional properties and the appearance of potato chip packaging, “The antiblocking idea colloidal silica is also regularly used to keep the manufacturing process running smoothly. is to create a certain roughness so when two Polyolefin film is the backbone of packag- ing. As it spools out of the production ma- surfaces come together, chine, the polymer is collected in vast rolls, there is not such intimate ready for the next phase of the process. “As the polymer is rolled, it is still warm,” says contact between them.” Cagri Üzüm, a technical customer service — David Chapman manager at Grace GmbH. The layers at the bottom of the large roll are also pressed together by considerable weight. If nothing is done, Üzüm says, the plastic layers stick The thin silica layer provides antiblocking to each other—called blocking—and can’t properties by giving the surface of the be unrolled. polymer film a slight roughness on the na- noscale.1 Colloidal silica particles are hard To prevent blocking, the polyolefin gets a light spherical particles, akin to nanoscale glass spray of colloidal silica in aqueous solution beads. “The antiblocking idea is to create just before it is rolled. “The water evaporates a certain roughness so when two surfaces instantly, and what stays is just a very thin come together, there is not such intimate con- layer of silica,” Üzüm says. Alternatively, the tact between them,” says David Chapman, plastic film can be passed through a bath a research fellow at W. R. Grace & Co. The

7 Researchers have found In the packaging plant, the colloidal silica coating continues to offer benefits into the that the thin layer of last step of the process, when the finished, fully printed packaging is filled with potato colloidal silica applied chips and the packet is sealed. “This sealing for antiblocking has is done by heat treatment—by two hot metal plates pressing the plastic film to seal it,” additional benefits in food Üzüm says. There, he says, colloidal silica packaging. has two other roles.

First, as the plates press the softened plastic layers together, the silica nanoparticles on colloidal silica “is really acting like a physical either side of the join bind to each other and spacer between the two,” he adds. to the other components in the mix to help form a strong seal.2 Heating can induce con- The colloidal silica’s antiblocking effect is densation reactions between silanol groups so strong, it can prevent the large rolls of of neighboring silica nanoparticles and co- warm polymer food-packaging films from valently bond adjacent particles together to sticking. Other industries have also adopted enhance adhesion. colloidal silica for antiblocking, notes Steve Broadwater, the lead technical service man- Second, once the packaging is sealed, the ager in the Americas at W. R. Grace & Co. hot metal plates are separated. The silica “It’s often used in industrial wood coatings,” continues to contribute a nanoscale rough- he says. Colloidal silica can be formulated ness that acts as an antiblocking agent, into the top coat of paint used in the factory ensuring that the hot plastic doesn’t adhere to production of interior doors, for example. the plates. “Manufacturers may need to stack these freshly painted, oven-dried doors sometimes The sealed packages of chips are then sent 40–50 doors high while they are still warm, so off to grocery shelves. The seal holds until the they use colloidal silica to stop the doors from consumer rips it apart, plucks out a perfectly sticking together.” preserved potato chip, and takes the first satisfying crunch. Researchers have found that the thin layer of colloidal silica applied for antiblocking has ad- 1. Robert E Patterson, “Preparation and Uses of Silica Gels and Precipitated ditional benefits in food packaging. The coating Silicas,” Colloid Chemistry of Silica, vol. 234 of Advances in Chemistry series helps the polymer run smoothly through pack- (American Chemical Society, May 5, 1994): 618–26, DOI: 10.1021/ba-1994- 0234.ch032. aging machinery, preventing sticking whenever

it meets a hot surface, such as in the food-filling 2. Horatio E. Bergna and William O. Roberts, eds., Colloidal Silica: 2 machine. And researchers led by Stefano Fundamentals and Applications (Boca Raton, Florida: CRC Press, 2005) doi. Farris at the University of Milan recently found org/10.1201/9781420028706. that food-packaging coatings that incorporate colloidal silica can also reduce friction within the 3. Carlo A. Cozzolino et al., “Influence of Colloidal Silica Nanoparticles on Pullulan- Coated BOPP Film,” Food Packaging and Shelf Life (June 2016): 50–55, doi. machines, speeding up packaging operations org/10.1016/j.fpsl.2016.03.003. and enhancing throughput.3

8 WHAT IS YOUR LUDOX® COLLOIDAL SILICA CHALLENGE?

pecialty coatings, catalysts, zeolites, insulation board, refractory fibers, precision investment casting, paper and cardboard, flooring, beverages, concrete densifiers, polished concrete, textiles, or Selectronic components? Something entirely different?

Grace manufactures LUDOX® colloidal silicas in a broad range of particle sizes and surface modifications to deliver excellent performance in many different applications. Depending on your application—from medicine to manufacturing—and its potential in the marketplace, Grace can help you select or even customize the particle size and chemistry to make your idea work, or work better. Whether it becomes part of your product or a key to your process, LUDOX® colloidal silicas’ quality and consistency are renowned— and reliable.

Cited in over 30,000 patents, applications for LUDOX® colloidal silicas are numerous and diverse. As demonstrated in these case studies, researchers continue to discover new ways to use LUDOX® colloidal silicas in cutting- edge research, breaking ground for future scientific innovation and leading to potentially thousands more patents to come.

What can LUDOX® colloidal silicas do for you? Find out at grace.com/ludox

The case studies in this ebook are based on research conducted and compiled by C&EN Brandlab.

GRACE® and LUDOX® are trademarks, registered in the United States and/or other countries, of W. R. Grace & Co.-Conn. TALENT TECHNOLOGY TRUST™ is a trademark of W. R. Grace & Co.-Conn. SUNCHIPS® is a trademark registered in the United States and/or other countries of Frito-Lay North America, Inc. a Division of PepsiCo. This brochure/presentation is an independent publication and is not affiliated with, nor has it been authorized, sponsored, or otherwise approved by Victoria University in Australia, University of Guelph, and University of Milan. This trademark list has been compiled using available published information as of the publication date and may not accurately reflect current trademark ownership or status. © 2021 W. R. Grace & Co.-Conn. All rights reserved.

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