What’s comes into your mind when you hear the word ‘kraft paper’? For some people, it’s a thick brown paper used to pack lightweight things. For others, it’s just a fancy paper used in school projects.
With increasing concerns about environmental issues, people are shifting their loyalties to eco-conscious businesses and products. Kraft paper is one of those products. It has become popular over the years due to its environment-friendly design and qualities.
In this overview article, we’ve explained what components make kraft papers eco-friendly, how many types of kraft papers are there, and what they are used for. Let’s start with the basics.
What Is Kraft Paper?
Kraft paper is cardboard or a thick paper created from chemical pulp produced in the kraft process. It is strong, relatively coarse, and has high tensile strength.
The paper is named after the German word kraft, which means ‘strength,’ which refers to a particular pulping process that produces strong paper. This process was invented by a German chemist, Carl Ferdinand Dahl, in 1879.
The US Patent 296,935 was issued five years later, and the first kraft paper manufacturing company began in Sweden in 1890. The invention of the recovery boiler in the 1930s further enhanced the kraft process, making it more efficient and environment-friendly. By the mid-1940s, the kraft process became the most commonly used technique for producing wood pulp.
Unlike other papers, kraft paper can be created by using various types of wood and non-wood materials, including bamboo, resinous pine, and agri-residues. It contains highly oriented fibers that make it strong and durable.
Kraft papers, specially designed for packaging, have high elasticity and high tear resistance. They have a density between 40 and 123 g/m2. And since kraft wrapping papers are lightweight, they keep shipping costs low while offering better protection than many other packing materials.
Most Common Uses
Kraft papers are used for a broad range of applications across the world, for example,
- Paper sacks for consumer goods, food, flour bags, etc.
- Multiwall sacks
- Wrapping flower bouquets
- Corrugated layered cardboard
- Base of sandpaper
They are also used for making eco-friendly business cards and brand-printed brochures. Coated kraft paper, with high compression resistance and tear resistance, is often used in printing.
How Is It Made?
Kraft paper can be made by using hardwood, softwood, or even non-wood agri-residues. In the kraft process, the wood is converted into wood pulp, which contains pure cellulose fibers — the key component of the paper.
Initially, wood chips are treated with a hot mixture of sodium sulfide, sodium hydroxide, and water in large pressure vessels known as digesters. These vessels can hold up to 20 tons of pulp and support two types of processing: continuous and batch. The mixture breaks down the bonds that attach lignin, hemicellulose, and cellulose.
Since kraft pulping eliminates most of the lignin present naturally in wood, the pulp created in this process is stronger than that produced by other pulping methods.
Another major advantage of this process is that approximately 90% of the pulping chemicals can be recovered and reused without harming the environment. This makes the process both affordable and sustainable.
Some papers are eventually coated with polyethylene to make it more resistant to bacteria, moisture, and grease. Some are coated with zein (a class of prolamine protein) to make the paper water-resistant and preserve its recyclability.
Different Types Of Kraft Papers
Kraft papers can be categorized into two groups: unbleached and blanched ones.
1. Unbleached Kraft Papers
Unbleached or natural craft papers are the strongest of the common packaging papers and are used when maximum strength is required. They can be further categorized:
1.a) Virgin Natural Kraft Paper
It’s an inexpensive and durable kraft paper preferred in many applications due to its high strength and strong fibers. It features superior bursting strength, impressive tear resistance, and can contain up to 5% recycled materials.
It is mostly used for book covers, wrappers, carrier sheets, paint masking, stationery products, pallet interleaving, and floor protection liners. The paper can be printed on as well, which makes it perfect for branding.
1.b) Black Kraft Paper
Black kraft is a unique decorating tool mostly used in areas where dark borders and light barriers are required. Not only it gives a clean, professional look, but also provides a smooth surface texture, adding a glossy look.
These papers are commonly used in banners, bulletin boards, table coverings, and wrapping. They are also good for interesting craft projects.
Resilient to tears and punctures, these heavyweight papers are used for art projects, banners, table covering, and bulletin boards. They usually have duo-finish: the surface on the one side is smooth and ideal for finger painting and fine line drawing, while the other side has a textured surface for chalk and acrylic paints.
1.d) Recycled Kraft Paper
It is slightly weaker than virgin kraft due to its recycled fiber content. However, it costs less and is more eco-friendly. It also tends to have a softer feel and many beneficial qualities. For example, it is used for internal carton packaging, dust covers, newspaper bottom wrap, floor protection liners, and void filler or dunnage.
1.e) Foaming Kraft paper
Polyethylene foam roll laminated with high-quality kraft paper offers excellent chemical resistance. It has a high density, which prevents too much chemical penetration and works as an acoustic insulator. It also hides the material wrapped in it. These papers are often used in padded envelopes and bags, and they adapt to any shape and surface.
1.f) Sack Kraft Paper
These papers strike the perfect balance between porosity and strength. They have high tear resistance and high elasticity. They are perfect for valve sacks for commodities such as cement and other powdered materials.
Depending on the required toughness, multiple layers of sack papers can be used to make this kraft paper. It may also be coated with polyethylene to protect materials from moisture and bacteria.
1.g) Electrical Grade Insulation
Electrotechnical kraft is made by a unique cleaning method that involves the removal of charged ions and impurities from the pulp. It is specially designed for the insulation of transformers, bushings, high-voltage cables, and other electrical components.
1.h) Absorbent Kraft Paper
It has a high degree of porosity with good absorbency for resin impregnation. This type of kraft paper is used as a laboratory filter paper and a special bag for the plantation of saplings. It is also used in building and furniture construction where impregnated absorbent papers are pressed onto substrates such as plywood.
1.i) Printed Kraft Paper
Kraft papers can also be used to make super cool menus, greeting cards, and marketing materials. Krafts’ smooth brown tone adds a vintage look to any print. Much like recycled paper, it has an uncoated finish and a natural, textured appearance that gives it a tactile quality and makes ink appear flattered.
2. Bleached Kraft Papers
They are made by treating the natural kraft paper with bleach and other chemicals. This treatment makes the paper stronger and whiter. And because of this added strength and better appearance, bleached papers are extensively used in wrapping and packaging.
Apart from its impressive strength, white-bleached kraft paper is also recyclable, eco-friendly, durable, non-toxic, and aesthetically pleasing. Based on applications, it can be further divided into four groups.
2.a) Machine Glazed
Machine-glazed bleached kraft paper has a high gloss on one side of the paper, which makes the paper more opaque, printable, and durable. It is primarily used for food packaging, wrapping, industrial coating, and lamination.
2.b) Machine Finished
It is the most versatile kraft paper with high stiffness and plenty of commercial applications. These papers are commonly used in carrier bags, wrapping, aluminum foil lamination, and protective products.
2.c) Smooth Finished
It provides a soft calendar that is often required for superior print quality and convertibility. This type of paper is commonly used for reel wrapping, carrier bags, fill and seal applications.
2.d) Clay Coated Kraft
A bleached kraft paper can be coated with clay to enhance its opacity, smoothness, and printability. It is often coated with silicone on one side and used as a release liner. This provides dimensional stability and lay-flat benefits, which is why it is commonly used in the graphic art industry.
2.e) Medical-Grade Bleached Kraft Paper
These are typically produced for sterile medical packaging and used in the direct sealing process for pouches, reels, form-fill-seal applications. They also offer barrier properties in several wound and adhesive medical applications.
This type of bleached paper must adhere to the US Food and Drug Administration standards for sterilization.
Since kraft paper has tons of applications, large volumes of these papers can be found in the waste streams of manufacturing companies, warehouses, and distribution centers. For those companies drawing away kraft from the waste stream is an effective way to increase recycling rates.
While specific recycling techniques differ based on the constraints and facilities, most of them involve three fundamental steps:
1. Gathering and Sorting: The very first step is to determine whether the kraft paper can be recycled. Those coated with wax or glazes are very difficult and expensive to recycle. Good kraft papers are separated out and then sorted according to the material that cannot be recycled.
2. Bailing and Shipping: After properly sorting the kraft paper, the next step is to efficiently bale the products to reduce transportation costs.
3. Milling: Once the kraft material reaches the source center to a mill, it is pulped and used as feedstock for new paper products. The milling process involves a series of steps: pulping, screening, ink removal, dispersion, bleaching, water/chemical treatment, and solid waste handling.
The market price of recycled kraft paper greatly relies on its fiber quality and strength. In most cases, the recycled product contains a small portion of contaminants (such as dirt, food waste, oil, and scrap steel), which degrades the fiber quality and brings down prices.
Kraft paper market by region
In 2017, virgin natural kraft paper accounted for the highest market share (over 48%), owing to its numerous applications (due to its great strength and tear-resistant characteristics). Western Europe and North America dominated the global market share, with Europe accounting for approximately 25% and the US for 28%.
From 2020 to 2025, the global kraft paper market is expected to grow at a CAGR of 3%. It will reach more than $18 billion by 2025.
The key factor behind this growth is the increase in demand for kraft paper in several end-use industries, including consumer durables, cosmetics, and food and beverages. Kraft paper’s recyclability feature and rapid urbanization across regions will also significantly contribute to the growth of the kraft paper market during the projected period.