In Papermaking Land

Introduction

Allow me to take you on an imaginary tour for a change. Assume that we could enlarge the world of papermaking with all its components by some 1000ds of magnitudes. This only to help you envision the sizes and dimensions of the involved components in a more daily perspective.

A brief Tour in the World of Papermaking

The Laboratory Manager arrived at her suburban home late in the afternoon after a hectic day with meetings, on-line discussions, challenging resource talks and novel sustainable product concepts. Feeling relieved for being back home after another rough day her son met her inside with a warm hug. In an excited voice he immediately started explaining about today’s chemistry lecture. His class had visited a research lab where they had learnt about wood, fibers and papermaking in general. The 4th-graders had also got a chance to make their own colored hand sheets. Back home having made some research on his own on Wikipedia and YouTube he was overflowing with excitement. He was keen to know more and shot a continuous stream of follow-up questions at his mother: How are the fibers built? What makes fibers white? How can some papers be so smooth and strong, yet so thin? His mother said, let’s first have some dinner and then I can try to tell you and your sister a bit more. Right now, I need a break and some energy, please allow me this my dear son, will you.

Having discussed the world of wood and pulping during the dinner her kids were introduced to the fibers. A row of follow-up questions on papermaking was fired at her. With a degree in process chemistry majoring in fiber and wood analytics she was securely in her comfort zone. She was however, a bit lost for a suitable opening on the educational discussion with her children. She now favored a more playful tone and after dinner her thoughts wandered: “could we shrink ourselves just like in the sci-fi flick “Fantastic Voyage” (1966), the ’80s popcorn “Innerspace” (1987) or the Marvel story “Ant-Man” (2015)? What would our world look like on this scale? – No that’s beyond their history horizon…” Our imaginary skills are limited when it comes to abstract visualization but for kids this just might do the trick. She decided to take them on an imaginary journey in Papermaking Land using imaginary rescaling[1]. –Ok kids, time for homework, unless you did them already.

Later she grabbed her calculator and sat down with her kids and started tentatively:

– Now mummy’s sweethearts, John you wanted to know more on papermaking. This is quite a complex issue, but I’ll try to explain some of the involved issues to you. –Are you interested to join, Jessica? Her daughter replied smiling: –For sure mum! Ok then, let’s all try being sort of Antmans while imagining a 3D-magnifying glass zoomin’ the fibers, fillers and paper machine by, say, 100 000 times. Here things become more graspable in size for us: a papermaking fiber (conifer wood) would compare to a freight train of 200–350 m with a diameter of 5 m. The shorter fibers (deciduous wood) would equal public trains of 70–120 m with diameters of 4–5 meters. Since fibers are hollow and cylindrical in shape; like long, slender worms their walls would measure 0.5–1 m. The so-called fine material would here slip through holes of size 7×7 m (200 mesh). These are released from fibers and present in all papermaking stocks and would vary from vacuum-cleaner hoses to large bulldozers in sizes. These come in all sorts of shapes: from thin and slender worms (fibrils) to large blocks. –Are you following me? –Do you get some of the picture my son? –Yes mum, what size would a red blood cell or one of Jessica’s hair then be? She grabbed her calculator. –Hmm, let’s see: a red blood cell is 8 µm and single hair is about 50-100 µm in diameter and may even be up to 1 m long. –Enlarged these would then correspond to a bathing ring of 80 cm without middle hole, instead somewhat thinner at the center. A single hair could compare to a 5–10 m thick rope, here Jessica’s waist-long hair would be 100 km long… The kids wowed and laughed and started to horse around imagining a gigantic pair of scissors arriving. –What about dust mites and head lice then? She calculated again: –The dust mite would here be about 25 m long and a head lice some 250 m… –Wow, awesome: they would totally destroy a T-Rex!

Having settled down, they continued: –Now, looking at a paper machine in this scale makes you maybe understand the size proportions in the Land of Papermaking. If we would zoom up a 10-m wide wire-section 100 000x this would correspond to 1000 km–the distance between Helsinki-Ylläs (in Lapland) or London-Berlin–with a length of 2-3000 km–equaling the distance Helsinki–Madrid. A full-length paper-machine ca. 120 m long would therefore match the diameter of earth… –What? Really? That’s just incredible, replied Jessica in a thoughtful voice. –How’s that possible? –We use an enormous machine to make paper of such tiny fibers. –Yes, that’s true but it’s all about knowing the fibers and the way they behave in the different stages, wet and dry. Cellulose itself is amongst the strongest materials in nature, you know. We have learned to utilize these natural structures in a quite efficient way.

Her mum took up the story again: –On the paper machine the diluted fiber suspension, slurry or stock as we call it, is fed along and onto a perforated rotating wire as you remember: this mesh is like a tea strainer, only very large and flat only a bit smaller holes. Think you can picture a wire? It is like a wide and planar, moving belt rotating between two thick rods. She sketched on their mini black board. –The rectangular perforations would size ca. 20×20-m (ca. 70 mesh), bottomless swimming pools, for sieving out the water and keeping the fibers on the wire. -John, you saw the principle when you made your hand sheets. He immediately ran off to get them, when back they all examined them a bit closer together.


Table 1. Comparative size-estimates of various papermaking components in Land of Papermaking.

Item Actual size x 100 000 Relative size Number/L
Paper machine 120 m 12 000 km ca. Earth diameter
Wire 10 x 30 m 1000 x 3000 km Helsinki–Madrid
A4 297 x 210 mm 30 x 21 km Surrey Hills–Big Ben Xx Big Ben–Heathrow
Fiber, length 1–3 mm 100–300 m Public–freight trains 2–4E6
Wire thread 250 µm 25 m Length of a heavy combination vehicle (8-10 axles)
Wire holes (70 mesh) 210 µm 21 m Swimming pool
Paper thickness 70–180 µm 7–18 m Height of a 2–5 store building
Fiber, width 20-45 µm 2–4.5 m Small– large car dimensions
Fines 1–75 µm 0.1–7.5 m Smart phones–trucks 10–50E6
Polymer (HMW) 30 µm 3 m Fishing line 2-4E14
Starch polymer chain 5-15 µm 0.5–1.5 m Length of a child
Fiber, cell wall 2-5 µm 30–50 cm House walls
Filler (e.g. talc) 2 µm 20 cm Food plate 9E11
Bentonite 300 nm 30 mm Gravel stone or metal coin 4E13
TiO2 (rutile) 150 nm 15 mm Cube of white sugar 5E13
Nano particle (SiO2) 5 nm 500 µm Table sugar grain 6E16
Cellulose elementary fibril ca. 2.6 nm 260 µm Toothbrush bristle
Synthetic polymer chain diameter 1 nm 100 µm Thin hair
Glucose molecule unit 7 Å 70 µm Length of a sperm cell
Water molecule (Van der Waal radius) 2.82 Å 28.2 µm A 360 sandpaper grain 3.33E25
Hydrogen bond 2.5 Å 25 µm A 400 sandpaper grain

 


Table 2. Unrelated, trivial objects for size comparative purposes in Papermaking Land tale.

Trivia Actual size x 100 000 Relative size
Human hair, length 1 m 100 km Bremen–Hannover
Human hair, width 75 µm 7.5 m Big Ben clock diameter (dials)
Coffee bean 8 mm 800 m 2xUluru
Hair lice egg 1 mm 100 m Football field (length)
Salt grain 0.5 mm 50 m Colosseum outer wall (height)
Bacteria 250 µm 25 m Heavy vehicle combination
Tobacco smoke particle (min) 10 µm 1 m Your front door width
Spider silk (diameter) 4 µm 40 cm Chair width
Chromosome diameter 1 µm 10 cm Two chicken eggs
Flu virus 130 nm 13 µm Household dust particle
DNA helix width 20 Å 0.2 mm 70 mesh papermaking wire opening

 


–You know, if we looked at an area the size of an A4 on the paper machine wire we could tell that this in size would compare to Big Ben–Surrey Hills in height and Big Ben–Heathrow in width. This wire area would be filled with holes the size of swimming pools ca. 25 m apart, all in all some 350 000 holes per A4 corresponding to an area of 620 km2. The fibers size of freight trains is collected onto the perforated web while water is being drained off. We call it dewatering. –Mum, you mean in principle I do the same when rinsing spaghetti in our colander? –Yes, exactly Jessica! –As the papermaking fibers are relatively expensive we must use cheaper components and additives in the paper recipe. It’s a bit like baking bread or cookies. Except that here we use non-edible mineral filler materials like kaolin, talc or calcium carbonates. Under our magnifying glass typical filler particles would compare to our dinner plates in size. –Yuk, sounds a terrible and hard-to-digest recipe! replied John. –Yes, let’s avoid eating paper. You know, these particles would greatly outnumber those found from any restaurant kitchen coming in amounts of billions per liter slurry. On top of these we need smaller ingredients to make the paper stronger by bonding fibers better together. Firstly, the fibers need some treatment, we refer to this as beating or refining. This will make the fibers kind of furry and flat. You easily realize that two flattened rods have a larger contact area when crossed than two round rods. The beating also makes the fiber surfaces sort of furry. Secondly, we use natural or synthetic polymers as links between the fibers. It’s like tying thin ropes, wires or spider webs between the train-sized fibers and other material. –I can imagine the numerous Spidermen in action there, Mum! –Yes, indeed John, that didn’t cross my mind. If we think of the synthetic, linear polymers applied in papermaking their size would compare to fishing lines in diameter with lengths of about 3 m. The natural biopolymer, starch made from cereals could compare to a slightly branched 5–10 m fishing line. These polymers are important for keeping the fibers together making the dry paper stronger. Imagine as if you were diving in the weirdest sea environment you ever could imagine: you struggle amongst conglomerating, huge train sets swishing by whilst midst in hordes of bicycles, cars and large trucks sized fiber parts jumbling around. The furry and partly flattened train sets would be surrounded and covered by messed-up thin fishing lines attached while caught in the trampled fibers’ hairy-like outer essence. Moreover, everything is whirling around together with a large number of various block, platters, coin-sized and sugar-cube blocks swimming around with a multitude of table sugar grains… On top of all this, the whole system is moving at high speed while the water is being filtered off (read furiously flowing) via the vast number of side-by-side swimming-pool sized holes. (Translated into papermaking vocabulary such a picture equals a LWC PM running at 1200 m/min while dewatering the papermaking stock containing flocculating fibers with fines, cationic starch, a HMW strength polymers, some filler (GCC/PCC, kaolin, talc) applying a nanoparticle system.)

Figure 1. A size comparison of various real and imaginary objects (Lexinator 117).

–On basis of these measures you may now have got a rough picture of the sizes and figures in Papermaking Land. –Yes, indeed mum, that was a fascinating journey replied John in a drowsy tone. –Mum, that was kind of a strange voyage on the paper machine. I bet we’ll dream about odd things…, said Jessica. –Could we have a goodnight kiss. –Of course, my dear ones. Let’s brush our teeth now.

 

Text: Tom Lundin

 

[1] The idea arises from a presentation by a former colleague Mr. Jonni Ahlgren, whose idea I have developed a bit further here.


References

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