new facts about water what to keep in mind if you process plastics brabender messtechnik ® gmbh & co. kg
2 plastics processing is a highly demanding business. this becomes especially apparent if things don't work out as they should: for in- stance, if the plastic in the product has prop- erties which differ from those it should have according to the material data sheet or if the material flows differently to what we have be- come used to or if the injection pressure sud- denly deviates from the target or if the surface quality of the component comes out at a lower quality than we desire. that's where you need your experience! in a high number of cases, experience says: it's the water! in fact, quality and process prob- lems in plastics processing can very often be traced back to one key problem: too high re- maining granulate humidity. liquid water can act as a "softener" which under pressure can impact on the polymer's flow properties. it evaporates at the temperatures used during plastics processing and as such can prevent frictionless filling of tools. it can trigger the breakdown of hydrolysis-sensitive plastics, such as polyamides and polyesters, and can impact their mechanical properties. these are only a few of the ways in which water can be- come a problem in the mouldshop. unfortunately, water can be difficult to fight: humidity only becomes a problem once it forms a droplet around the granulate. the one challenge that injection moulding and extru- sion practitioners face again and again wa- ter isn't visible. in the absence of experiential analyses, it becomes impossible to know how much water the air or granulate might contain, let alone with the kind of precision which cus- tomers require nowadays - and as we know, these requirements are permanently on the rise. even smaller quantities can have a major ef- fect. polar polymers can withdraw problem- atic water content from their surrounding air in minutes - in extreme cases, several percent of their own dry weight! at times, even unprotect- ed transport from the dryer to the equipment can be sufficient to contaminate the plastic with water. the result: an extensive search for errors, greater maintenance costs and expen- sive returns. these are problems that anyone in an industry under increasing competitive pressure can ill afford. but there is a way to deal with such challeng- es, experience plus a high-performance, highly precise, reproducible remaining humidity anal- ysis system. brabender messtechnik gmbh brabender messtechnik® gmbh & co. kg kulturstraße 51-55 d- 47055 duisburg tel.: +49 203 99819-0 www.brabender-mt.de firstname.lastname@example.org contact us experience is in demand! tel.: +4920399819-0
3 and co kg offers you a combination of both: brabender has been supporting its customers in the plastics industry for decades with its re- liable aquatrac. the aquatrac station is the next step in brabender's aquatrac development: the revolutionary remaining humidity analysis device, which finally works completely without auxiliary chemicals and laboratory gases, provides outstanding preci- sion and thanks to its smart menu system, can be used by just about anyone. in the plastics industry, water is everything but a "precious resource" - on the contrary! however, the highly specialised analysis de- vices in the aquatrac range enable you to effectively remove any problems, which water vapour and remaining humidity might cause in the granulate, in advance. why water becomes a problem in the first place: find out in this introductory brochure. below we will go into detail about the special challenges involved in e.g. injection moulding and extrusion. we hope you enjoy the read – and make many useful discoveries! your brabender messtechnik team introduction
4 water? of course: it comes from the tap, quenches your thirst. it's the main ingredient of coffee, beer, wine, juice, and even us people: around two thirds of our weight comes from the water in our cells. which is why there is no life without water! everybody knows water - and has stories to tell about it. involving beach holidays, a diving course, a neighbour's pipe breakage and the last time the rhine broke its banks. what could be new about that? we say: quite a lot! many people, includ- ing professionals, might be very surprised to find out where we can find water outside the bath tub, swimming pool and so on. this sub- stance, which chemists describe as a simple combination of one part oxygen and two parts hydrogen, is basically everywhere. the earth contains vast quantities of it. there are good reasons why our home in space is known as the "blue planet" - two thirds of its surface are covered in h2 o – taken together, this makes up an incredible 1,300,000,000 cu- bic kilometres. but the presence of this "precious resource" isn't always beneficial. for instance, in the plastics industry, water can be responsible for a whole range of problems. wet plastics become a challenge again and again - even where the factory-fresh granulate feels dry. how do we discover this in the workshop, with- out the need for an expensive lab and great effort, and how do we tackle the root of the problem? the following pages will tell you! water is everywhere. not only in your bathroom and kitchen, in rivers and seas, but also in plastics which look dry at first glance. and yet it shouldn't be there and can even cause problems. chapter 1: what is water actually?
5 water is life – and fun! as long as it does not make our lives difﬁcult by occurring in plastic granulate. 5 new facts about a substance that everyone knows
6 the last chapter did not mention one important site where we can find water in nearly inex- haustible quantities practically everywhere on earth: the atmosphere. in many parts of the world, one look out of the window will show you: clouds are nothing more than flying wa- ter tanks in which the elusive substance trav- els across continents and oceans as minute droplets or ice crystals. it isn't surprising then that poets sometimes call this world above our heads a "sea in the skies". in fact, depending on the exact atmospheric conditions, temperature and height, water can be the third most frequent component of our atmosphere after nitrogen and oxygen: when- ever researchers take samples of the air that we breathe, these frequently reveal between a bone-dry 0.0003 and a heavy four percent of water. as such, h2 o occurs more frequently in the atmosphere than even the greenhouse gas carbondioxide: for decades now, researchers interested in the chemical side of our atmos- phere have kept a close eye on water as an influencing factor - and have been incorporat- ing it in their climate analyses. clouds are only the visible part of the water circling around above our heads and in the air that we breathe. overall, the atmosphere transports close to 13,000 cubic kilometres of h2 o around the planet! that's about the same as is located in the wet soil beneath our feet - incidentally, approximately half this much wa- ter evaporates from the rivers and lakes each year. thankfully, this does not stay in the sky indefinitely: it returns to earth through precipi- tation. in a so-called humid climate, such as between the fifth degree south and the 12th degree north, close to 2,000 litres of rain can fall on each square metre per year. however, it isn't really as simple as all that. you may have asked yourself why in the hot- test summer months, wet washing on your bal- cony sometimes just doesn't seem to get dry, whereas in the dead of winter, you can some- times take it down from the line in only a few hours. how is this possible? we know that air can absorb significantly more humidity on a hot day than on a cold day: at ten degrees, this can be around nine grams of water per cubic metres, and on a hot summer's day, this can be around 30 grams (incidentally: the air can still absorb water vapour in minus temperatures). but the problem is, you can't see how wet the air is already! and on hot days, water will be evaporating from other sources. also, if you have a garden pond, you might know that in the summer heat, the water surface can eas- ily lose around five litres of water per square litre in a day. if a shower around your washing line has created a few puddles, then the air will be full of evaporating water for a while. and in the air can be full of water vapour and you would not be able to see it. this should ring alarm bells for plastics processers: only a few milligrams of water in the granulate can make the difference between "well done" and expensive returns. and they can easily come from the air. chapter 2: invisible and still there nonetheless
7 spite of the high temperature, there is no more capacity for the water in your wet clothes. anyone processing plastics should keep this in mind since plastics can of course not be pro- cessed in a hermetically sealed room. luck- ily, nowadays, complex computational models such as those used by climate researchers are no longer needed to determine the influence of the water in the air on the remaining humidity of the plastic granulate. there is a much easier way: ultra-precise measuring equipment such as aquatrac station can be used to deliver reliable figures without the need for laboratory white-coats. and even without the need for chemicals. all you require is an empty space next to the dryer or extruder. if your washing won't dry even though it's hot, that's because of high air humidity. be careful: even dry plastics can get wet! 7 water in the atmosphere
8 talking about climate research, clouds may look fluffy, but they are making it very hard for researchers to analyse them mathemati- cally. the formulae used by atmosphere chemists to e.g. calculate evaporation rates or saturation concentrations - the points when water vapour becomes water drop- lets - might remind you of particle physics. thankfully, we can leave those to the scien- tists. all that a plastics processer needs to know in order to deal competently with the humidity problem can fit on only a few pages: these ones here. in principle, you should be aware of only a few terms – smart analysis devices such as the aquatracstationbybrabendermesstechnik gmbh & co. kg will do the rest for practitioners. insert the sample, start the analysis, adjust your drier based on the measurement results – and check again every now and then that everything is working right, such as on the way from the dryer to the extruder: those are the key aspects. the aquatrac station is inten- tionally designed such that it can be operated entirely without laboratory white-coats, com- puters and a degree in chemistry. one term which summarises much of what we have said is that of air humidity, otherwise known as air moisture content. this means: the proportion of water vapour in the atmos- pheric gas mixture surrounding us - such as the production workshop. water vapour means the gaseous, invisible form of water, and not the steam rising in droplets that we are famil- iar with from cooking. this explicitly does not mean visible water in the shape of ice crystals or water droplets - which physicians call con- densed phases. we must also distinguish between absolute and relative humidity. absolute humidity states the amount of water specifically contained in the air - i.e. a figure which could also be rough- ly estimated using scales. 100 grams of water evaporated in one cubic metre of desert air would thus result in an absolute air humidity of 100 g/m3 . always assuming that the air was really dust-dry beforehand - which is not nec- essarily the case even in the hotter regions of the world. the trade winds in the sahara can easily have a remaining air humidity of 20%. which brings us to relative humidity, which is also stated in percent as in this example of the sahara. it defines a relationship be- tween the actual air water content with the maximum water that the air could absorb un- der the given circumstances. this quantity in turn depends on the so-called saturation vapour pressure of water – and this rises exponentially with the temperature. the rea- sons for this are complicated interdependent one cubic metre of air can contain up to ten grams of water. and that's not even all: extrapolated to a typical workshop, this can quickly turn into several dozen litres - they should definitely be included in your plans! chapter 3: humidity analysis without white coats and chemistry
9 processes on the surface of the liquid. but the most important thing is this, hot air absorbs a lot of water, cold air will contain a lot less. let us distill one figure as a quintessence of all the curves and formulae that we have cho- sen not to include here. as a practitioner, you should remember: one cubic metre of warm air with a temperature of 20 °c can contain around 17 g of water at normal pressure levels. that's the maximum air humidity. the optimal relative humidity in living areas(!) is stated as being 40 to 60 % – this corresponds to around 8.5 g/m3 of water in absolute humidity. a workshop which is five metres in height with a basic area of 500 square metres might there- fore easily contain more than two ten-litre- buckets' worth of water, which nobody can see and which, in the worst case scenario, nobody has planned for. and at higher temperatures, there can be even more. : a watering can can hold around ten litres of water. the air in a typical workshop might contain several times that. be aware of that! a watering can can hold around ten litres of water. the air in a typical workshop might contain several times that. be aware of that! 9 expert knowledge i: relative and absolute humidity
10 the chapters above have shown us this: the amount of water that the air in a room can contain depends on many factors which even the most skilled engineer can't possibly keep in mind at all times - even if he calls up the weather forecast on his screen every hour. and: air can contain a lot of water even if we cannot see it. one simple example from nature can show us just how much "a lot" can be: mist. a typical autumn day, the sun is shining, but at dusk it gets quite cool. and suddenly the mist rises. what's happening? where is it coming from? there's a simple answer: warm air has ab- sorbed a lot of water during the day, and this now cools down - the invisible water vapour condenses into fine droplets because at lower temperatures, water prefers to be liquid rather than gaseous. water which we could not see before suddenly appears: and we can of course use this effect to measure humidity! even for an especially precise variant: determining the dew point. that's what we call the precise temperature at which water vapour becomes mist and fine droplets are deposited on cool surfaces. in other words: the temperature at which the air is saturated with water. expressed even dif- ferently: the temperature at which the relative humidity in the air is precisely 100%. which is why the dew point temperature is very closely linked to the air water content. a rule of thumb without formulae: if the air con- tains a lot of water vapour, the dew point is higher; if it contains less, it is lower. to use an image: the more water floating in the air, the more likely it is that it will become liquid when the air cools. by contrast, low water vapour needs to be "forced" out of its gaseous state with low temperatures. the link between the dew point and water content can be deduced from the so-called dew point curve for water. let us stay with our example of mist: all that we need to measure the dew point is a small metal plate which we can cool down slowly. thought experiment: it's daytime, the tem- perature is a sunny 25 °c, we hold this small plate up in the air and cool it down slowly. at 16 °c, it suddenly starts to become cloudy – that's the dew point. one look at the dew point curve shows us: at this temperature, water vapour can only condense if the air contain precisely 13.2 grams of water per cub metre of air. incidentally, at an ambient temperature of 25 °c, this means a relative humidity of 57 %. in fact, a lot of similar methods are used to measure the dew point. clever modern sys- tems no longer need to wait until the sensors actually become cloudy - instead, they are able to determine the dew point based on the mist is nice thing: it finally reveals to us how much wa- ter is hovering in the air. meaning above the temper- ature at which fine droplets form, i.e. condensed out. in fact, we can precisely measure the water content based on so-called dew point temperature measure- ments.that'sthetechnologybehindtheprecise,new aquatrac station. chapter 4: what you can learn from mist
11 water vapour cover at other temperatures. the capacitive sensor registers precisely how many water molecules are deposited on its surface - and based on this can determine when it would be completely covered under the given circumstances. this begs the question: why don't we just measure relative humidity and deduce the absolute water content in the air from this? there's a simple answer: because measuring the dew point is much, much more precise. the dew point depends on the absolute water con- tent in the air and the gas temperature, among others. and all the data and tables needed to convert the dew point temperature into abso- lute air humidity values are set physical data which have been known for a long time and which have been determined to ever greater precision over decades. therefore they are ideal for extremely precise measurements. next question: why do we need to know this? this might not seem relevant for injection moulding, extrusion and similar technologies. but dew point measurements are what's be- hind the aquatrac station by brabender messtechnik. now you know why the device is so precise. if you have ever walked through mist, you know how much water the air can contain: mist makes it visible. and we can use this effect for ultra-precise humidity measurements. if you have ever walked through mist, you know how much water the air can contain: mist makes it visible. and we can use this effect for ultra-precise humidity measurements. 11 expert knowledge ii: dew point
12 nevertheless: the question at the end of the last chapter is of course justified, be- cause the links between the dew point, rela- tive and absolute humidity and the saturation vapour pressure and so on are complex. but why should you have to deal with that at all? what do practitioners care whether there are two or three watering cans' worth of wa- ter in their workshop air so long as they stay gaseous? air which is too dry is also un- healthy. and why are there dryers, after all? as so often in life: it isn't really as simple as all that. water can disrupt plastics processing in so many different ways that we should do all we can to safely exclude it from the produc- tion process and particularly from the granu- late. a remaining humidity which is too high not only impacts on the mechanical properties of many plastics, it also influences their flow action, injection moulds and surface quality. it can also trigger the hydrolytic decomposi- tion of susceptible materials, such as polyes- ter or polyamides, prevent correct tool airing and contribute towards the formation of cast coating. in short: undesired water can make production processes unpredictable, increase maintenance costs and result in returns. unfortunately, humidity doesn't only become a problem once morning due visibly settles on the granulate: this so-called surface humidity, which it is easy to dry off quickly, is the least of your problems. if you expose your granulate to moist air for a longer period, you risk wa- ter running to the inside of its core ("diffusion") until this part also reaches an equilibrium with the moisture content of the outside air. this is called the core humidity, which is much more difficult to handle. for this, you have to know exactly what settings to use on your dryer. you might only be drying off any water attached to the surfaces, while enough water remains in the fine capillaries and pores of the granulate to disrupt the processes and impact on the material properties. it's a better idea to check regularly and to determine absolute water val- ues. a workshop isn't the place for a humidity measurement based on your "gut feeling". and as if that isn't enough, some plastics have such water-affinity that they practically suck humidity out of the air: they are called hygro- scopic plastics, i.e. pa, pbt, pet, pc, abs and pus. chemically speaking, this is because these polymers are "polar polymers" - they contain groups of molecules which take nega- tive charged electrons from other molecules which creates partial charges in the polymer chain. in the same way as water, where oxy- gen attracts the electrons in hydrogen. and since opposite charges attract, hygroscopic, water vapour can be a real problem especially for hygroscopic plastics: they simply pull the water from the air. and if you don't want to fail your customers' quality checks, make sure to check the water con- tent of your materials! as often and as precisely as possible. never use just a rule of thumb! chapter 5: facts instead of a gut feeling
13 polar plastics such as polyamides basically pull water from the air. at 23 °c and 50 % relative humidity, pa 6 can quickly add up to over three percent of its own weight in water from its environment – even on the short tip from the dryer to the extruder. note: one kilogram of dried plastic contains only around 80 milligrams of h2 o – 0.0080 % or 80 ppm. fillers such as glass fibres can also be highly ready to attract water. only unfilled, absolutely non-polaric materials, such as poly- olefins whose molecule chains have no notice- able partial charges, are in the clear. dry or not dry? even if you can see no water droplets, the granulate core might still be moist and cause trouble during processing. if you want to be sure, regularly check remaining humidity. 13 expert knowledge iii: surface water and core humidity, hygroscopic and non-hygroscopic polymers
14 the chapters above have given you a limited first glance at the problems which can occur if plastics processers ignore aspects such as air humidity and remaining humidity. to sum- marise: you should always know how much re- maining humidity is contained in the granulate used in order to establish a reproduceable, reli- able processing process and to prevent returns. this can quickly mean that you find yourself in the dark. if you openly store plastics with an affinity to humidity, the valuable granulate can soon consist of ten percent water – even though the data sheet for the components re- ceived at your workshop only states 0.1 %. and that's only one way of many in which wa- ter can "contaminate" your raw materials in your everyday work. that's not only a problem where the process- ing process is calibrated to different remain- ing humidities. there is one important aspect which we have not mentioned yet: cost-effec- tiveness! who would want to pay the price per kg for special polymers if they are really just: water? the following applies, here, too: trust is good, control is better. as a result, humidity analyses and incoming goods checks should go hand in hand. and one further aspect is also often over- looked: drying costs. experienced processer will put their granulate through extensive dry- ing cycles before they entrust it to the process- ers to make the end product. but even apart from the fact that some plastics are able to pull so much water from the air even betwen the dryer and the extruder that quality control must spend additional shifts searching for errors:. what if the drying time isn't even enough to prepare your polymer optimally? it's a better idea to measure regularly whether the process does what it promises in the first place. and whether you are financially still making good: for instance, a dew point of between minus 20 °c and minus 40 °c rep- resents such a low water content that further drying would be possible but hardly financially viable. and not ideal in terms of process tech- nology, either. to look at it another way: if you end up using longer drying times than needed because your plastic has already reached optimal remain- ing humidity for your equipment, you are liter- ally burning money - which you could save by checking regularly how much water was actu- ally removed from the plastic. a number of analysis processes are available on the market which enable you to measure more or less precisely how much remaining plastics processing and water: quickly prevent any hidden problems through precise remaining humid- ity analyses. thanks to its smart dew point meas- uring process, the new aquatrac station by brabender messtechnik works without laboratory gases and auxiliary chemicals – and yet provides reproduceable, highly precise results. including in the workshop - say goodbye to the white coats! chapter 6: what now?
15 humidity your polymer from the octabin in your goods' yard still contains. but these have significant disadvantages: some only work in a lab or only really make sense to chemists, others are workshop-compatible but not very precise because they don't only "measure" the water content but also all other liquid compo- nents of a plastics charge. they might there- fore overestimate the required length of the expensive drying cycle. this is where brabender messtechnik gmbh & co. kg can help. brabender has made humidity analyses workshop-compatible at the highest level, even in the previous – mobile – models of theaquatrac range. with the aquatrac station, brabender messtech- nik is now taking things one step further: this highly precise tool records the exact remaining humidity contained in the polymer without be- coming distracted by volatile additives etc. and thanks to the new dew point measuring princi- ple, this is possible without laboratory gases or other auxiliary chemicals. easy-to-use, smart display control included. simply insert the polymer, close the sample container and wait - that's how simple a pre- cise remaining humidity analysis can be. eas- ily save costs and avoid returns. finally! remaining humidity analysis entirely without laboratory gases and auxiliary chemicals, and immediately next to the equipment: insert the sample and read the exact water content only a while later: it's possible now! 15 a smart solution to humidity problems
new facts about water v1 / en / 10-2016 brabender messtechnik® gmbh & co. kg kulturstraße 51-55 d- 47055 duisburg tel.: +49 203 99819-0 fax: +49 203 99819-22 www.brabender-mt.de email@example.com tel.: +4920399819-0 fax: +4920399819-22