Talc s Multiple Functionality In The Paper Recycling Process Peter Biza Imerys Pigments for Paper & Packaging

Size: px

Start display at page:

Download "Talc s Multiple Functionality In The Paper Recycling Process Peter Biza Imerys Pigments for Paper & Packaging"

Jasper Webb
6 years ago
Views:

1 Talc s Multiple Functionality In The Paper Recycling Process Peter Biza Imerys Pigments for Paper & Packaging ABSTRACT Talc, because of its strong organophilic nature has, over decades, been employed, successfully in paper mills in order to pacify both micro and macro stickies. More recently, additional features that give talc a unique, distinctive advantage improved removal of stickies at the flotation and hydrocyclone cleaner stages as well as removal of detrimental organic impurities from the PM water circuit - have emerged. Collectively the separation processes in conjunction with pacification means that overall talc is an extremely efficient treatment for stickies and other hydrophobic substances capable to disturb paper making. In this presentation the well known pacification process is briefly reviewed and the additional benefits of talc in the pulp and paper production are considered. In the pacification step individual stickies particles are enveloped either partially or completely by talc. The thin layer of talc renders the pitch or sticky particle less tacky and significantly less prone to form deposits. Consequently the now innocuous contaminant leaves the paper machine with the finished paper. It has been empirically demonstrated that the inclusion of talc before flotation significantly improves the rate of stickies removal during this processing step. In the separation process in cleaners the sticky particle is again enveloped in talc. The thin layer of talc then serves to increase its size and importantly its density to a critical level where it is more readily removed by centrifugal force. In the paper machines water circuit finally the organophilic talc surface can actively help to remove detrimental, hydrophobic material that otherwise would disturb the sheet formation and strength properties. An idealised system includes addition points upstream of flotation and hydrocyclone cleaners for improved removal as well as post cleaners for pacifying remaining stickies and helping to clean up the water circuit.

Talc, A Natural Platey And Hydrophobic Mineral Talc is a hydrous magnesium silicate, with a theoretical chemical composition of Mg 3 Si 4 O 10 (OH) 2, also described as 3MgO 4SiO 4 H 2 O.

2 Talc, A Natural Platey And Hydrophobic Mineral Talc is a hydrous magnesium silicate, with a theoretical chemical composition of Mg 3 Si 4 O 10 (OH) 2, also described as 3MgO 4SiO 4 H 2 O. Other names for talc found in literature are steatite, normally used for high purity talcs or soapstone, often used for talc rocks used for carving. The mineral talc belongs to the group of phyllosilicate with a layered structure based on infinite sheets of silicium-oxide tetrahedras on top and bottom of a three layered cristal. The middle layer consist of a brucite like octahedral MgO4/OH2 layer (Figure 1). The units of Si- Mg-Si layers are hold together by weak Van der Waals forces. This structure with very unpolar, flat and hydrophobic on both surfaces of the platelet gives talc some very special properties that are not found within other minerals. Due to the absence of ionic or polar groups on the surface the individual talc layers are easy to separate giving rise to talc s very soft nature and it s slippery feeling. In Mohs hardness scale talc is ranked 1, the softest mineral on earth. This softness is appreciated in numerous applications of talc in daily life. The soft, even greasy feeling of cosmetic powders in many cases is due to the presence of talc as a main ingredient of the formulation. It s softness make talc also used as a lubricant in numerous applications. The silicium tetrahedras with only little possibility for chemical attack gives the mineral a high level of stability when used in paper making, pharmaceutical formulations or as food additive. What makes talc unique amongst minerals is its very hydrophobic behaviour along the planar surfaces. The surface energy of talc is almost as low as that of most synthetic polymers such as polyester or polyamide. This surface property makes talc also organophilic, resulting in the ability of talc to adsorb organic substances. This makes talc e.g. easy to disperse into polymers during extrusion or makes it an excellent pigment of choice for water and moisture barriers. Talc s adsorbent properties for organic substances are also used for water treatment. The three main properties that makes talc interesting for the use in paper production are - its plateyness, important mainly for the coating application including barrier coatings, - its softness, advantageous when used as a filler but also in coating - and its organophilic behaviour, the main property used during paper recycling to control different kind of organic substances.

It took only few years before this application spread to other regions of the world.

3 Talc Use In The Paper Recycling Process The first well known use of talc in pulp processing is the control of detrimental pitch and stickies. The real industrial use of talc for pitch control started in the early sixties of the last century in the United States. It took only few years before this application spread to other regions of the world. With the increased importance of paper recycling talc started also to be used for sticky pacification in recycled pulp. The list of contaminants in waste paper is long. Some have their origin already during paper production. So could resin coming from the trees or latex binder used in coatings be counted as problematic impurities when it comes to paper recycling. More impurities are added during paper processing like inks during printing, glues used in book binding or with numerous synthetic chemical additives requiring dispersants, emulsifiers, surfactants, etc. The last source of real contaminants in waste paper is the end consumer. Many of the problematic materials are of organic composition. They often have a hydrophobic surface and some of them are tacky under paper making conditions. They are consequently the principal cause for the build-up of stickies in the recycling process. Glues, hotmelts and other adhesives always have a very low surface energy to make them better spread on all possible surfaces. The reason why talc is perfectly made to control these stickies is its organophilic, low surface energy of the planar oriented silicium oxide tetraeders. This surface enables talc to adsorb onto sticky organic material and cover the tacky surface to prevent agglomeration and deposits caused by such material. The mechanism is simply based on the gain of energy. When talc adsorbs onto the surface of hydrophobic stickies, water molecules are removed from the organic surface and substituted by talc s organophilic silicate surface. This brings both the talc and the stickies into a lower, more comfortable state and liberates adsorption energy. One of the best known effects of talc is the pacification of organophilic material to reduce their tackiness and avoid depositions on felts and fabrics but also anywhere else in the system. When adding talc before places with increased formation of deposits it will based on above mentioned mechanism help to significantly reduce the deposition tendency of tacky material. The reduction rate of deposits will depend on the nature of the organic material, the talc dosage rate, ph value of the water and several other system parameters. When simulated in the laboratory with a plastic beaker test deposit reductions of more than 90% can be achieved as shown in the graph on the right. Water Circuit Closing, A Good Reason To Use Talc The paper industry has continuously improved its environmental record by reducing pollution of rivers and water consumption by closing water circuits in production sites. Fresh water consumption was drastically reduced in the last decades and continues to as more and more water circuits are closed. This development requires an adaptation of technology as well as of the chemicals used. While in open circuits a chemical dispersion of detrimental substances in the water before a washing step helps to remove them from the system, the same chemical will cause enrichment in a closed loop which after a while will lead to an overloaded system followed by increasing problems. One can avoid this enrichment, if you have a method to take these organic substances out of the process instead of dispersing it in water. Talc is giving you minimum two options for this in the recycling process. One option is to use talc to increase the specific weight of stickies so that consequently they can be removed by heavy weight cleaners. These cleaners will remove particles based on their density, shape and size. Modern cleaners start to be efficient if the density difference between the fibre suspension is minimum 5%. As the specific weight of talc is around 2.8 g/cm3 only a small layer of talc platelets on the outside of a tacky particle will be enough to bring up its density into a range where it can efficiently be removed from the system in centrifugal cleaners. The graph on the right shows that in a mill trial sticky removal

$Typically flotation in a deinking line is optimised to remove ink particles of a certain size fraction.$

4 could be increased to more than 50% in cleaners reflected also in a significant growth of sticky load in the rejects. Another positive effect of talc can be observed in the flotation process. Typically flotation in a deinking line is optimised to remove ink particles of a certain size fraction. Stickies, always hydrophobic, will also partly be removed in this process step if they have the right size and density. Recently it was published, that talc also helps to more effectively remove stickies during the flotation process. Obviously the presence of talc supports the formation of sticky-talc complexes of the right size, density and hydrophobicity that they can then be removed from the system together with the ink particles. This effect is demonstrated in the graph on the right. Together with the effect in cleaners talc helps again here to not only pacify detrimental tacky particles but also remove them completely from the system. Cationic Talc To Reduce Anionic Trash In The System Since the introduction of neutral papermaking the anionic charge in a paper making system has significantly increased. The higher ph leads to increased negative surface charge that papermakers try to control with higher levels of cationic fixing agents and retention aid polymers. The negative consequence of the excessive use of cationic polymers is that the zeta potential of fibres is brought closer to zero and instead of getting better sheet formation the risk of flocculation effects is increased. To counter this development a cationic talc quality was developed that is capable to reduce the amount of anionic trash in water circuits but does not cause any unwanted change of fibre s zeta potential as the cationic charge is fixed on the talc surface and adsorbs anionic particles onto the talc surface consequently reducing the necessary amount of cationic polymers, their negative effects and costs. Cationic talc has proven in numerous mill applications that it successfully reduces anionic charges in the system without any negative influence on zeta potential of fibres. In some systems cationic talc also showed better retention in the paper sheet than standard talc. Talc Gives Great Opportunity To Improve Numerous Chemical Interactions Today so many different chemicals are added in a paper mill, that really nobody can estimate all the reactions and interactions that happen. Talc will not give any detrimental chemical interactions in the mill with process chemicals. That also means that no dangerous, toxic or harmful products can be formed by chemical interactions with talc. Nobody can exclude this possibility with the numerous chemicals that have some reactive groups left in the molecule. But today it is one of the requirements for a modern additive to exclude any possibility of formation of dangerous derivatives. Dispersants for sticky reduction in deinked pulp can have a negative side effect of dispersing printing ink particles. This will reduce the flotation efficiency which has a negative influence on the brightness and cleanliness of the pulp. Talc causes no dispersing of printing inks in the water and if talc adsorbs printing ink particles, it will not cause problems as talc is quite well removed in flotation process too. Talcs Positive Effect On The Paper Machine Last but not least talc shows very positive effects on the paper properties itself, especially when used in the right, carefully selected addition points near the paper machine. To determine the right addition point an in depth system analysis of the disturbing substances in the system is necessary. Hereby a recently developed analysis concept provides the necessary information to dose the correct talc level at the right point of the paper machine circuit. Using again its organophilic surface the talc particles will efficiently collect the disturbing substances and prevent them from disturbing the fibre-fibre bonding. By removing these organic substances from the system sheet formation will be improved and consequently provide additional strength properties to the paper. Conclusion Talc since decades is well known as an effective control agent for pitch and stickies depositions but it provides much more positive effects. By adsorbing onto stickies surface it will help to remove stickies from the system in cleaners as well as in the flotation step. It also will help to control other organic material that may negatively influence the paper sheet properties due to its hydrophobic surface. To get the most out of this multifunctional mineral a proper analysis of the system is necessary to select the best dosage point and let the talc particles do their work for the benefit of the paper machine.

5 Talc s Multiple Functionality In The Paper Recycling Process Peter Biza, Imerys Pigments for Paper and Packaging 1

control with talc Improved removal of stickies with talc Talc s adsorption

6 The next 20 Minutes Some words about talc The structure of talc Talc s properties Talc use in the recycling process Classical pitch and stickies control with talc Improved removal of stickies with talc Talc s adsorption properties and its positive effects Summary Talc s benefits in paper recycling

7 Some words about talc

serpentine derivatives silica aluminious rocks derivatives magnesiumg sedimentary deposit

8 The Mineral Talc Hydrous Magnesium Silicate Formula Mg 3 Si 4 O 10 (OH) 2 Layered structure Group of phyllosilicates A B A structure 4 possible geological origins magnesium carbonate derivatives serpentine derivatives silica aluminious rocks derivatives magnesiumg sedimentary deposit derivatives Two main macroscopic structures Microcristalline, less lamellar Macrocristalline, M i t highlyhl lamellarll

9 Talc a layered silicate Organophilic surface Organophilic surface

10 Some special Properties of Talc Nt Naturally platy lt The softest t mineral on earth Organophilic surface properties Hydrophobic behaviour

11 Platy Morphology Microcrystalline talc High lamellar - Macrocristalline Platyness provides excellent printability especially in rotogravure printing Microcristalline talc shows high specific surface for adsorption processes

12 Softest Mineral on Earth relative ha ardness Calcite = 9 Diamond = 1600 Quartz = 100 Gypsum = 3 Talc = Mohs Hardness Softness reduces abrasion and increases wire and felt life Scale of hardness, Friedrich Mohs, 1812

13 Organophilic - hydrophobic surface Organophilic surface is responsible for the adsorption effect of talc

14 Talc Use in Paper Recycling

15 Stickies treatment with talc Various process steps where talc supports removal and pacification of stickies

How talc interacts with stickies Both have hydrophobic surfaces want to avoid contact with water By adsorbing each other they remove water from their surface and gain energy (Gibbs Free Energy)

16 How talc interacts with stickies Both have hydrophobic surfaces want to avoid contact with water By adsorbing each other they remove water from their surface and gain energy (Gibbs Free Energy) Bigger particles are surrounded by talc platelets No N more sticky surface Increased specific density Smaller particles can be adsorbed onto talc platelets surface Not available as free detrimental particles any more

17 The Pacification of Stickies Simulation of sticky deposits with a plastic beaker test shows the reduction of deposits with talc by pacification

18 Sticky removal in cleaners Talc platelets increase stickies density >50% sticky removal was achieved in a mill trial y by the effect of increased density

19 Sticky removal during flotation In a deinking line for high quality deinked pulp sticky removal during flotation could be increased from 23% to 85% using talc

waste paper Originating from additives In colloidal or dispersed

20 Organic substances in the system Numerous other organic, detrimental substances Originating from wood Originating from waste paper Originating from additives In colloidal or dispersed form Harm fibre-fibre bonding Disturb sheet formation Formation of deposits

21 Talc s adsorptive properties Organophilic talc adsorbs organic substances Positive effects on paper Improved fibre-fibre bonding Better strength properties Higher filler levels possible Increased production Energy savings Very important: Correct selection of addition point

22 Talc effect on mill productivity Effect of talc on productivity in a recycled liner mill

23 Summary

24 Talc s effects in paper recycling Increased removal of stickies in cleaners Increased removal of stickies during flotation Reduced deposits caused by stickies Control of other organic impurities resulting in Better machine runnability Improved strength properties Higher possible filler levels Energy savings

25 Thank You for Your Attention!

SPG Suppliers to the Paper Industry

SPG Suppliers to the Paper Industry Specialty Chemicals for the Paper Industry a p e r M a c h i n e S p e c i a l t y C h e m i c a l s P Pitch Control Felt Treatment Conditioning Wire Passivators Scale Control Biological Control Stickie