瑞典专利SE1650193A1 Precipitated calcium carbonate

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The present invention relates to crystalline and stable amorphous CaCCprecipitated on lignocellulosic fibers.
公开号:SE1650193A1
申请号:SE1650193
申请日:2016-02-12
公开日:2017-08-13
发明作者:Backfolk Kaj；Heiskanen Isto；Laukala Teija
申请人:Stora Enso Oyj；
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PRECIPITATED CALCIUM CARBONATE Field of the invention The present invention relates to crystalline and stable amorphous calciumcarbonate (CaCOg) precipitated on Iignocellulosic fibers.
Background Minerals can be fixed onto Iignocellulose by various methods using modifiedpigments, by co-mixing with flocculation or fixation chemicals, or by direct orin-situ precipitation via various precursors. When calcium carbonate isprecipitated in-situ onto cellulose fibers during paper manufacturing, a uniquecomposite material is obtained. This leads to a pulp furnish and engineeredfibers with a high fi|er content (Ciobanu et. al., 2010), high fi|er retention(Ciobanu et. al., 2010; Klungness et. al. 1997; Silenius, 1996) and a moreuniform distribution of fi|er material within the sheet (Mohamadzadeh-Saghavaz et. al., 2014; Silenius, 1996), which results in improved opticalproperties without any pronounced loss of strength (Ciobanu et. al., 2010;Klungness et. al. 2000; Mohamadzadeh-Saghavaz et. al., 2014). Hence, thein-situ precipitation of calcium carbonate has gained interest in the paperindustry for high fi|er-content papers, although the full-scale implementationof the concept still poses technological challenges.
Calcium carbonate, CaCOg, can be precipitated onto fiber surfaces by thecarbonization of calcium hydroxide, Ca(OH)2, in the presence of fibers(Ciobanu et. al., 2010; Klungness et. al., 1994, 1996; Subramanian et. al.,2007) or by reactions between electrolytes that contain calcium andcarbonate (Ciobanu et. al., 2010; Kumar et. al., 2009; Mohamadzadeh-Saghavaz et. al., 2014). Conflicting results from studies on the in-situprecipitation of CaCOg together with fibers have however been presented.
Both increase in opacity (Ciobanu et. al., 2010) and increase in brightness(Mohamadzadeh-Saghavaz et. al., 2014) as well as a decrease in opacity(Klungness et. al., 1994, 2000; Kumar et. al., 2009; Mohamadzadeh-Saghavaz et. al., 2014), and decrease in brightness (Klungness et. al., 1994,1996, 2000; Kumar et. al., 2009) and a decrease in whiteness (Klungness et.al., 1996, 2000) have been reported. Similarly, some studies have shown adecrease in tensile strength or tensile index (Ciobanu et. al., 2010; Kumar et.al., 2009; Silenius, 1996), and others an increase in tensile strength(Klungness et. al., 1994, 2000; Mohamadzadeh-Saghavaz et. al., 2014),bursting strength (Klungness et. al., 1994; Mohamadzadeh-Saghavaz et. al.,2014) and tearing resistance (Klungness et. al., 1994). Some of thecontradictory results have been linked to the different materials used in theexperiments. The decreases observed in whiteness and brightness havebeen linked to a reaction between alkali and residual lignin (Klungness et. al.,1996, 2000), and the same precipitation processes have been reported toresult in different property changes for different types of fiber (Klungness et.al., 2000; Kumar et. al., 2009). Commercial precipitated calcium carbonates,PCCs, have been optimized for light scattering by tuning their crystalmorphology and particle size, whereas calcium carbonate precipitated in-situhas not been similarly controlled and optimized (Klungness et. al., 1994). ln the in absence of lignocellulosic fibers, many different ways of controllingPCC morphology and particle size have been presented in the literature,including controlling the ratio of carbonate to calcium ions (Kitamura et. al.,2002), the use of crystallization-controlling agents such as polymers (Butleret. al., 2006; Hardikar & Matijevic, 2001; Kumar et. al., 2011; Matahwa et. al.,2008; Nielsen, et. al., 2012; Jada et. al., 2007), organic acids (Vdovic & Kralj,2000), surfactants (Wei et. al., 2005) and inorganic compounds such asmagnesium carbonate (Hu & Deng, 2004), magnesium chloride (Park et. al.,2008) and sodium silicate (Kellermeier et. al., 2010). Crystallization-controlling agents are reported to affect all phases of crystal formation ofCaCOg, i.e. from nucleation and precursors to crystal growth and agglomeration (Cölfen & Antonietti, 2008). lt is currently usually claimed that CaCOg precipitation proceeds via non-classical crystallization pathways, often including amorphous calciumcarbonate (ACC) nanoparticles or liquid precursor stages (polymer-inducedliquid precursors, PlLPs). Polyelectrolytes (Cölfen & Antonietti, 2008),especially atactic low molecular weight polyacrylic acid (PAA) (Volkmer et. al.,2005), have been used as liquid CaCOg precursors. lt is suggested that thepolymers sequester calcium ions, thus creating locally high calciumconcentrations while inhibiting crystallization (Gower & Odom, 2000). As aresult, PILP droplets are formed and may aggregate on solid surfaces beforecrystallizing or forming ACC (Cölfen & Antonietti, 2008).
An interesting property of some crystallization-controlling agents is they mayinteract with functional groups of the template material, such as cellulose.This interaction is of particular interest when, for example, calcium carbonateis precipitated onto cellulose fibers, since the effect of polymeric additives in amodified precursor system is not well understood in the cellulosic fiber-Ca(OH)2-CO2 system. However, Hosoda and Kato (2011) used the controlledinteraction between carboxyl groups of PAA and hydroxyl groups on celluloseand obtained a continuous, thin calcite film on the cellulosic surfacecrystallized from a supersaturated CaCOg solution. They concluded that thethin-film formation was a combined effect of interactions between the carboxylgroups of the polyacrylic acid and the hydroxyl or amino groups in thepolymers, and the ability of PAA to inhibit crystallization in bulk solution.
The aim of this work was to clarify the role of Na-PAA, a known PlLP-inducingpolymer, in a cellulosic fiber-Ca(OH)2-CO2 batch precipitation whencontrolling the PCC particle and crystal size and shape. The precipitationconditions needed to create submicron particles and nanocrystal aggregateson the cellulose microfibers were of particular interest. The PCC particle size,morphology and shape were determined by scanning electron microscopyand the polymorphs obtained were qualified with XRD. The experiments were carried out in a batch reactor with efficient and constant mixing at room temperature.
Summary of the invention The present invention is directed to a method for preparing stable calciumcarbonate precipitated on natural fibers comprising the steps ofa) mixing water, 0 to 120 wt-% (based on the fiber weight) of at leastone highly charged anionic polymer in solution, 1-100 wt-% (basedon the total weight of the batch) Ca(OH)2 and 0.1 to 10 wt-%(based on the total weight of the batch) of natural fibers;b) feeding C02 to the mixture of step a) during stirring to obtain aprecipitation;c) drying the mixture or filtering the precipitated solids obtained in stepb). ln one embodiment of the present invention, 60-80 wt-% of Ca(OH)2 and 40- 120 wt-% of highly charged anionic polymer is used in step a). ln one embodiment of the present invention, the highly charged anionicpolymer is polyacrylic acid or a salt thereof. ln one embodiment, the highlycharged anionic polymer is sodium polyacrylic acid. ln one embodiment of the present invention, 0.5 to 5 wt-% of lignocellulosicfibers is used as natural fibers. ln one embodiment of the present invention, 0.5 to 1.5 wt-% of lignocellulosic fibers is used as the natural fibers. ln one embodiment of the present invention, 2.5 to 3.5 wt-% of lignocellulosicfibers is used as natural fibers. ln one embodiment of the present invention, the fibers used have not beensurface modified. ln one embodiment of the present invention, said fiber is selected frommicrocrystalline cellulose, microfibrillated cellulose, nanocellulose, bacteria cellulose, cellulose nanocrystals or a mixture thereof.
One embodiment of the present invention is a lignocellulosic fiber on whichcalcium carbonate has precipitated, obtainable by the method according to the present invention.
One embodiment of the present invention is amorphous calcium carbonateprecipitated on lignocellulosic fiber, characterized in that the calciumcarbonate is essentially stable in the amorphous form. ln one embodiment,said fiber has not been surface modified.
One embodiment of the present invention is amorphous calcium carbonateprecipitated on lignocellulosic fiber, wherein less than 5% of said calciumcarbonate has transitioned from amorphous to crystalline form after storing fora period of 30 days at room temperature. ln the papermaking field, PCC morphology and particle size are importantfactors governing filler performance. Morphology control is therefore animportant factor in in-situ precipitation, but, to our knowledge, little effort hasbeen made to improve PCC morphology control in cellulosic fiber-Ca(OH)2-C02 systems, and the effect of PAA has not been investigated. ln this work,in-situ precipitation of PCC onto cellulosic microfiber in the presence of PAAwas performed using a batch reactor. The reaction between carbon dioxideand calcium hydroxide was varied to give different PCC morphologiesdepending on the concentrations of microfiber and PAA. lt was demonstratedthat the morphology of the PCC particles formed on the microfiber can bealtered by changing the process parameters and the concentrations ofcalcium hydroxide and PAA.
The degree of distribution of PCC on the fiber surface with and without PAA depended on process conditions. The effect of the precipitation conditions on the PCC crystal size and size distribution was not clear since PCCnanocrystals had a strong tendency to agglomerate. The fiber concentrationin the reactor was found to be very critical, both with and without PAA, whichwas partly ascribed to the degree of supersaturation during precipitation andto the aggregation and agglomeration of CaCOg, but the concentrations ofCa(OH)2 and PAA, and the ratio of the species were also important. Thepresence of an unstable ACC phase at beginning of the precipitation wassuspected based on the behaviour of the pH and on reports in the literature.The use of high concentration of PAA revealed the probable formation of anACC compound stable for a time of many months, which was supported by acombination of SEM imaging and XRD analysis.
The lignocellulosic fiber on which CaCOg has precipitated can also be usedfor example as a food ingredient, in tooth paste or other products for personalcare, in transparent films and as an ingredient in a pharmaceutical product,including as an active pharmaceutical ingredient.
Brief description of the figures Figure 1: Drawing of the reactor used in the experiment Figure 2: CaCOg precipitated on microfiber with targeted ash of 48.2 % using A)1.0 wt-% fiber concentration and 0.5 l/min C02 feed, B) 3.0 wt-% fiberconcentration and 0.5 l/min C02 feed, C) 3.0 wt-% fiber concentration and 1.5l/min C02 feed.
Figure 3: SEM micrographs of the ash Figure 4: pH as a function of time during carbonation of samples having differentfiber concentrations Figure 5: CaCOg precipitated on microfiber in presence of PAA concentration: A)100.0 wt-% B) 3.0 wt-% and C) 1.0 wt-%. The microfiber concentration was 1.0wt-% (A), 1.0 wt-% (B), and 3.0 wt-% (C), respectively. Note that PAAconcentration is given as wt-% of fiber addition (g).
Figure 6: XRD patterns for the samples Detailed description Materials and methods The calcium carbonate was precipitated at ambient temperature (20-23 °C)using Ca(OH)2 as lime milk and C02 (AGA, purity 99.7%). A dry cellulosicmicrofiber (Arbocel UFC100, JRS), with a mean particle size of 8 umaccording to the manufacturer was dispersed in water with strong mixing.Sodium polyacrylic acid, Na-PAA (Sigma-Aldrich, M ~1800 g/mol) wasdissolved in water (2, 5 and 8 wt-%, using a concentration as low as possibleto reach the targeted concentration in the reaction batch) and diluted with water immediately prior use.
The batches were prepared by mixing water, PAA solution (if used), Ca(OH)2and fibers, in this order. The contents of the solutions and suspensions weredetermined gravimetrically with an accuracy of 10.5 g. The precipitation wasperformed in an open batch reactor equipped with mixer and inlet for C02, asshown in Figure 1. The stirring speed was set to a constant 800 rpm and theinitial batch temperature was ca. 20 °C. Changes in temperature and pH weremonitored during the experiments, and the experiments were terminated when the pH began to stabilize at a low level, usually at ca. pH 6.5.
Most of the samples were dried in oven without filtration, but some samplesmade using PAA as an additive were filtered using a polycarbonatemembrane (Whatman, 0.6 um) and rinsed with distilled water (ca. 30 °C)before drying. When the samples were rinsed, this is indicated in the text. Thedried PCC-cellulose composite samples were studied using a ScanningElectron Microscope (FEI Nova NanoSEM 450 field emission (Schottkyemitter) with a 10.0 kV accelerating voltage, 8 mm working distance and retractable concentric back scatter detector (CBS)). Ash contents weredetermined according to TAPPI standards T 211 om-02 and T 413 om-11,and thermogravimetric analysis (Mettler Toledo TGA/DSC 2) was performed on selected samples.
The morphology of the cellulose microfiber-PCC agglomerates and the size ofPCC crystal on the cellulose were determined from the SEM images. TheCaCOg polymorphs and the crystallinity of the cellulose-PCC complexes werecharacterized using x-ray diffraction (XRD measurements on a BrukerDiscover D8 diffractometer (Karlsruhe, Germany) using Cu(Kd) radiation (Å =1 .54184 nm). The XRD diffractograms were collected in the 26 range of 13°-48°. The X-ray tube was operated at 40 kV and 40 mA. For phaseidentification, a PDF-2 database (2012) was used.
The variables relevant for the precipitating nanoclusters and crystals on themicrofibers are listed and explained in Table l. Although the fiber appears tobe a non-reactive component in the precipitation reaction, it plays animportant but indirect role in the supersaturation of the solution, in addition toits ability to assist nucleation. This is explained as follows: The Ca(OH)2/fiber ratio at a given ash content and a given amount of fiber isdecided by the targeted filler content of the fiber-PCC composite materialaccording to the following equation, derived from the T 211 om-02 ashdefinition in TAPPI. _ ÅSflfš/o mCMÛHh - 'lg-Al - 0.7402 100- AshP/tu Where A is the weight of ash targeted PCC ash, and B is the weight of the testspecimen so that B-A is the weight of fiber. The constant 0.7402 is the ratio ofthe molar masses of Ca(OH)2 and CaCOg, to translate the targeted weight ofPCC ash to the weight of Ca(OH)2. ln the batch system used, increasing fiber concentration increases Ca(OH)2concentration when the targeted ash content is kept at constant. An increase inCa(OH)2 concentration can in turn affect the degree of supersaturation and theratio of ionic species by offering reactive material for the precipitation. Animportant consequence is that when the "same" batch process is used fordifferent targeted fi|er ash contents by simply changing the amount of addedCa(OH)2 and perhaps the C02 feed, the PCC properties and thus the fiber furnishproperties may change. Even if all the process parameters were changed so thatthe ratios were truly fixed, the precipitation process would still change with achange in the amount of Ca(OH)2 added, as the driving force for precipitation issupersaturation that under given conditions depends on the concentration of theprecipitating species. Changing the fiber concentration in order to fix the Ca(OH)2concentration would, instead, change the surface area of fiber per volume unit.
Table I: Variables investigated and units used. Ratios are calculated using theunits given in the table.
Variable Clarification Ca(OH)2 concentration Calcium hydroxide concentration in reaction mixture(wt-%, of batch before precipitation) Microfiber concentration in reactionmixture (wt-%, of batch before precipitation) Microfiber concentration C02 feed Carbon dioxide feed (l/min, at 20°C) PAA concentration Concentration of additive (PAA) (wt-%, of fiber) Ca(OH)2/CO2 Ratio of calcium hydroxide concentration to carbon dioxide feed(wt-%/l/min) Ca(OH)2/fiber Ratio of calcium hydroxideconcentration and fiber concentration,(wt-%/wt-%) PAA/Ca(OH)2 Ratio of additive concentration tocalcium hydroxide concentration (wt- %/wt-%) Results and discussion Effect of microﬁber concentration and C02 feed CaCOg was precipitated onto microfibers without polymeric additives at 5different fiber concentrations, viz. 0.5, 1.0, 2.0, 3.0 and 6.0 wt-%. Thetargeted Ca(OH)2 concentration was 69 wt-% based on oven-dry fiber. Theprecipitation gave on average 46.3 wt-% ash (mineral filler) content measuredon unfiltered samples. ln this case, mineral filler content and ash content aresynonym, since microfiber gave no ash. The obtained ash gave a 91 mol-%conversion efficiency of Ca(OH)2, based on weight loss (TAPPI standards T211 om-02 and T 413 om-11 in conjunction) assuming that the lime milk wasessentially free from impurities or reaction products such as CaCOg.
Figure 2 shows relatively large PCC particles precipitated onto the at 1.0 and3.0 wt-% microfiber concentrations. The size of the deposited PCC particleswas found to decrease with decreasing ratio of fiber (wt-%) to carbon dioxide(l/min), and with increasing fiber concentration at constant ratio. Figure 2Cshows that a substantially larger fraction of nanoparticles were nucleated andgrown on the surface of the cellulose microfibers (instead of ellipsoidalCaCOg particles) at the higher fiber concentration and greater carbon dioxidefeed, presumably because of the larger surface area of fiber per unit volumeand the higher degree of supersaturation in the system.
Much of the difference in observed PCC particle sizes was due to aggregationand agglomeration of nano-sized crystals that form ellipsoidal particles at lowmicrofiber concentrations, rather than to the size of individual crystals. Whenthe fiber concentration was increased from 1.0 wt-% to 3.0 wt-% at a constantC02 feed (0.5 l/min), the morphology of the PCC particles was slightly alteredand many of the particles precipitated onto the microfibers were larger (seeFigure 2B), which is attributed to more intensive agglomeration. Moreover, 11 increasing the C02 feed from 0.5 I/min to 6.0 I/min for the suspensioncontaining 0.5 or 1.0 wt-% microfiber did not lead to any detectable change inthe morphology of the PCC particles. lnstead, when the C02 feed wasincreased in batches containing 3.0 wt-% or more fiber, the crystal sizedecreased as can be seen in Figures 2B and 2C. Changes in aggregationand agglomeration resulted in a more even PCC distribution on the fibersurface and a better coverage of the fiber. Figure 3 shows SEM images ofash (525i25°C) of sample precipitated using 3.0 wt-% fiber concentration and 1.5 I/min C02 feed, with irreguiar PCC aggiomerates. ln experiments conducted by Subramanian et al. (2007), ellipsoidal PCCstructures were obtained, which are in agreement with Figures 2A and 2B.These ellipsoidal PCC structures, denoted co|oida| PCC (c-PCC) bySubramanian et al. (2007), were obtained with a low concentration ofcellulosic fines and were ascribed to the intermediate formation of ACC andits decomposition. This nucleation and crystal growth process led to a steepdrop in pH (formation of ACC), immediately following by a rapid increase inpH (decomposition of ACC), and this was also observed in the present case.
Figure 3 shows SEM micrographs of the ash obtained from the microfiber-PCC-PAA samples combusted at 525125 °C. The PCC particle morphologywas similar to that of PCC precipitated onto microfiber in the absence of PAA.At low PAA/Ca(0H)2 ratios, PCC particles were uniform in size with asymmetrical, spherical or ellipsoid morphology. With increasing PAA/Ca(0H)2ratio, the particles became non-uniform, developing a “molten” appearancelinked with liquid precursors of CaC03 (Gower & 0dom, 2000). Especially at50 and 100 wt-% PAA concentrations, the particles formed largepolycrystalline aggregates with curved shapes, also linked with the formationof crystals via PlLPs and ACC (Gower & 0dom, 2000).
When, at a PAA concentration of 3.0 wt-%, and the addition of Ca(0H)2 wasincreased from 32 to 69 wt-%, no obvious differences were seen in the PCC particles on the microfibers. The morphology of the particles determined after 12 combustion, on the other hand, showed an increase in particle regularity withincreasing Ca(OH)2 concentration above 41 wt-%. The particle irregularityincreased when the PAA/Ca(OH)2 ratio increased, which agrees with resultspresented by e.g. Yu et al. (2004) who concluded that PAAlCaCOg ratio has amore pronounced effect on the CaCOg morphology than on the concentrationof the CaCOg formed.
Figure 4 shows the pH as function of time upon C02 dosage and subsequentcarbonation and its dependence on the fiber concentrations. At low fiberconcentration, the pH dropped quite rapidly with a constant C02 feed at thebeginning of the experiment, followed by an immediate increase. Theinflection point occurred later with increasing fiber concentration (when the targeted ash content was kept at constant).
The effect of Sodium Polyacrylic Acid (PAA) as precursor stabilizer The use of PAA to control CaCOg crystal morphology has been previouslydemonstrated (Huang et. al., 2007; Ouhenia et. al., 2008; Yu et. al., 2004),and also when CaCOg crystals were deposited on a cellulosic substrate(Hosoda & Kato, 2001; Matahwa et. al., 2008), but, to our knowledge, effectof PAA in a cellulosic fiber-Ca(OH)2-CO2 system has not been investigated before.
Experiments with PAA carried on using three different fiber concentrations,viz. 1.0 wt-%, 3.0 wt-% and 6.0 wt-%, with a fixed ratio of fiber to C02 of 0.5.The effects of PAA and Ca(OH)2 concentration were thus varied in order todetermine their impact on the complexes obtained.
The results, summarized in Table ll and Figure 5, show that at a microfiberconcentration of 1.0 wt-% and a Ca(OH)2 concentration of 69 wt-%, anincrease in PAA concentration initially resulted in an increase in PCC particle size. The SEM images (Figure 5) show that this was due to increased 13 agglomeration and nanoparticle cluster formation. The ability of PAA to inhibitnucleation in bulk solution may have contributed to this process by supportingaggregate growth. The PCC particles formed were elongated and had a rice-like shape (PAA concentration 0.5 wt-%), similar to those seen in Figure 5 C,but slightly larger. At PAA concentrations 1.0 and 3.0 wt-%, the PCC crystalswere rounder, see Figure 5 B. The difference was probably caused bytemporary ACC stabilization by PAA, but this was not confirmed. Matahva etal. (2008) obtained similar CaCOg particles when precipitating in presence ofPAA, and these were ascribed to an ACC-PAA gel similar to that obtained byUlöinas et al (2007). They describe the formation of a viscous ACC geltemporarily stabilized by PAA, which precipitates into more stable polymorphsafter losing its stability.
Surprisingly, the effect of PAA at a microfiber concentration of 3.0 wt-% wasopposite to that at 1.0 wt-%. With increasing dosage of PAA from 0.3 to 3.3wt-%, the PCC crystal size increased, and crystals became elongated. Thecrystals retained their elongated shape but the crystal size increased whenthe PAA concentration was increased further. At very low and fixed PAAconcentrations (0.06 wt-%) and a microfiber concentration of 3.0 wt-% anincrease in Ca(OH)2 from 32 wt-% to 69 wt-% led to a significant decrease inthe PCC crystal particle size. A clear crystal phase transition region was seenat a Ca(OH)2 concentration between 51 wt-% and 69 wt-%, where the particlemorphology changed from approximately 1 micron roundish crystals to moreelongated PCC crystals with a greater aspect ratio (length ca. 1 um and width0.2 um). At 32 wt-% Ca(OH)2 addition, the crystals were more elongated at amicrofiber concentration of 6.0 wt-% than at 3.0 wt-%. An increase inmicrofiber concentration from 3.0 to 6.0 wt-% resulted in a crystal phasetransition region between 32 wt-% and 51 wt-% of Ca(OH)2 addition.
However, when the concentration of PAA was increased to 10.0 wt-%, it wasfound that the particle size and amounts of large PCC crystals and clusteredPCC agglomerates deposited on the microfibers decreased significantly, but that a few individual nano-sized PCC crystal particles were still formed and 14 present on the microfiber surface (not shown here). Figure 5 A shows thatwhen the PAA concentration was increased further to 100.0 wt-%, crystalformation of PCC on the surface of the microfiber was inhibited, which was confirmed by a lower ash content in samples rinsed before drying.
The ash contents of the some of microfiber-PAA-CaCOg complexes (rinsedbefore drying) were clearly lower than unreacted Ca(OH)2 should yield. Thiscan only be explained by the removal of soluble compounds or nanocrystalsin bulk solution during filtering of the samples through the 0.6 um membraneand subsequent rinsing. A pronounced loss of crystalline material duringfiltration should mean that an increased dose of PAA would facilitate bulksolution precipitation, instead of decreasing it as stated frequently in the literature (Hosoda & Kato, 2001; Huang et. al., 2007; Watamura et. al., 2014).
A possible alternative is heterogeneous nucleation in bulk solution, improvedby PAA addition in a manner similar to that in which the addition of PAA canimprove crystallization on cellulosic fibers, i.e. via electrostatic interactionbetween calcium ions and anionic groups of the polyelectrolyte (PAA) andforeign particles. Bulk solution precipitation is not, however, supported by thefiltrate collected in these experiments, since the filtrate was transparent,which suggests an absence of crystalline material and the presence ofamorphous transparent ACC as reported in the literature (Gower & Odom,2000; Saghavaz et. al., 2013), or a complex. The formation of an electrostaticcomplex between carboxyl groups and calcium ions is frequently described inthe literature (Hosoda & Kato, 2001; Huang et. al., 2007; Ouhenia et. al.,2008; Ulöinas et. al., 2007; Watamura et. al., 2014), and ascribed to theformation of an ACC-containing gel (Matahwa et. al., 2008; Ulöinas et. al.,2007), suggesting that role of the PAA in the system is the stabilization ofACC or the formation of a precursor or complex, or both.
Table ll: Results of the PCC-PAA-Microfiber experiments. PAA concentrationis given as wt-% of the fiber content.
Microfiber Ca(OH)2 PAA PCC morphology and sizeconcentration addition concentration[wt-%] [wt-%] [wt-%]Low PAA High PAAconc. conc.1 69 0.1; 0.5; 1.0; Eiongated. Round,3.0; 10.0; irregular Reducedparticle size32; 41; 51; 3.0 Elongated Elongated-60; 69 irregular3 69 0.3; 1.0; 2.0; Round Elongated3-3 lncreasedparticle size32; 51; 69 6.0 Slightly Eiongatedelongated Reducedparticle size6 32; 51 1.0 Elongated Reducedparticle sizeXRD and TGA Ten Microfiber-PCC samples, with and without precipitated calciumcarbonate, were characterized using XRD. Diffractograms were collected inthe 20 range of 13°-48°. XRD patterns are shown in Figure 6 and summarized in Table lll.
Figure 6 shows different crystalline forms of ce|u|ose, with s|ight peak shiftsbetween some of them. The main peak for cellulose located at 20-22°(Haleem et. al., 2014; Obi et. al., 2014; Tibolla et. al., 2014) was found insamples 0, 5 and 6, where it is quite sharp, but the calcite peak located at the same angle makes it difficult to reliably determine the presence of crystalline 16 cellulose in the samples. However, a smaller peak originating from celluloseat 34.6° was clearly observed in all the diffractograms except those forsamples 1 and 3. The presence of cellulose lß in these two samples wastherefore considered as possible. ln the case of the fiber reference sample,the co-existence of cellulose Id and cellulose lß was suspected.
The only CaCOg polymorph observed in the samples was calcite, althoughsome PAA with different molecular weights have been linked with theformation of aragonite in the literature (Ouhenia et. al., 2008; Watamura et.al., 2014). Calcite peaks (Kim, et. al., 2013; Kirboga et. al., 2014; López-Periago et. al., 2010) were observed in all samples except for the 0 (the fiberreference) and 5 and 6 (Ca(OH)2 69 wt-%, C02 feed 0.5 l/min and PAAconcentrations 50.0 and 100.0 wt-%). The ash contents (525i25°C) forsamples 5 and 6 were 8.2 and 4.0 %, respectively, confirming that samples 5and 6 clearly contained sufficient ash to be detectable in the XRDmeasurement, i.e. if it were crystalline.
For sample 5 and 6, the absence of both crystalline Ca(OH)2 and crystallineCaCOg suggests that the high PAA concentration in the samples led to theformation and stabilization of amorphous CaCOg. The unstable character ofamorphous ACC is well known, but no phase transition to a crystallinematerial detectable with XRD was observed, despite the long delay timebetween the precipitation experiments and the XRD measurements, eventhough particulate matter residing on the fibers was observed with SEM andthe ash content of the samples showed that the concentration of inorganicswas detectable with XRD, if crystalline. 17 Table lll: XRD results.
Sample number and description Cellulose I PCCFiber reference 0 - Microfiber, d, ßuntreatedNo PAA 1 -fiber 1 wt-% ß (possible) CalciteC02 feed 0.5l/min2 -fiber 3 wt-% ß CalciteC02 feed 0.5l/min3 -fiber 3 wt-% ß (possible) CalciteC02 feed 1.5l/minCa(0H)2 69 wt-% 4 - PAA 1.0 wt-% ß CalciteC02 feed 0.5”min 5 - PAA 5Û.O Wt- ß _%6 - PAA 100.0 wt- ß _%PAA 3.3 wt-% 7 - Ca(0H)2 32 ß Calciteco2 feed 0.5 Wl-%l/min _8 - Ca(0H)2 51 ß Calcitewt-%9 - Ca(0H)2 69 ß Calcitewt-% Table IV shows the results of the Thermogravimetric measurements. The data at550°C and 925°C were used to estimate the Conversion yield and possibleresidual Ca(0H)2.
Table IV TGA results 18 Property Method/basis unit 11 2 s 5 6 102 113Dry TGA(105°C) 0/ 98.2 97.72 97.97 94.87 97.48 98.02 98.06matter °(105 °C)Ash TGA(550°C) % 43.4 29.8 44.5 7.4 35.9 43.9 44.7content(550°C)Ash TGA(550°C) %, 44.2 30.5 45.5 7.8 36.9 44.8 45.6content _drybas|s(550°C)Ash TGA(925°C) 0/ 25.9 17.3 25.8 4.6 20.5 25.4 25.9content °(925 °C)Ash TGA(925°C) %, 26.4 17.7 26.4 4.9 21.0 25.9 26.4content _drybas|s(925 °C)[CaCO3] Theoretical %, 40.6 29.0 43.4 6.6 36.0 43.0 43.8(TGA 550 and dry basis925 °C)[CaCO3] Theoretical %ofash 91.8 95.3 95.5 85.2 97.6 96.1 96.0(TGA 550 and (550 °C)925 °C)[Ca(OH)2] Theoretical % 4.8 1.9 2.7 1.5 1.2 2.3 2.4(TGA 550 and dry basis925 °C)[Ca(OH)2] Theoretical % 10.6 6.2 5.9 18.7 3.1 5.1 5.2inorganicspecies 1 Not taken at the end of the process and therefore holds a larger proportionof Ca(OH)22 Microfiber concentration 3 wt-%, PAA concentration 1.0 wt-% 3 Microfiber concentration 3 wt-%, PAA concentration 0.3 wt-% The results indicate that all the samples contained unreacted Ca(OH)2, the amount of Ca(OH)2 in the samples being typically ca. 5 wt-% of the inorganic species, with the notable exception of sample 5 which was formed in the presence of a high PAA concentration of 50 wt-%. The result is approximately 19 in line with the Conversion estimate from the TAPPI ash contentmeasurements. The remaining Ca(OH)2 was not, however, identified in theXRD analysis, suggesting either that the material was not crystalline or that itresided in CaCOg particles or microfibers, too far from the particle surfaces tobe determined by the method. On the other hand, the TGA results may alsointerfere with the release of physisorbed water at 525°C and at highertemperature the possible dihydroxylation of Ca(OH)2 (Renaudina et. al.,2008). ln view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art.However, it should be apparent that such other modifications and variationsmay be effected without departing from the spirit and scope of the invention.
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权利要求:
Claims (1)
[1] 1. Claims _ Method for preparing stable calcium carbonate precipitated on natural fibers comprising the steps of d) mixing water, 0 to 120 wt-% (based on the fiber weight) of at leastone highly charged anionic polymer in solution, 1-100 wt-% (basedon the total weight of the batch) Ca(OH)2 and 0.1 to 10 wt-%(based on the total weight of the batch) of natural fibers; e) feeding C02 to the mixture of step a) during stirring to obtain aprecipitation; f) drying the mixture or filtering the precipitated solids obtained in stepb). _ Method according to claim 1, wherein 60-80 wt-% of Ca(OH)2 and 40- 120 wt-% of highly charged anionic polymer is used in step a). _ Method according to claim 1 or 2, wherein the highly charged anionic polymer is polyacrylic acid or a salt thereof. _ Method according to claim 1 to 3, wherein 0.5 to 5 wt-% of lignocellulosic fibers is used as natural fibers. _ Method according to claim 4, wherein 0.5 to 1.5 wt-% of lignocellulosic fibers is used as the natural fibers. _ Method according to claim 4, wherein 2.5 to 3.5 wt-% of lignocellulosic fibers is used as natural fibers. _ Method according to any one of claims 1 to 6, wherein the fibers used have not been surface modified. _ Method according to any one of claims 1 to 7, wherein said fiber is selected from microcrystalline cellulose, microfibrillated cellulose,nanocellulose, bacteria cellulose, cellulose nanocrystals or a mixturethereof. _ Lignocellulosic fiber on which calcium carbonate has precipitated, obtainable by the method according to any one of claims 1 to 8. 26 10.Amorphous calcium carbonate precipitated on Iignocellulosic fiber,characterized in that the calcium carbonate is essentially stable in theamorphous form. 511.Amorphous calcium carbonate precipitated on Iignocellulosic fiberaccording to claim 10, wherein said fiber has not been surfacemodified.10 12.Amorphous calcium carbonate precipitated on Iignocellulosic fiber according to claim 10 or 11, wherein less than 5% of said calciumcarbonate has transitioned from amorphous to crystalline form afterstoring for a period of 30 days at room temperature.

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同族专利:

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JP2019511443A|2019-04-25|

CA3010703A1|2017-08-17|

KR20180114024A|2018-10-17|

US10927505B2|2021-02-23|

WO2017137941A1|2017-08-17|

SE540790C2|2018-11-13|

US20190063000A1|2019-02-28|

CN108699774A|2018-10-23|

EP3414395A1|2018-12-19|

CN108699774B|2021-12-14|

引用文献:

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US5679220A|1995-01-19|1997-10-21|International Paper Company|Process for enhanced deposition and retention of particulate filler on papermaking fibers|

FI100729B|1995-06-29|1998-02-13|Metsae Serla Oy|Filler used in papermaking and method of making the filler|

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CN105007925A|2013-02-11|2015-10-28|艾玛菲克有限公司|Amorphous calcium carbonate for accelerated bone growth|SE538770C2|2014-05-08|2016-11-15|Stora Enso Oyj|Process for making a thermoplastic fiber composite material and a fabric|

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优先权:

申请号 | 申请日 | 专利标题

SE1650193A|SE540790C2|2016-02-12|2016-02-12|Calcium carbonate precipitated on natural fibers and method for the production thereof|SE1650193A| SE540790C2|2016-02-12|2016-02-12|Calcium carbonate precipitated on natural fibers and method for the production thereof|

CN201780010039.3A| CN108699774B|2016-02-12|2017-02-10|Precipitated calcium carbonate|

KR1020187022304A| KR20180114024A|2016-02-12|2017-02-10|Precipitated calcium carbonate|

PCT/IB2017/050741| WO2017137941A1|2016-02-12|2017-02-10|Precipitated calcium carbonate|

EP17707671.8A| EP3414395A1|2016-02-12|2017-02-10|Precipitated calcium carbonate|

US16/076,976| US10927505B2|2016-02-12|2017-02-10|Precipitated calcium carbonate|

CA3010703A| CA3010703A1|2016-02-12|2017-02-10|Precipitated calcium carbonate|

JP2018541131A| JP2019511443A|2016-02-12|2017-02-10|Precipitated calcium carbonate|

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