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PROCESS INTENSIFICATION THROUGH CONTROL, OPTIMIZATION, AND DIGITALIZATION OF CRYSTALLIZATION SYSTEMSWei-Lee Wu (13960512) 14 October 2022 (has links)
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<p>Crystallization is a purity and particle control unit operation commonly used in industries such as pharmaceuticals, agrochemicals, and energetics. Often, the active ingredient’s crystal mean size, polymorphic form, morphology, and distribution can impact the critical quality attributes of the final product. The active ingredient typically goes through a series of process development iterations to optimize and scale-up production to reach production scale. Guided by the FDA, the paradigm shift towards continuous processing and crystallization has shown benefits in introducing cheaper and greener technologies and relieving drawbacks of batch processing. To achieve successful batch scale-up or robust continuous crystallization design, process intensification of unit operations, crystallization techniques, and utilizing data driven approaches are effective in designing optimal process parameters and achieving target quality attributes. </p>
<p>In this thesis, a collection or toolbox of various process intensification techniques was developed to aid in control, optimization, and digitalization of crystallization processes. The first technique involves developing a novel control algorithm to control agrochemical crystals of high aspect ratio to improve the efficiency of downstream processes (filtration, washing, and drying). The second technique involves the further improvement of the first technique through digitalization of the crystallization process to perform simulated optimization and obtain a more nominal operating profile while reducing material consumption and experimentation time. The third method involves developing a calibration procedure and framework for in-line video microscopy. After a quick calibration, the in-line video microscopy can provide accurate real-time measurements to allow for future control capabilities and improve data scarcity in crystallization processes. The last technique addresses the need for polymorphic control and process longevity for continuous tubular crystallizers. Through a sequential stirred tank and tubular crystallizer experimental setup, the control of polymorphism, particle mean size, and size distribution were characterized. Each part of this thesis highlights the importance and benefits of process intensification by creating a wholistic process intensification framework coupled with novel equipment, array of PAT tools, feedback control, and model-based digital design.</p>
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<b>PROCESS INTENSIFICATION OF INTEGRATED CONTINUOUS CRYSTALLIZATION SYSTEMS WITH RECYCLE</b>Rozhin Rojan Parvaresh (14093547) 23 July 2024 (has links)
<p dir="ltr">The purification of most active pharmaceutical ingredients (APIs) is primarily achieved through crystallization, conducted in batch, semi-batch, or continuous modes. Recently, continuous crystallization has gained interest in the pharmaceutical industry for its potential to reduce manufacturing costs and maintenance. Crystal characteristics such as size, purity, and polymorphism significantly affect downstream processes like filtration and tableting, as well as physicochemical properties like bioavailability, flowability, and compressibility. Developing an optimal operation that meets the critical quality attributes (CQAs) of these crystal properties is essential.</p><p dir="ltr">This dissertation begins by focusing on designing an innovative integrated crystallization system to enhance control over crystalline material properties. The system expands the attainable region of crystal size distribution (CSD) by incorporating multiple Mixed-Suspension Mixed-Product Removal (MSMPR) units and integrating wet milling, classification, and a recycle loop, enhancing robustness and performance. Extensive simulations and experimental data validate the framework, demonstrating significant improvements in efficiency and quality. The framework is further generalized to optimize crystallizer networks for controlling critical quality attributes such as mean size, yield, and CSD by evaluating various network configurations to identify optimal operating parameters.</p><p dir="ltr">The final part of this work concentrates on using the framework to improve continuous production of a commercial API, Atorvastatin calcium (ASC), aiming for higher yield and lower costs. This approach establishes an attainable region to increase crystal sizes and productivity. Due to ASC’s nucleation-dominated nature, the multi-stage system could not grow the crystals sufficiently to bypass granulation, the bottleneck process in ASC manufacturing. Therefore, spherical agglomeration was proposed as an intensification process within an integrated two-stage crystallization spherical agglomeration system to control the size and morphology of ASC crystals and improve downstream processing and tableting. This method proved highly successful, leading to the development of an end-to-end continuous manufacturing process integrating reaction, crystallization, spherical agglomeration, filtration, and drying. This modular system effectively addressed challenges in integrating various unit operations into a coherent continuous process with high production rates.</p>
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Crystallization and phase separation in thin film polymersJiang, Long January 2014 (has links)
Properties of polymers in thin films are distinct from those in the bulk due to the significant effects of free or substrate surfaces. The presence of a free surface allows an increased mobility of polymer chains in the near surface region, therefore, a lower glass transition temperature (T<sub>g</sub>). With this lower surface T<sub>g</sub>, a surface-specific crystallization phenomenon occurring at temperatures much lower than the bulk crystallization temperature (T<sub>c</sub>) in polymers including PET, PEN and PVOH has previously been observed. However, whether or not this surface-specific crystallization is a phenomenon observable in all crystallizable polymers is still a question. Similarly, due to this greater mobility, phase separation may also be able to take place in the near-surface region of a polymer blend at a temperature much lower than the bulk phase separation temperature. Yet, no such investigation on polymer blends has been carried out. In addition, it is interesting to study the thin-film behaviours of a block copolymer that undergoes both phase separation and crystallization and compare these with corresponding bulk behaviour. In this thesis, the thin-film crystallization behaviour of polyamide 12 (PA12) in spin-cast films is presented together with some investigation of crystallization of polyamide 6 (PA6) and polystyrene. Polystyrene and poly(methyl methacrylate) (PS/PMMA) systems are used to illustrate the phase behaviours specific to the near-surface region. Finally, the microstructural evolution in high hard block content thermoplastic polyurethane (TPU) thin films on annealing has also been investigated. These TPUs have hard segments (HS) extended by 2 methyl 1,3 propanediol (2M13PD) or 1,5 pentanediol (15PD). With its flexible chains, PA12 crystallizes during spin coating forming as-spin-cast crystals with morphology that varies with solvent evaporation rate and film thickness. Despite the as spin-cast crystals, the free surface allows secondary surface crystallization of PA12 at an annealing temperature (T<sub>a</sub>) roughly 20°C below the bulk T<sub>c</sub>. The secondary surface crystals were indicated to exist in the most stable crystalline phase of PA12. Similar secondary surface crystallization has also been observed in the PA6 films but at a higher T<sub>a</sub> due to the higher T<sub>g</sub> of PA6. In addition, surface-specific crystals have been observed in PS (semicrystalline, likely due to some stereoregularity of composition), a polymer with bulky side groups. The PS surface crystals are, however, flat-on oriented showing the important effect of side groups on the morphology or growth shape of surface crystals. The discovery of these surface crystals supports the universality of surface specific crystallization. Using fast solvent quenching, it is possible to "freeze in" a structure containing both PS and PMMA in the near surface region. On annealing, surface-specific phase behaviours (observable as pits, undulations and aggregations) confined to the near-surface region take place first at temperatures around or just below the bulk polymer T<sub>g</sub>, while bulk vertical phase separation and dewetting of PS to PMMA, forming holes, network structures and islands, occur at temperatures well above T<sub>g</sub>. This surface specific phenomenon, being a result of the free surface, should be applicable to other phase separation systems with a free surface as well. An increase in the crystallinity of PS was found to promote the phase separation process, but the free surface effect is independent of the interplay between the crystallization and phase separation. Rather than having a two-phase morphology, as was previously observed in melt-quenched bulk samples, 2M13PD extended TPU spin-cast films showed a single-phase morphology as-spin-cast. However, the HS ordering, the formation of mesophase, the melting of HS ordered regions, and microphase mixing observed in thin films are consistent with the bulk results but with slightly different transition temperatures due to spatial confinement. With a more flexible chain extender, e.g. 15PD, the hard and soft phase separation is more limited. The thin film investigations have allowed a better understanding of the microstructural evolution in these high hard block content TPUs on annealing by imaging the morphology directly. A thin-film specific phenomenon: formation of large multilayer flat-on crystals, was also observed in these TPU thin films. These crystals are initially developed from preformed aggregations and are believed to be induced by the significant substrate effect in thin films and the free surface effect.
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Application of through-vial impedance spectroscopy as a novel process analytical technology for freeze dryingArshad, Muhammad Sohail January 2014 (has links)
This study aims to validate and develop applications for a novel impedance-based process analytical technology for monitoring the attributes of the product during the entire freeze-drying process (from pre-freezing and annealing to primary and then secondary drying). This measurement approach involves the application of foil electrodes, mounted externally to a conventional glass freeze-drying vial, and coupled to a high-impedance analyser. The location of the electrodes on the outside, rather than the inside of the vial, leads to a description of the technology as a through-vial impedance spectroscopy (TV-IS) technique. The principle observation from this approach is the interfacial-polarization process arising from the composite impedance of the glass wall and product interface. For a conventional glass vial (of wall thickness ~ 1 mm and cross sectional diameter ~ 22 mm) it was shown that the process is manifest within the frequency range 101 to 106 Hz, as a single, broad band peak which spans 2-3 decades of the imaginary part spectrum. Features of the interfacial-relaxation process, characterised by the peak amplitude, C″Peak, and peak frequency, fpeak, of the imaginary capacitance spectra and the equivalent circuit elements that model the impedance spectra (i.e. the solution resistance (R) and solution capacitance (C) were monitored along with the product temperature data during the cycle(s), for a variety of surrogate formulations comprising lactose, sucrose, mannitol or maltodextrin solutions, during the freezing, re-heating, annealing and primary drying stages of freeze drying). It was shown that the parameters, fpeak and R, are strongly coupled to each other and change as a function of the temperature of the solution and its phase state, whereas C″Peak is strongly coupled to the amount of ice that remains during the drying process. Both log fpeak and log R have a linear dependence on the temperature of the solution, provided there was no phase change in the solution. The crystallization process (ice onset, solidification and equilibration to shelf temperature) is characterized well by both log fpeak and log R, whereas the parameter R demonstrates most clearly the formation of eutectic crystallization during freezing. In contrast it was the parameter C which was most sensitive to the detection of the glass transition during re-heating. During primary drying, it was shown that C″peak, is dependent on the amount of ice remaining and therefore provides a convenient assessment of the rate of drying and primary drying end point. The impedance changes during annealing provide a mechanistic basis for the modifications in ice structure which result directly in the observed decrease in primary drying times. The principal observation on annealing of a 10% w/v solution of maltodextrin, was the minimal changes in the glass transition (recorded at ~−16 °C) during the re-heating and cooling step (post-annealing). This result alone appears to indicate that a maximum freeze concentration was achieved during first freezing with no further ice being formed on annealing. The phenomenon of devitrification (and the production of more ice, and hence larger ice crystals) was therefore discounted as the mechanism by which annealing impacts the drying time. Having excluded devitrification from the mechanism of annealing enhanced drying, it was then possible to conclude that the decrease in the electrical resistance (that was observed during the annealing hold time) must necessarily result from the simplified structure of the unfrozen fraction and the improved connectivity of ice crystals that may be the consequence of Ostwald ripening. The application of through vial impedance measurement approach provides a non-invasive, real time monitoring of critical process parameters which subsequently leads to an improved understanding of the mechanisms and effects of different parameters, providing a reliable basis for process optimization, along with improved risk management to ensure optimum quality of the formulation and optimization of the freeze drying process.
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Investigation into co-crystal formation with cyclophosphazenesWahl, Helene 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This study aimed to combine the principles of crystal engineering with the properties of cyclotriphosphazene derivatives to construct supramolecular assemblies in the solid state. The ease with which the chloro substituents on cyclotriphosphazenes can be replaced makes them ideal candidates for this study. The substituents were chosen for their ability to form either hydrogen bonding interactions or halogen bonding interactions in the solid state. The cyclotriphosphazene derivatives were co-crystallised with various small organic molecules with complementary functional groups, as well as with other cyclophosphazene derivatives. The aim was to form co-crystals or solvates with these cyclophosphazene derivatives as co-crystals contain a wealth of information regarding the forces governing the aggregation of molecules in the solid state. Cyclotriphosphazenes, with their array of substituents, could broaden the range of potential interactions governing crystalline assembly.
Fifteen cyclotriphosphazene derivatives were synthesised and characterised in this study. The novel crystal structures of two cyclotriphosphazene derivatives have been elucidated by single crystal X-ray diffraction. These are 2,2-bis(4-formylphenoxy)-4,4,6,6-bis[spiro(2',2"-dioxy-1',1"-biphenylyl)]cyclotriphosphazene and hexakis(4-cyano-phenoxy)cyclotriphosphazene.
In the course of this study two novel polymorphs of hexakis(4-fluorophenoxy)cyclotri-phosphazene were identified and studied. The novel triclinic form undergoes an irreversible transformation to the previously reported monoclinic phase at high temperatures. The reported monoclinic phase, however, transforms to a monoclinic C phase in a single-crystal to single-crystal fashion. It is also suspected that this phase transformation is in fact reversible on cooling of the crystal to temperatures below -45 °C.
One novel co-crystal structure of hexakis(4-pyridyloxy)cyclotriphosphazene with terephthalic acid was identified and characterised. However, analysis of the Cambridge Structural Database indicates that co-crystal formation with cyclophosphazenes is not a commonly occurring phenomenon. This leads to the conclusion that cyclotriphosphazenes can be used in crystal engineering as supramolecular building blocks, but their shape and size tend to inhibit the formation of co-crystals. Therefore co-crystal formers have to be chosen with great care. / AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om die beginsels van kristalingenieurswese te kombineer met die eienskappe van siklotrifosfaseen afgeleides om sodoende supramolekulêre versamelings in die vastetoestand te bou. Die gemak waarmee die chloor substituente op die siklotrifosfaseenring vervang kan word, maak hierdie molekules ideaal vir hierdie studie. Die substituente is gekies op grond van hul potensiaal om waterstofbindings of intermolekulêre halogeenbindings in die vastetoestand te vorm. Ko-kristallisasie eksperimente is met die siklotrifosfaseen afgeleides en verskeie klein organiese molekules met komplementêre funksionele groepe uitgevoer, asook tussen die verskeie siklotrifosfaseen afgeleides met mekaar. Die doel was om mede-kristalle of solvate met hierdie siklotrifosfaseen afgeleides te vorm aangesien mede-kristalle ‘n magdom inligting bevat rakende die kragte wat die versameling van molekules in die vaste fase beheer. Die siklotrifosfaseen afgeleides wat ‘n wye verskeidenheid substituente kan dra, kan hierdeur die moontlike intermolekulêre interaksies wat die versameling in die kristallyne vaste fase beheer verbreed.
In hierdie studie is vyftien siklotrifosfaseen afgeleides gesintetiseer en gekarakteriseer. Die voorheen onbekende kristalstrukture van twee siklotrifosfaseen afgeleides is in hierdie studie geïdentifiseer, naamlik 2,2-bis(4-formielfenoksie)-4,4,6,6-bis[spiro(2',2"-dioksie-1',1"-bifeniliel)]siklotrifosfaseen en heksa(4-sianofenoksie)siklotrifosfaseen. Die strukture is bepaal deur enkelkristal X-straaldiffraksie.
In die loop van hierdie studie is twee voorheen onbekende polimorfs van heksa(4-fluorofenoksie)siklotrifosfaseen geïdentifiseer en bestudeer. Die nuwe trikliniese vorm ondergaan ‘n onomkeerbare faseverandering na die monokliniese vorm by hoë temperature. Die bekende monokliniese P fase ondergaan egter ‘n verdere faseverandering na ‘n monokliniese C fase. Hierdie geskied as ‘n enkel-kristal na ‘n enkel-kristal faseverandering. Daar word ook gespekuleer dat hierdie spesifieke faseverandering wel omkeerbaar is indien die kristal na -45 °C afgekoel word.
Een nuwe mede-kristal tussen heksa(4-pyridieloksie)sikotrifosfaseen en 1,3-dibensoësuur is in hierdie studie geïdentifiseer en gekarakteriseer. ‘n Analise van die Cambridge Strukturele Databasis het egter aangedui dat die vorming van mede-kristalle nie ‘n alledaagse verskynsel is in sikotrifosfaseen afgeleides nie. Dit lei tot die gevolgtrekking dat sikotrifosfaseen molekules wel in kristalingenieurswese gebruik kan word as supramolekulêre boustene, maar dat die vorm en grootte van die molekules die kristallisering van mede-kristalle verhoed. Dus moet die molekules wat saam met die siklotrifosfaseen molekules gekristalliseer wil word, goed deurdink word.
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Studying crystallization kinetics using solution crystallization analysis by laser light scattering (Scalls)Robertson, Divann 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: This study involved the analysis of crystallization kinetics by means of a unique and newly
developed Solution crystallization analysis by laser light scattering (Scalls) technique. In the main
study we compared two commercial linear low-density polyethylene (LLDPE) polymers (PE-1-
octene and PE-1-hexene) and studied the effect of short-chain branching on the solution
crystallization of these complex polymer systems. Characterization of the polymers was done by
nuclear magnetic resonance spectroscopy (NMR) and high-temperature gel permeation
chromatography (HT-GPC).
The second study involved the fractionation of a PE-1-hexene copolymer by temperature rising
elution fractionation (Tref) and analyzing the solution crystallization of the different temperature
fractions. This resulted in important details on the different molecular regions present in the
polymer.
A third additional study was done on the compatibility in polyolefin blends. Two different blends
were prepared: isotactic polypropylene (iPP) – low density polyethylene (LDPE) blend and iPP –
polypropylene impact copolymer (PPIC) blend. It was found that co-crystallization only occurred
for the iPP - PPIC blends. Phase separation occurred for the iPP – LDPE blends, resulting in the
formation of two phases for all blend compositions.
Solution crystallization analysis is usually measured by the conventional Crystallization Analysis
Fractionation (Crystaf) technique. In this study all crystallization data were compared with Crystaf
results and a good correlation was found between the results obtained by Crystaf and Scalls. The
major advantages of the Scalls technique are that, results similar to that of Crystaf can be acquired
with much shorter analysis times and Scalls also allows for the measurement of solution melting of
the crystallized polymer solutions. / AFRIKAANSE OPSOMMING: Hierdie studie het die analise van kristallisasie kinetika behels met behulp van die unieke en nuut
ontwikkelde oplossing kristallisasie analise deur laser lig verstrooiing (Scalls) tegniek. In die hoof
studie het ons twee kommersïele liniêre lae-digtheid polietileen (LLDPE) polimere (PE-1-okteen en
PE-1-hekseen) vergelyk en die effek van kort-ketting vertakking op kristallisasie in oplossing van
hierdie komplekse polimeer sisteme bestudeer. Karakterisering van die polimere was gedoen met
kern magnetiese resonans spektroskopie (KMR) en hoë-temperatuur gel permeasie kromatografie
(HT-GPC).
Die tweede studie het die fraksionering van ‘n PE-1-hekseen ko-polieer met behulp van
temperatuurstyging eluering fraksionering (Tref) behels asook die analisering van kristallisasie in
oplossing van die verskillende temperatuur fraksies. Belangrike informasie oor die verskillende
molekulêre areas teenwoordig in die polimeer was verkry.
‘n Derde addisionele studie was gedoen op die versoenbaarheid in poliolefin mengsels. Twee
verskillende mengsels was voorberei: isotaktiese polipropileen (iPP) – lae digtheid polietileen
(LDPE) mengsel en iPP – polipropileen impak ko-polimeer (PPIC) mengsel. Daar was gevind dat
ko-kristallisasie slegs in die iPP – PPIC mengsel plaasgevind het. Fase skeiding het plaasgevind in
die iPP – LDPE mengsels wat tot twee fases gelei het vir alle mengsel komposisies.
Kristallisasie in oplossing word gewoonlik gemeet met die konvensionele kristallisasie analise
fraksionering (Crystaf) tegniek. In hierdie studie was al die kristallisasie data met Crystaf resultate
vergelyk en ‘n goeie korrelasie was gevind tussen die resultate van Crystaf en Scalls. Die grootste
voordele van die Scalls tegniek is dat resultate soortgelyk aan diè van Crystaf kan verkry word met
baie korter analises en Scalls laat ook toe vir die meting van smeltpunt van die gekristalliseerde
polimeer oplossings.
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Co-crystallisation with 1,2,3,5-dithiadiazolyl radicalsRobinson, Sean Wade 03 1900 (has links)
Thesis (MSc)--Stellenbosch University, 2012. / Please refer to full text for abstract
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Co-crystallization in polyolefin blends studied by various crystallization analysis techniquesSweed, Muhamed 03 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006. / Co-crystallization is the phenomenon by which chains of different crystallizabilities
crystallize at the same temperature. Co-crystallization is frequently observed in the blends of
different types of polyethylene. It is believed that co-crystallization can occur due to the
thermodynamically miscible parts of two components in the blends having similar
crystallization rate.
The study focused on the phenomenon of co-crystallization in polyethylene blends and how
by varying the crystallization conditions the co-crystallization region will change.
Three techniques have been used in this study. TREF was used to fractionate the polymers
and blends. Each of the TREF fractions was studied using both DSC and CRYSTAF to
determine whether the fraction contained both types of materials. It is shown that the
difference in the crystallization fractionation mechanisms between TREF, CRYSTAF and
DSC can be utilize to study co-crystallization effects in polyethylene blends.
Results also shows that by varying the heating and cooling rate profiles in DSC and
CRYSTAF the co-crystallization fractions will appeared as a single fraction or as two separate
fractions. Further, it was demonstrated how the co-crystallization area could be illustrated
using a unique 3-dimensional plot where the data from the prep-TREF fractionation, and the
DSC and CRYSTAF, were combined to give the “crystallization map” of the blend. These
plots give a quiche visual illustration of any co-crystallization regions in the blends as well as
how much the crystallization conditions effect the blend crystallization.
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Investigation of the co-crystallisation of N-heterocyclesLoots, Leigh-Anne 03 1900 (has links)
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2009. / Co-crystals are excellent materials for studying intermolecular interactions in the solid-state and can be used to further our knowledge of the balance between strong and weak intermolecular interactions. The O–H∙∙∙∙∙∙Narom synthon was chosen as the focus of this investigation of hydrogen bonding motifs. The starting materials selected all have two hydrogen bond donor and/or acceptor sites for the formation of extended networks. All molecules are also aromatic such that the influence of weaker π∙∙∙∙∙∙π interactions can be included in the study. Two 3x3 grids of related co-crystals were produced from these starting materials and are reported in this thesis as part of an ongoing investigation into a broader set of co-crystals.
A part of the work describes the investigation of co-crystals prepared by the combination of related benzenediol and diazine isomers taken from a 3x3 grid. The solid-state structures of each of the six starting materials are discussed briefly to describe the nature of intermolecular interactions involved in the single component crystals. Trends in hydrogen-bonding patterns as well as the weaker interactions identified in the starting materials, can be used to recognise those in the subsequent multi-component crystals. Thirteen co-crystal compounds were obtained, of which twelve structures are novel. Each of these co-crystal structures is discussed in terms of intermolecular interactions and packing in the solid state. Hydrogen-bonding patterns and structural similarities are highlighted in related co-crystal structures as well as between co-crystals and their respective starting materials.
The combination of benzenediol isomers with benzodiazine isomers yielded seven novel co-crystal structures in a second 33 grid is reported. The structure of phthalazine, which has not yet been reported, is included in addition to these co-crystals, while the structures of quinazoline and quinoxaline that were retrieved from the CSD are discussed briefly. Co-crystal structures are discussed individually, focusing on the intermolecular interactions that are significant to the structural architecture of the compound. Certain co-crystals that display structural similarities with structures of the 3x3 grid, as well as with co-crystals presented in Chapter 3, are discussed in the relevant sections.
Lastly, two extended pyridyl diyne ligands that were synthesised for use in future co-crystallisation studies similar to those reported earlier are briefly highlighted. The crystal structures of the pure compounds and of a hydrate of one of the ligands were obtained and discussed briefly. To date only one of these structures has been reported in the literature.
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Chemical modification of polysaccharides with hydrophilic polymers for CaCO3 crystal growth modification and filler retention, for paper applicationsMatahwa, Howard 12 1900 (has links)
Thesis (PhD (Chemistry and Polymer Science))--Stellenbosch University, 2008. / Polysaccharides were modified with selected polymers via the grafting technique. Both
anionic and cationic polysaccharides were prepared. Random and crosslinked graft
copolymers were also prepared. The percentage grafting was determined by gravimetric
analysis and results were confirmed by cross-polarization magic angle spinning carbon-13
nuclear magnetic resonance microscopy (CP/MAS 13C NMR). These modified biodegradable
polymers were then used to flocculate precipitated calcium carbonate (PCC). The effects of
pH, percentage grafting, crosslinker concentration and polysaccharide concentration on PCC
flocculation were evaluated. Furthermore, the effects of anionic and cationic starch, either
added to PCC sequentially or simultaneously, on PCC flocculation were also investigated.
Generally, anionically modified starch showed excellent flocculation properties, which are
desirable for the end application of PCC retention.
The effect of polyacrylic acid (PAA) and polyacrylamide (PAM) modified cellulose fibers on
calcium carbonate crystal nucleation and growth modification was investigated. When the
heterogeneous crystallization of CaCO3 was carried out in the presence of modified cellulose
fibers the CaCO3 crystals were found to be residing on the surface of the fibers. The
morphologies of the crystallized CaCO3, polymorph and fiber surface coverage were different
for cellulose materials grafted with polymers of different functionalities, meaning that there is
interaction between the crystal growth modifier and the growing nuclei.
The effect of the modified starch on the crystallization of calcium carbonate gave useful
insight into designing CaCO3 filler morphologies. It was found that the filler size,
morphology and surface properties of fillers can be tailor-made by choosing suitable CaCO3
crystallization conditions as well as a suitable crystal growth modifier. The crystallized
CaCO3 had a negatively charged surface. Results of fluorescence studies showed that the
PAA modified starch (polymeric additive used) resided on the surface of the crystals. Thus
the presence of the polysaccharide on the surface of a filler could be advantageous for
strengthening fiber–filler bonding in paper applications.
Anionic starch materials were also used to prepare anionic-starch-coated starch particles. Both
the anionic starch and anionic-starch-coated starch particles were evaluated for PCC retention
and other properties of hand sheets. When anionic-starch-coated starch particles were used
there was generally an improvement in the PCC retention, while the other paper properties
remained desirable. The success achieved with the use of anionic-starch-coated starch
particles now opens the way for the further preparation and testing of various modified starch
particles, for optimization of filler retention.
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