Structure-properties-processing relationships in PP-PET microfibrillar composites

This doctoral dissertation has focused on the structure-properties-processing relationships in microfibrillar composites (MFCs) prepared from polypropylene (PP) and poly(ethylene terephthalate) (PET). The MFC concept consists of three processing steps – melt blending via twin-screw extrusion, fibrillation via cold drawing, and isotropization by injection moulding or extrusion, resulting in binary composites of the higher melting temperature component being dispersed as microfibres in a matrix i.e. the lower melting temperature component. The microfibrillar structure of the reinforcement may contribute to improved mechanical properties – both stiffness and toughness. MFCs are considered an interesting class of environment-friendly fibrereinforced composites produced with conventional processing equipment and, as such, they have a large possibility to find their place in numerous applications. Although various experimental studies have been done within the field of MFCs, still, some shortcomings may be found. The development of a microfibrillar structure of the reinforcement and retaining this structure during the final melt processing step was depicted as one of the crucial factors for achieving high-quality composites, but it was not yet investigated in detail. Moreover, the influence of the fibrillation step on certain properties such as degradation and dynamic mechanical properties was not widely reported. Further on, the literature review has shown that additives and compatibilizers may play an important role in the development of the microstructure of MFCs, especially pointing out the importance of the step of production at which they are added. Overall, carefully linking the processing, their structure, with their resulting properties is essential. The research questions of this doctoral research are, therefore, as follows: i) How do the properties of MFCs change upon application of different cold draw ratios?; ii) What are the optimal processing parameters used in MFC production?; iii) What is the effect of the addition of elastomers and elastomerbased compatibilizers at different steps of the MFC manufacturing on the morphology and mechanical properties of MFCs?; and iv) Can the MFC concept be applied to novel applications such as thermoforming and the upcycling of immiscible recycled PP/PET blends? The polymers used in this research were limited to PP as matrix and PET as reinforcement, while a polyolefin based elastomer (POE) and a POE grafted maleic anhydride (POE-g-MA) were used as additives. The first part of the research focused on evaluating the influence of the fibrillation and isotropization processing stages on the development of the MFC microstructure. Fibrillation was found to be a crucial step in the production of the MFCs; therefore, different draw ratios were applied during the experimental part to define an optimal aspect ratio of the microfibres, and the results are discussed in Chapter 4. The optimal draw ratio was found to be equal to eight. Overall, the morphological characterisation proved the existence of an immiscible PP-PET blend after melt blending, and the highly oriented fibrillar state of the reinforcement component after cold drawing. Moreover, after the final isotropization step, the microscopic images showed the PET fibres were preserved and they were well dispersed within the PP matrix. Physical-chemical characterisation has shown a significant influence of the microfibrillar structure on the crystallisation and degradation behaviours of the MFCs. The crystallisation temperature of the PP component has been increased, as the PET fibres act as strong heterogeneous nucleating agents for the PP spherulites, forcing the PP lamellae to orient perpendicular to the PET fibres surface, by forming a transcrystalline layer. The positive influence of this high nucleating effect was noticed in the MFCs’ dynamic mechanical properties, as they have increased with the increment of the fibre aspect ratio. Beside the fibrillation step, in Chapter 5, the effect of different injection moulding temperatures on various properties of the MFCs was studied too. Processing the MFCs at the lowest injection moulding temperature (210 ºC) resulted in the best MFC morphologies and performances. During the experimental work of this PhD, the optimal weight ratio of the polymer components for the PP/PET blend was found to be 80/20, respectively, while 6 wt% was found as the optimum quantity for the additives. Further research was focused on the addition of elastomer-based additives into the MFCs in different stages of processing and their effect on the crystalline microstructure and mechanical properties. Fillers and additives are widely used in polymer blending, hence, Chapter 6 of this dissertation was devoted to study their influence. The main objective of this part was to evaluate the potential of adding a compatibilizer during the isotropization step and its influence on the fibrillar morphology. However, postponing the compatibilizer addition did not improve the distribution of long fibres, neither created the best mechanical properties for a compatibilized PP-PET MFC. With the addition of POE-g-MA, the fibre aspect ratio has been reduced, but the nucleating effect of the fibres was still present. Small-angle light scattering indicated a decrease in the PP spherulite size in MFC samples due to the presence of long PET microfibres, as well as in compatibilized samples, although the fibre length was affected. In addition, it was proven that the presence of POE and POE-g-MA also may act as nucleators for the PP matrix; therefore, in these MFC samples, the nucleating effect was more pronounced. Mechanical characterisation confirmed the reinforcing effect of the PET microfibres in the MFCs. Particularly, the increase in tensile modulus was noticed in non-compatibilized MFC due to the large interfacial area between the microfibres and the matrix; therefore, it was considered that some interfacial contact between the components exists, which made the stress transfer more effective. Higher values for yield strength and strain at break, as well as for impact strength, were observed for the MFC containing POEg- MA added during extrusion. Outstanding mechanical properties for this sample were achieved due to the presence of the elastomeric compatibilizer, which has enhanced the interfacial adhesion between PP and PET in the final composite, resulting in better stress transfer under the applied load. The second part of this PhD research was focused on examining novel applications for MFCs. Injection moulding as the final processing step was, for the first time, replaced by extrusion and thermoforming. Applying these two techniques has brought new insight for the production of MFCs, and opens up the possibility of using the MFC concept for producing packaging trays, eventually suitable for food packaging applications. This investigation was presented in Chapter 7 and showed that producing MFCs in the form of sheets for thermoforming could be an innovative processing method. Structural analysis has shown high aspect ratio microfibres dispersed within the matrix and possessing an excellent level of orientation. Yield strength and strain at break increased with the addition of the compatibilizer, thus, facilitating the thermoforming process. However, a real optimisation of the thermoforming process itself was not the focus of this study and remains open for further research. In the end, the feasibility of using the MFC concept to upcycle recycled materials was explored in Chapter 8. Several recycled materials such as mixed bilayer PP/PET films, polyolefins (MPO), and talc-filled PP were selected for this study and used as matrices for MFCs. Recycled MFCs were successfully prepared by the 3-step processing, although these mixtures presented significant difficulties in processability. Unfortunately, outstanding mechanical properties were not achieved for these series of MFCs; they showed little or almost no improvement compared to their recycled matrices. SEM characterisation showed a high level of PET fibre coalescence present in the MFC made out of recycled bilayer film, while in other MFCs, a large heterogeneity of the microstructure was identified. In spite of the disappointing results of these recycled MFCs, the MFC concept can still be considered an interesting approach for upcycling of mixed polymer waste and to improve the original properties of recycled materials. However, this requires further in-depth investigations, taking into account various factors such as viscosity, heterogeneity, presence of different additives, levels of degradation, etc. Overall, this doctoral dissertation presented a deep and extensive study on the MFCs concept, focusing on the relationship between structure, properties, and processing, stressing the importance of each processing parameter, as well as polymer components and additives selected for the final composition. The identified gaps within the MFC field have been covered by the experimental work and reported results. A particular contribution to the scientific world has been made by introducing a novel method for the production of MFCs, i.e., extrusion and thermoforming, and trying to upcycle different recycled mixtures. Despite the current limited commercial use of MFCs, the introduction of new environmental regulations, imposing the utilisation of certain quantity of recycled materials, as well as the recyclability of the manufactured products, may provide a boost for MFCs. The investigations presented within this dissertation have opened some new research questions and proposals for future work, which are presented at the end of this doctoral thesis

The Effect of Injection Moulding Temperature on PET Particles/Fibrils in Blends and MFCs

The microfibrillar composites of polypropylene (PP)/poly(ethylene terephthalate) (PET) have been prepared by twin-screw extrusion, followed by cold drawing. The employed stretch ratio was 4. Further processing was done by injection moulding at three different processing temperatures (210ºC, 230ºC, 280ºC) on PP/PET blends with wt% 70/30 Samples were subjected to extensive characterization in each step of MFC preparing. Fourier Transform Infrared (FTIR) spectroscopy was employed to determine the nature of the interaction between the polymers in the composites.. Thermogravimetric Analysis (TGA) were used to investigate degradation of polymers. The crystallization, melting behaviour and the crystallization morphology were investigated by Dynamic Scanning Calorimetry (DSC) and Polarized Optical Microscopy (POM). Influence of processing temperature on morphology was investigated by using Scanning Electron Microscopy (SEM). The observations from the fracture surfaces were discussed and compared with the mechanical properties, and the results have shown a significant influence of the injection moulding temperature on the morphology development and mechanical properties

The influence of draw ratio on morphology and thermal properties of MFCs based on PP and PET

The main goal of this study is to investigate the influence of draw ratio on morphology and properties in microfibrillar composites (MFCs). In situ MFCs based on polypropylene (PP) and poly(ethylene terephthalate) (PET) have been prepared at the weight ratio of 80/20 by twin-screw extrusion, followed by cold drawing and injection moulding. In order to study the differences in MFCs caused by draw ratio, the samples were prepared at different ratios and subjected to extensive characterization in each step of the MFC preparation process. The morphology of MFC and influence of draw ratio were investigated by using Scanning Electron Microscopy (SEM). The thermal decomposition of the polymers in MFCs was studied by Thermogravimetric Analysis (TGA), the melting and crystallization behaviour by Dynamic Scanning Calo-rimetry (DSC)

Morfological and electrochemical properties of LiFePO4 powders synthesized in presence of different carboxylic acids.

Predmet istraživanja ove doktorske disertacije je ispitivanje mogućnosti dobijanja prahova litijum gvožđe(II) fosfata (LiFePO4) novim i modifikovanim načinima sinteze. Zahvaljujući svojoj sposobnosti da reverzibilno interkalira/deinterkalira jone litijuma ovaj materijal se koristi kao katoda u litijum jonskim baterijama. Osnovni cilj ovih istraživanja je bio da se dobije čist materijal bez prisustva nečistoća, koji će imati pogodne fizičkohemijske karakteristike za elektrohemijsku primenu. Parametri kristalne građe mogu značajno uticati na elektrohemijske osobine, tako da je cilj istraživanja bio da se ovaj uticaj razjasni i da se sintetišu materijali koji bi u ovom smislu imali najoptimalniju morfologiju i ostale mikrostrukturne osobine. Polazeći iz vodenih rastvora, koji su se sastojali od jona litijuma, gvožđa i fosfora pomešanih u odnosu koji zadovoljava stehiometriju LiFePO4 i odgovarajuće karboksilne kiseline, dobijene su prekursorske smeše mikroemulzionom metodom, koprecipitacijom i liofilizacijom koje su dalje termički tretirane. Prekursorska smeša dobijena mikroemulzionom metodom je solvotermalno tretirana na temperaturi od 180 oC, dok su prekursorske smeše dobijene koprecipitacijom i liofilizacijom termički tretirane na visokim temperaturama (600-800 oC) u cilju dobijanja kristalnog praha LiFePO4. Korišćenjem eksperimentalnih tehnika rendgenske difrakcije na prahu, skenirajuće elektronske mikroskopije, Mesbauerove spektroskopije, rasejanja laserske svetlosti, termičke analize i elektrohemijske analize ispitan je uticaj različitih karboksilnih kiselina kao redukcionog sredstva i izvora ugljenika na morfološke i elektrohemijske karakteristike sintetisanih prahova...The subject of this PhD thesis is investigation of possibility to synthesize lithium iron (II) phosphate (LiFePO4) powders with new and modified synthesis procedures. Due to its ability to reversibly intercalate/deintercalate lithium ions, this material is used as a cathode in lithium ion batteries. The main objective of this research was to synthesize pure material without any phase impurities, which would have appropriate physical chemical properties for electrochemical applications. Crystal lattice parameters can significantly influence electrochemical properties, and this thesis aim is to clarify this relation and to synthesize materials with optimal morphology and other microstructural properties. Starting from mixed aqueous solution of lithium, phosphorus and iron ions in stoichiometric ratio and different carboxylic acids, precursors mixtures were prepared by microemulsion, coprecipitation and lyophilisation techniques, and afterwards were thermally treated. To prepare crystal LiFePO4 powders, microemulsion-derived precursor mixture was solvothermally treated at 180 oC, while precursor mixtures obtained by coprecipitation and lyophilisation were thermally treated at high temperatures (600-800 oC). X-ray powder diffraction, scanning electron microscopy, Mossbauer spectroscopy, laser light scattering, and thermal and electrochemical analyses were used to investigate the influence of different carboxylic acids as reducing agents and carbon sources on morphological and electrochemical properties of synthesized powders..

MFC concept as a possible solution for closed-loop recycling of food packaging trays

Flexible plastic films from food packaging trays make up one of the largest fractions of the plastic waste stream and recycling is one of the most important actions to deal with this fraction, reducing the impact of these plastics on the environment. However, the recyclability of multi-layered films is not straightforward and in most of the cases these fractions are landfilled or incinerated. Recycling of discarded mixed polymers without previous separation often results in low mechanical properties which have lead researchers to investigate novel solutions for recycling. In this research, the concept of microfibrillar composites (MFCs) was investigated aiming to upcycle mixed polymer waste streams. A blend based on polypropylene (PP) and poly(ethylene terephthalate) (PET) at a weight ratio of 80/20 PP/PET was studied. The final step of the MFC processing was conducted using a conical twin screw extrusion. The morphological results confirmed the presence of PET microfibrils in the composites, leading to an improvement in mechanical properties such as in the tensile yield strength and strain at break. Subsequently, the MFC samples were successfully moulded into trays via thermoforming

The feasibility of using the MFC concept to upcycle mixed recycled plastics

Several mixed recycled plastics, namely, mixed bilayer polypropylene/poly (ethylene terephthalate) (PP/PET) film, mixed polyolefins (MPO) and talc-filled PP were selected for this study and used as matrices for the preparation of microfibrillar composites (MFCs) with PET as reinforcement fibres. MFCs with recycled matrices were successfully prepared by a three-step processing (extrusion-cold drawing-injection moulding), although significant difficulties in processing were observed. Contrary to previous results with virgin PP, no outstanding mechanical properties were achieved; they showed little or almost no improvement compared to the properties of unreinforced recycled plastics. SEM characterisation showed a high level of PET fibre coalescence present in the MFC made from recycled PP/PET film, while in the other MFCs, a large heterogeneity of the microstructure was identified. Despite these disappointing results, the MFC concept remains an interesting approach for the upcycling of mixed polymer waste. However, the current study shows that the approach requires further in-depth investigations which consider various factors such as viscosity, heterogeneity, the presence of different additives and levels of degradation

Nanoparticles: Potential for Use to Prevent Infections

One of the major issues related to medical devices and especially urinary stents are infections caused by different strains of bacteria and fungi, mainly in light of the recent rise in microbial resistance to existing antibiotics. Lately, it has been shown that nanomaterials could be superior alternatives to conventional antibiotics. Generally, nanoparticles are used for many applications in the biomedical field primarily due to the ability to adjust and control their physicochemical properties as well as their great reactivity due to the large surface-to-volume ratio. This has led to the formation of a new research field called nanomedicine which can be defined as the use of nanotechnology and nanomaterials in diagnostics, imaging, observing, prevention, control, and treatment of diseases. For example, coverings or coatings based on nanomaterials are now seen as a promising strategy for preventing or treating biofilms formation on healthcare kits, implants, and medical devices. Toxicity, inappropriate delivery, or degradation of conventionally used drugs for the treatment of infections may be avoided by using nanoparticles without or with encapsulated/immobilized active substances. Most of the materials which are used and examined for the preparation of the nanoparticles with encapsulated/immobilized active substances or smart reactive nanomaterials with antimicrobial effects are polymers, naturally derived antimicrobials, metal-based and non-metallic materials. This chapter provides an overview of the current state and future perspectives of the nanoparticle-based systems based on these materials for prevention, control, or elimination of biofilm-related infections on urinary stents. It also addresses manufacturing conditions indicating the huge potential for the improvement of existing and development of new promising stent solutions

Benotung von Kindern mit Lese- und Schreibschwäche: Bewerten wir Kenntnisse oder Fähigkeiten?

Cilj je istraživanja bio dobiti procjenu stručnog suradnika logopeda o najučestalijim teškoćama u čitanju i pisanju kod učenika s disleksijom i disgrafijom (N=7) jedne osnovne škole te ispitati koliko se njihovi učitelji i nastavnici (N=9) pridržavaju općih pedagoških načela i kriterija ocjenjivanja. Rezultati istraživanja na individualnoj i skupnoj razini pokazali su da se najučestalije teškoće u čitanju i pisanju odnose na zamjene grafički sličnih slova (b-d, b-p, m-n, n-u. a-e, s-z. š-ž) i zamjene slogova (on-no, ej-je, mi-im) te teškoće u povezivanju glasova i slogova u riječi. Ispitani se učitelji i nastavnici najčešće pridržavaju pedagoških načela, odrednica i kriterija ocjenjivanja. Naglasak stavljaju na ishode i proces učenja, a ne na sposobnosti odnosno teškoće uzrokovane poremećajem. Učitelji najveću pozornost pridaju školskom ozračju (AS=4), a nastavnici postavljanju jasnih ciljeva i očekivanja (AS=3,75). Analiza rezultata pokazala je da osobni i socijalni razvoj ispitanih učenika treba više poticati, omogućiti im kontinuirano učenje socijalnih vještina te primjenjivati različite vrste praćenja, vrednovanja i ocjenjivanja jer te su kategorije najslabije procijenjene od ispitanih.The aim of this study was to obtain a speech therapist’s evaluation of the most common reading and writing difficulties of dyslexic and dysgraphic children (N=7) in one primary school, and to examine the extent to which their class and subject teachers (N=9) follow general pedagogical principles and assessment criteria. Research results on individual and group level have shown that the most common reading and writing difficulties are related to the substitution of graphically similar letters (b-d, b-p, m-n, n-u. a-e, s-z, š-ž), syllables (on-no, ej-je, mi-im) and connecting sounds and syllables into words. The interviewed teachers generally follow pedagogical principles, guidelines and assessment criteria. They place emphasis on learning outcomes and the learning process instead on abilities, or difficulties caused by disorders. Class teachers place greatest emphasis on class atmosphere (AS=4) whereas subject teachers value clear goals and expectations the most (AS=3,75). The result analysis has revealed that personal and social development of tested students needs to be encouraged more, that continuous learning of social skills needs to be enabled and various types of monitoring, evaluation and assessment applied, because these are the least favourably assessed categories by the respondents.Das Ziel dieser Studie war die Einschätzung einer logopädischen Fachkraft über die häufigsten Probleme beim Lesen und Schreiben von Schülern mit Dyslexie und Dysgraphie (N=7) einer Grundschule, sowie die Untersuchung, inwieweit sich ihre (Grundschul)lehrer (N=9) an die allgemeinen pädagogischen Prinzipien und Bewertungskriterien halten. Die Untersuchungsergebnisse auf der Einzel- und Gruppenebene haben gezeigt, dass die häufigsten Probleme beim Lesen und Schreiben im Zusammenhang mit der Verwechslung von graphisch ähnlichen Buchstaben (b-d, b-p, m-n, n-u. a-e, s-z. š-ž) und der Silbenverwechslung (on-no, ejje, mi-im) stehen, sowie mit Schwierigkeiten bei der Verbindung von Stimme und Silbe in Wörtern. Die befragten Lehrer halten sich in der Regel an pädagogische Grundsätze, Leitlinien und Bewertungskriterien. Die Betonung wird auf Lernergebnisse und den Lernprozess gelegt, und nicht auf die Fähigkeiten bzw. die durch Störungen verursachte Schwierigkeiten. Die Grundschullehrer schenken dem Schulklima die gröβte Aufmerksamkeit (AS=4), und andere Lehrer der klaren Zielsetzung und Erwartungen (AS=3,75). Die Ergebnisanalyse zeigte, dass die persönliche und die soziale Entwicklung der befragten Schüler mehr gefördert werden sollte, ihnen sollte das kontinuierliche Lernen der sozialen Kompetenzen ermöglicht werden, sowie es sollten unterschiedliche Arten der Begleitung, Evaluation und Benotung angewendet werden, denn das sind die am schlechtesten eingeschätzten Kategorien der Befragten

Specifične greške u čitanju kod dece oštećenog sluha i dece koja čuju

Reading constitutes an important segment in education and it has a direct impact on speech and language development in children with impaired hearing. Children with impaired hearing acquire through reading information that they cannot acquire through auditory way and in that way they gain new information, enrich and consolidate their knowledge. The impaired hearing, insufficiently developed speech, poor speech-language experience, narrow vocabulary, poor knowledge of grammatical and semantic elements of language, incorrect articulation, and undeveloped cognitive and linguistic function in children with impaired hearing constitute obstructions in mastering the process of reading. We formulated the problem of investigation, as well as aims and tasks directed to examination of the process of reading and detecting the deficits. We also examined impact of pupils’ age, degree of hearing impairment, achievements in mother tongue, and sex on quality of reading, mastering of reading technique and we tried to determine differences in respect to well hearing children. The investigation was carried out on the territory of Bosnia and Herzegovina (Sarajevo, Tuzla and Banja Luka) in three schools for children with impaired hearing and speech, and in one ordinary primary school in Sarajevo attended by well hearing children. The sample consisted of two groups of examinees: pupils with impaired hearing from 3rd to 8th class, N = 87 and well hearing pupils of the same age, N = 59. The Three-Dimensional Reading Test and the text under the title “Only one snowy day” were used in the investigation. The obtained results were shown tabulary and graphically. There have been noticed some irregularities and difficulties in text reading as well as arising of various errors which have made impossible to the hearing impaired pupils easy reading of a text. We have concluded that a degree of the hearing impairment and the achievement in mother tongue affect, to a great extent, a number and kind of reading errors and that a pupil’s gender affects a number and not a kind of errors and that the age hadn’t affected number or kind of reading errors in the hearing impaired children. The hearing impaired pupils had made in reading a great number of various errors which have influenced technique and affected a quality of speech and language development of a hearing impaired pupil while well hearing pupils have successfully mastered reading technique.Čitanje čini važan segment edukacije i utiče na razvoj jezika i govora kod dece oštećenog sluha. Čitanjem dete oštećenog sluha dobija informacije koje ne može dobiti auditivnim putem i time usvaja nova, bogati i utvrđuje znanja. Oštećenje sluha, nedovoljno razvijen govor, siromašna govorno-jezička iskustva, mali fond reči, nepoznavanje gramatičke i semantičke strane jezika, nepravilna artikulacija, nerazvijene kognitivne i lingvističke funkcije kod deteta oštećenog sluha otežavaju savladavanje procesa čitanja. Formulisali smo problem istraživanja, kao i ciljeve i zadatke usmerene na ispitivanje procesa čitanja i uočavanje deficita. Ispitivali smo i uticaj uzrasta učenika, stepena oštećenja sluha, uspeha iz maternjeg jezika i pola na uspešnost čitanja, ovladanost tehnikom čitanja i nastojali utvrditi razlike u odnosu na decu koja čuju. Istraživanje je sprovedeno na teritoriji Bosne i Hercegovine (Sarajevo, Tuzla i Banja Luka), u tri škole za decu oštećenog sluha i govora, kao i u jednoj redovnoj osnovnoj školi u Sarajevu, koju pohađaju deca koja čuju. Uzorak su činile dve grupe ispitanika: učenici oštećenog sluha uzrasta od III do VIII razreda, N=87 i učenici koji čuju, istog uzrasta, N=59. U istraživanju je korišćen Trodimenzionalni test čitanja i tekst “Samo jedan snežni dan”. Dobijeni rezultati prikazani su tabelarno i grafički. Uočene su nepravilnosti i teškoće pri čitanju teksta i pojava različitih vrsta grešaka, koje otežavaju čitanje učenika oštećenog sluha. Zaključili smo da stepen oštećenja sluha i uspeh iz maternjeg jezika imaju uticaj na broj i vrstu grešaka pri čitanju, pol učenika ima uticaj na broj grešaka, ali ne i na vrstu grešaka dok uzrast nije uticao na broj i vrstu grešaka pri čitanju kod učenika oštećenog sluha. Učenici oštećenog sluha su pri čitanju napravili veliki broj različitih grešaka, što je narušilo tehniku čitanja i odrazilo se na kvalitet govorno-jezičkog razvoja učenika oštećenog sluha, dok su učenici koji čuju uspešno savladali tehniku čitanja