Evaluation of particle and fibre degradation during processing of wood plastic composites (WPC) using dynamic image analysis

Die vorliegende Arbeit wurde im Rahmen des DFG Graduiertenkollegs 1703 „Ressourceneffizienz in Unternehmensnetzwerken – Methoden zur betrieblichen und überbetrieblichen Planung für die Nutzung erneuerbarer Rohstoffe“ durchgeführt. Es wurde der Einfluss verschiedener Prozessparameter auf die Morphologie der Holzkomponente von Holz-Kunststoff-Kompositen (Wood Plastic Composites – WPC) untersucht. Die Ergebnisse wurden bereits anderswo publiziert bzw. zur Publikation eingereicht (insgesamt vier Publikationen) und werden innerhalb individueller Kapitel der vorliegenden Arbeit wiedergegeben. WPC vereinen die Eigenschaften von Holz als Füllstoff mit den Eigenschaften von Polymeren als Matrixmaterial. Aktuelle Literatur und Forschungsarbeiten wurden gesichtet, um Möglichkeiten zu identifizieren, wie WPC zu einer effizienten Ressourcennutzung beitragen kann. Die Ergebnisse zeigen, dass eine Vielzahl von Abfall- und Nebenprodukten aus Holz- und Agrarwirtschaft zur Herstellung von WPC verwendet werden kann, z.B. Sägespäne, Reststoffe aus der Plattenproduktion und Schlämme aus der Faserstoffproduktion. Darüber hinaus können auch Kunststoff-Rezyklate und Biokunststoffe als Rohstoff dienen. Für die Eigenschaften von WPC spielt die Morphologie der Holzkomponente – Fasern oder Partikel – eine entscheidende Rolle. Während der Verarbeitung von WPC treten hohe Temperaturen und Scherkräfte auf, welche zur Zerkleinerung der Holzkomponente führen. Um die Zerkleinerung während der Verarbeitung analysieren zu können, wurde die Eignung der Partikel¬charakterisierung mittels dynamischer Bildanalyse zur Größenbestimmung von WPC-Füllstoffen geprüft. Dafür wurden Holzpartikel aus der Polymermatrix gelöst und ihre Morphologie vor und nach der Verarbeitung verglichen. Es zeigte sich, dass eine Auswertung bezüglich der längenbasierten Größenverteilung am besten geeignet ist, um Prozess-Effekte zu analysieren, da Partikel an beiden Enden der Größenverteilung gut abgebildet werden. Die Effekte von Prozessparametern wie Holzanteil, Beschickungsmethode, Vorwärmen des Holzes, Polymerviskosität, Rotor-/Schneckendrehzahl, Förderrate und Schneckenkonfiguration auf die Holzzerkleinerung wurden untersucht. Dazu wurden Fichtenholz-Partikel (Picea abies) entweder unter Verwendung eines Innenmischers oder eines Doppelschnecken-Extruders mit Polypropylen (PP) compoundiert. Zur Bestimmung des Einflusses der Polymerviskosität wurden verschiedene Sorten PP und schwachverzweigtes Polyethylen (HDPE) verwendet, welche sich in ihrem Schmelzflussindex (melt flow rate – MFR) unterscheiden. Nach dem Compoundieren betrug die Partikelgröße nur noch < 3 % der ursprünglichen Größe. Bei den PP-Kompositen nahm die Partikelzerkleinerung sowohl im Innenmischer als auch im Extruder mit zunehmendem Holzanteil zu. Auch eine zunehmende Anzahl an Knetelementen im Schneckenprofil führte zu einer stärkeren Partikelzerstörung. Bei den HDPE-Kompositen war der Einfluss des Holzanteils nur gering. Wurden die Holzpartikel und das Polymer dem Prozess gleichzeitig zugeführt, war die Partikelzerstörung intensiver als wenn die Partikel dem bereits geschmolzenen Polymer zugegeben wurden. Auch ein Vorwärmen der Partikel führte zu einer stärkeren Zerkleinerung. Die Zerkleinerung konnte unter Verwendung eines Matrixpolymers mit hohem MFR reduziert werden. Zum einen variierte der Einfluss der Förderrate mit der Schneckendrehzahl, zum anderen variierte der Einfluss von Förderrate und Schneckendrehzahl auch mit dem Holzanteil. Da die Bedingungen des Compoundierprozesses im Labormaßstab üblicherweise nicht mit Bedingungen im Industriemaßstab vergleichbar sind, wurden die Prozessparameter an einem Labor-Extruder so gewählt, dass sie industrielle Bedingungen imitieren. Die Einkürzung von Kiefernholzfasern (Pinus radiata) wurde mit der Einkürzung von Glasfasern verglichen, da diese ein Standardmaterial in der industriellen Kompositfertigung darstellen. Mittels sogenannter „Dead-stop“-Versuche und Probennahme entlang der Extruderschnecken wurde der Einfluss von Schneckenkonfiguration, Schneckendrehzahl und Förderrate analysiert. Prozesseinstellungen, die einen geringeren Anteil an spezifischer mechanischer Energie ins Material eintrugen, sowie eine schonende Schneckenkonfiguration verzögerten die Fasereinkürzung entlang der Extruderschnecken. Für eingangs längere Glasfasern war dieser Effekt ausgeprägter als für eingangs kürzere Holzfasern. Die Faserlänge im Endprodukt zeigte jedoch keine Unterschiede bezüglich der Prozesseinstellungen. Glasfasern zeigten deutlichere Unterschiede in der Faserlänge aufgrund der Schneckenkonfiguration als Holzfasern. Diese spiegelten sich auch in den mechanischen Eigenschaften wieder: ein aggressiveres Schneckenprofil resultierte in geringeren Festigkeiten bei den Glasfaser-Kompositen, jedoch nicht bei den Holzfaser-Kompositen

Lean performance measures in a supply chain

Dissertação para obtenção do Grau de Mestre em Engenharia e Gestão IndustrialIn the existing global economic context it is crucial that companies understand the importance of the supply chain, so that they can maintain their respective competitive advantage. Several of the supply chain’s approaches consider the customer and the definition of value as key features. One easily associates the Lean philosophy to supply chains, with its basis of continuous improvement and elimination of waste. Companies which employ this philosophy begin with lean thinking, which highlights the customer and the definition of value. Therefore it is vital that companies identify what constitutes added value to the customer. Thus we arrive at the reasons which have led to the creation of this dissertation. The motivation concerns the small amount of data found upon reviewing the existing literature of the application of Lean philosophy to the Wood-Plastic Composite Industry (WPC). Consequently the study’s main goal is the identification of Lean performance measures. This dissertation contains concepts of Lean philosophy and strategy to provide background for its practical part, after which, we explain the applied methodology: identification of the performance measures, application of strategy analysis tools, the development of a survey and its statistical treatment and finally interviews to management. The results of the surveys have provided results which have helped identify the most important categories: time and flexibility; and the most relevant performance measures. The interviews’ results provided input on management’s knowledge and expectations of Lean, and the discovery of possible areas for improvement. The major conclusion of this study is the importance given to Lean performance measures in the WPC industry’s context, which can help in the implementation of Lean

Analysis of steep sided landfill lining systems

The EC Landfill Directive (1999), which is enforced in England and Wales through the Landfill (England and Wales) Regulations (2002), has increased the technical challenge associated with the design and construction of landfill containment systems, in particular those on steep side slopes. Increased numbers of lining system components, varied configurations, and complex loading scenarios require advanced analysis tools to facilitate design. This project involved the development of advanced numerical modelling techniques, based on the FLAC finite difference modelling code. The analysis toolbox can be used to predict the behaviour of multilayered geosynthetic and soil lining systems, during and after staged construction. The model can include non-linear interface and geosynthetic axial properties, represent complex loading, including downdrag from the waste mass, whilst retaining the flexibility to represent varied geometries and include engineered support structures. Whilst numerical modelling is becoming increasingly commonplace in commercial design, there is little evidence of the validation of numerical models with field or experimental data. Validation of the analysis toolbox described in this document was conducted by back analysis of published data, modelling of landfill failure mechanisms, and comparisons to large scale laboratory testing. Design of field scale instrumentation has also been carried out as part of this project. The influence of interface shear strength variability has been assessed through the compilation of a comprehensive database, and the effect of this variability on lining system behaviour assessed through reliability based analyses. This has shown probability of failures may be higher than proposed limiting values when adopting traditional accepted factors of safety. A key area of interest identified during the project was the requirement for support, potentially through reinforcement, of the geological barrier. The inclusion of randomly reinforced fibres in bentonite enhanced soil has shown the potential for increased strength, without adverse effects on hydraulic barrier performance. ii Additionally, the influence of geomembrane seams on lining system integrity has been investigated, showing that fusion welded seams can result in stress concentration and extruded seams can cause significant stress concentration

Active thermography for the investigation of corrosion in steel surfaces

The present work aims at developing an experimental methodology for the analysis of corrosion phenomena of steel surfaces by means of Active Thermography (AT), in reflexion configuration (RC). The peculiarity of this AT approach consists in exciting by means of a laser source the sound surface of the specimens and acquiring the thermal signal on the same surface, instead of the corroded one: the thermal signal is then composed by the reflection of the thermal wave reflected by the corroded surface. This procedure aims at investigating internal corroded surfaces like in vessels, piping, carters etc. Thermal tests were performed in Step Heating and Lock-In conditions, by varying excitation parameters (power, time, number of pulse, ….) to improve the experimental set up. Surface thermal profiles were acquired by an IR thermocamera and means of salt spray testing; at set time intervals the specimens were investigated by means of AT. Each duration corresponded to a surface damage entity and to a variation in the thermal response. Thermal responses of corroded specimens were related to the corresponding corrosion level, referring to a reference specimen without corrosion. The entity of corrosion was also verified by a metallographic optical microscope to measure the thickness variation of the specimens

Hybrid cork-polymer composites containing sisal fibre : morphology, effect of the fibre treatment on the mechanical properties and tensile failure prediction

In this study, we investigated the use of short sisal fibre with and without polyethylene-graft-maleic anhydride (PE-g-MA) as a strategy to reinforce cork–polymer composite (CPC) materials. The use of alkali treatment of sisal to improve fibre–matrix adhesion was evaluated. High density polyethylene (HDPE) was used as matrix and the composites were produced in a two-step process using twin-screw extruder followed by compression moulding. FTIR, TGA and XRD were used to confirm the sisal fibre modification. Additionally, morphology, density, diameter and tensile properties of the fibres were evaluated before processing. The hybrid composites containing cork powder (40 wt.%) and randomly distributed sisal fibres were evaluated in terms of morphology and mechanical properties. The use of a 10 wt.% sisal fibre in the presence of a 2 wt.% coupling agent based on maleic anhydride, has shown to improve the tensile and flexural properties of the composites. The higher mechanical properties were achieved by using alkali treated sisal fibres and PE-g-MA. In the presence of the coupling agent the composite morphology revealed good interfacial adhesion between the natural components and the polypropylene matrix, being in accordance with the mechanical results. Weibull cumulative distribution was successfully used to accurately predict the tensile strength failure of the hybrid CPC materials.We gratefully acknowledge to Amorim Revestimentos S.A. for the supply of cork and to Pallmann GmbH for the polymer in the grinding form. To QREN FCOMP-01-0202-FEDER-003107 financing support on the project "NovelComp". EMF acknowledge to Portuguese Foundation for Science and Technology (FCT) Grant (SFRH/BD/71561/2010)

Fatigue behaviour of FDM-3D printed polymers, polymeric composites and architected cellular materials

Polymer-based materials are increasingly produced through fused deposition modelling (FDM) – an additive manufacturing process, due to its intrinsic advantages in manufacturing complex shapes and structures at low overhead costs. The versatility of this technology has attracted several industries to print complex geometrical structures. This underlines the importance of studying the mechanical strength of FDM printed polymeric materials, especially their fatigue behaviour in cyclic loading conditions. Conventionally manufactured polymeric materials (e.g. injection moulding) have superior fatigue performance than FDM printed materials. Unlike conventionally manufactured polymers, FDM-made polymers have layer by layer adhesion and the influence of printing parameters make fatigue analysis complex and critical. The influences of printing parameters and printing material characteristics have a significant impact on the fatigue behaviour of these materials. The underlying mechanism behind the fatigue of FDM printed polymers is crucial for the assessment of these materials in structural applications. However, the fatigue behaviour of FDM printed polymeric materials has not been reviewed in detail. Therefore, this article aims to evaluate 3D printed polymeric materials’ fatigue properties. The importance of fatigue in the FDM printed biomedical materials is also reviewed, and more importantly, the novel FDM printed architected cellular material fatigue properties are also introduced. © 2020 The Author(s

Rheology and Processing of Polymers

This book covers the latest developments in the field of rheology and polymer processing, highlighting cutting-edge research focusing on the processing of advanced polymers and their composites. It demonstrates that the field of rheology and polymer processing is still gaining increased attention. Presented within are cutting-edge research results and the latest developments in the field of polymer science and engineering, innovations in the processing and characterization of biopolymers and polymer-based products, polymer physics, composites, modeling and simulations, and rheology

Tensile strength of pine and ash woods – experimental and numerical study

The mechanical properties define the behaviour of the timber under external loads, resulting directly from the timber anisotropic and heterogeneity characteristics. Depending upon the type of applied load the failure can be tensile, shear or torsion. When load enter the plastic regime, the stress-strain relationship passes through a maximum called the tensile strength. The tensile strength of wood being constant above the fibre saturation point, it increases with decreasing moisture content below the fibre saturation. This can be related to where the water is absorbed in the microstructure. Their study is of great interest allowing the rational use of different wood species for structural and building purposes