Biocomposite of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), wood fibres and additives: physicochemical properties and processability through different techniques

In this study, biodegradable biocomposites based on polylactide with basalt fibres (BFs) or wood fibres (WFs) of 7.5 or 15 wt% were prepared by injection moulding. Various tests, including tensile test, bending test and impact test, were carried out to investigate the mechanical properties of the composites. Additionally, the samples were tested at different temperatures. Depending on the type of fibre, differences were noted in their mechanical properties; the addition of WF caused a decrease in strength and the higher the fibre content, the higher the decrease was noted from 18% up 25% in the case of tensile strength. However, the Young modulus was improved by 45% for composites with 15 wt% of WF. The addition of BF improved all the properties, especially Young modulus was improved by over 45%. Despite the low strength observed in neat polylactide at high temperatures-394 MPa, the addition of WF or BF improved the flexural strength more than twofold up to 1684 MPa (PLA/15BF). Moreover, the addition of natural fibres caused an increase in dimensional stability as shown by the decrease of the coefficient of thermal expansion which dropped over 50% for composites with 15 wt% of BF, which significantly expands the areas of use of materials. After 4 weeks of biodegradation, only a slight decrease approximately 5% was observed in the mechanical properties together with an increase in crystallinity. Overall, the results confirm that the prepared composites can be successfully used in engineering applications with long-term operation.

Properties and structure of poly(3-hydroxybutyrate-co-4-hydroxybutyrate)/wood fiber biodegradable composites modified with maleic anhydride

The utilisation of bio-based materials as a construction material presents diverse and under researched challenges that can reduce carbon emissions and improve the hygrothermal performance of buildings. Within the United Kingdom (UK), the residential construction typology of housing is vast. Just within pre-1919 dwellings, energy costs are over 70% higher by comparison to the post-1990 equivalents. This thesis intends to provide tools to effectively optimise bio-based composites for hygrothermal conditions improvement in housing and whilst the composite has been optimised for UK conditions, the impacts of this thesis is versatile and can be applied across the world for example with other construction typologies, building materials and use. This research work can provide relevant information on tailoring bio-based materials whenever indoor hygrothermal conditions are crucial for energy efficiency and comfort of building users, either in the UK, Europe or across the world. Within the scope of this work, this thesis will aim to optimise the transport of water through bio-based earth mortar composites to be used in residential properties for relative humidity moisture management. Initially, the hygrothermal performance of 11 different bio-based and recycled raw materials was analysed (four different types of (Sheep and recycled) Wool insulation, Hemp, Wood Wool Board (WWB), Saw Mill Residue (SMR), Wood Fibre (WF), Straw, Insulated Cork Board (ICB) and Polyethylene terephthalate (PET). with particular focus on Moisture Buffering Value (MBV). The best 6 performing materials were retested and analysed. It was found that the differences in MBV were negligible and this value alone was not enough to be able to ascertained which material should be selected. A new methodology of understanding the shape of the adsorption and desorption curves and then grouping this would give a better assessment of the material performance. Earth-lime mortar panels were created using locally sourced material from Liverpool (NW England) and the previous bio-based fibres. Performance analysis of the bio-based composites was done at steady and transient states for hygrothermal optimisation of the panels. Prismatic, 0.1m2 x 0.1m2 squares and disc shaped samples were cast and samples were exposed to cyclical step changes in relative humidity at 75% for 8 hours and 53% for 16 hours at 23oC, in order to mimic a UK household occupancy. Results demonstrate that an optimised mix improved thermal properties if Saw Mill Residue (SMR) is added. Further to this, traditional, thermal method of analysis (using Thermogravimetry Analysis (TGA), Differential Thermogravimetry (DTG) and Differential Scanning Calorimetry (DSC)) has been for heritage and forensic investigation of the constituent elements of the material rather than a comparison with regards to their hygrothermal performance. The best performing bio-based composite was Mix 1 SMR with an MBV of 1.26 (g/(m2 %RH)) and Water Vapour Permeability (WVP) of 2.5 (x10-11) (kg.m-1.s-1.Pa-1). Latent heat generated in the bio-based composites was explored and analysed to consider the effects within a dynamic hygrothermal environment. Heat energy is released due to the change in state of water molecule from liquid to vapour (and vice versa) due to the latent heat of vapourisation and condensation. The latent heat of both raw bio-based fibres and when combined into an earth mortar matrix was identified, analysed and is consistently demonstrated even after 21 cycles of 24 hours. After these cycles, the mix design with Wool 2 produced the greatest sustained quantity of heat generated with samples temperature increase of 1.59oC during adsorption and 0.97 oC during desorption phase. The movement of water molecules in and out of samples was researched on a physicochemical basis and organic chemistry analytical techniques were utilised to gain a better understanding of the function and important on the hydroxyl group for hygrothermal performance. Utilising analytical chemistry and thermal methods of analysis for samples conditioned at different RH, can give a greater understanding of a building materials hygrothermal properties.

Additive manufacturing techniques have made it possible to create open-cell porous structures with arbitrary micro-geometrical characteristics. Since a wide range of micro-geometrical features is available for making an implant, having a comprehensive knowledge of the mechanical response of cellular structures is very useful. In this study, finite element simulations have been carried out to investigate the effect of structure unit cell type (cube, rhombic dodecahedron, Kelvin, Weaire-Phelan, and diamond), cross-section type (circular, square, and triangular), strut length, and relative density on the Young's modulus, shear modulus, yield stress, shear yield stress, and Poisson's ratio of open-cell tessellated cellular structures. It was desired to see whether or not and to what extent each of the aforementioned parameters affect the mechanical properties of a porous structure. It was seen that the strut cross-section type does not have a considerable effect on the structure Young's modulus while its effect on the structure yield stress is significant. The strut length was not effective on the mechanical properties if the relative density was kept constant. It was also observed that the structure unit cell type and relative density have a considerable effect on the elastic properties. The highest and the lowest stiffness and strength belonged to the cube and diamond unit cell types, respectively. The rhombic dodecahedron structure with circular cross-section had a high yielding strength (second among all the cases) while its Young's modulus was relatively low. Therefore, it is the best choice for applications with low stiffness requirements, such as biomedical implants. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 386-398, 2018.

Wood flour (WF)-reinforced cis-1,4-isoprene rubber (CIR) composite was prepared through a melting process. Maleic anhydride (MAH), dicumyl peroxide (DCP), and zinc oxide (ZnO) were added to the com- posites to enhance their tensile properties and dimensional stability. The dependence of MAH, DCP and ZnO concentration at various pressing time on tensile strength, elongation at break, Young's modulus, water absorption (WA) and thickness swelling (TS) of WF-CIR composites were examined. The tensile strength, elongation at break, and Young's modulus of the WF-CIR were greatly influenced by MAH content and pressing time. The higher the MAH cocentration and the longer time were applied, the greater improvement of tensile strength, Young's modulus, water absorption and thickness swelling parameters were obtained. However, the elongation at break was found to decrease with addition of MAH. DCP and ZnO concentration were also influenced the tensile strength, elongation at break and Young's modulus for WF-CIR composites.

The current study focused on improving the properties of polylactic acid (PLA) for wider application in load-bearing scenarios. Various methods were explored to optimize the interaction between PLA and natural fibers, particularly wood fibers (WFs). Alkalized and epoxy-impregnated WFs were evaluated against untreated WFs and cellulose fibers in both injection molding (IM) and fused deposition modeling (FDM). FTIR analysis revealed the removal of hemicellulose and lignin in alkalized WFs and uniform epoxy curing. Addition of fibers reduced PLA's thermal stability while acting as nucleating agents. Additionally, fibers augmented the storage modulus of biocomposites, with alkalized fibers exhibiting the highest tensile modulus in IM. FDM samples with a 0° raster angle showed superior impact resistance compared to IM counterparts. Moreover, raster angle significantly influenced FDM biocomposite properties, enhancing the tensile strength and modulus of untreated WF and cellulose fibers at 0°. Although FDM did not produce alkalized WF samples, epoxy impregnation emerged as a promising method for enhancing PLA/WF composite mechanical properties in the IM process, offering valuable insights for composite material development.

Young's modulus distributions in the depth direction within injection moldings made from polystyrene have been investigated by empolying two independent techniques. Both methods show that the material close to the surface exhibits relatively high stiffness, whereas at all other depths a lower uniform stiffness exists. The depth dependency of other material characteristics, such as tan δ peaks in the dynamic mechanical thermal analysis spectra and molecular orientation, have been investigated in an attempt to correlate them with the stiffness distributions. It appears that the thermomechanical history of the different regions within the moldings, particularly the stresses acting during flow and the temperature gradients set up during cooling, are primarily responsible for the Young's modulus distributions presented here. © 1993 John Wiley & Sons, Inc.

The structure/property relationships and morphology of glass bead–reinforced syndiotactic and isotactic polypropylene composites containing 0 to 20 vol% thermoplastic elastomer (TPE) were studied. Polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene (SEBS) and the corresponding block copolymer grafted with maleic anhydride (SEBS‐g‐MA) were used as the TPEs. The Young's modulus of hybrid composites based on s‐PP showed no dependence on the type of TPE used, whereas i‐PP hybrid composites containing SEBS had a higher Young's modulus than composites containing SEBS‐g‐MA. A comparison of the data with theoretical predictions of Young's modulus and tensile yield stress gave strong evidence of two different morphologies for the hybrid composites. The increasing tensile yield stress of s‐PP hybrid composites and i‐PP hybrid composites containing SEBS‐g‐MA was attributed to an interlayer formation and in‐situ encapsulation of glass beads, which resulted in core‐shell particles with improved interfacial interactions. In contrast, SEBS in hybrid composites based on i‐PP formed a separate dispersed phase. Crystallization and scanning electron microscopy studies also provided evidence of a core‐shell morphology for hybrid composites based on s‐PP. Results of lap‐shear and peel tests confirmed strong interfacial interaction between glass and SEBS‐g‐MA and between SEBS and s‐PP as well as i‐PP. Only above a critical volume fraction did the TPE provide significant improvement of the notched Izod impact strength of hybrid composites based on s‐PP or i‐PP.

Incorporating recycled plastics into the manufacturing process is an essential way to establish a sustainable plastics economy. However, current processes are limited by the degradation of mechanical properties, high cost, and inconsistent product quality compared with their virgin counterparts. Here, we present an upcycling strategy for waste plastics where waste acrylonitrile‐butadiene‐styrene (reABS) is first grafted with maleic anhydride (MAH), then utilized to compatibilize nylon 6(PA6)/ABS and PA6/ABS/CaCO3 blends. The reABS‐g‐MAH exhibits improved Young's modulus and tensile strength, but lower strain at break and impact strength compared with reABS. As an additive, reABS‐g‐MAH effectively compatibilizes PA6/ABS and PA6/ABS/CaCO3 blends, indicated by greatly decreased PA6 domain size, homogeneous dispersion of fillers, and narrowed glass transition temperature regions between PA6 and ABS. Adding only 5 wt% reABS‐g‐MAH increases the Young's modulus, strain at break, and impact strength of PA6/ABS blends by 26%, 180%, and 110%, respectively, compared with uncompatibilized samples. Similarly, for PA6/ABS/CaCO3 blends, the strain at break and impact strength increase by 370% and 150%, respectively, while the Young's modulus and tensile strength show increases of 5% and 10%. The results show that this strategy of using polar groups to functionalize waste plastics as compatibilizers may open numerous opportunities for upcycling waste plastics.

Additive manufacturing (AM) techniques can be applied to produce carbon-fiber-reinforced polymer (CFRP) elements. Such elements can be exposed to different environmental factors, e.g., temperature, moisture, and UV radiation, related to their operational conditions. From a variety of environmental factors, the temperature is one of the most typical. Temperature strongly influences matrix material joining together CFRP components, resulting in material strength reduction. Therefore, it is important to understand processes in the composite material caused by temperature. This experimental work investigated the thermal effects on the performances of AM CFRP composites. Specimens with unidirectional (UD) alignments of the fiber reinforcement were printed using the fused deposition modeling (FDM) technique. The printed specimens were subjected to two different thermal conditions: stable continuous at 65 °C and cyclic temperature between 50 and 70 °C. Tensile testing was performed to study the mechanical strength and Young's modulus of AM UD-CFRPs. In order to investigate the morphological structure on the surface of AM specimens, an optical microscope, scanning electron microscope (SEM), and digital microscope were utilized. Untreated (intact) samples attained the highest average tensile strength value of 226.14 MPa and Young's modulus of 28.65 GPa. The ultimate tensile strength of the sample group subjected to stable heat treatment decreased to 217.99 MPa, while the thermal cycling group reduced to 204.41 MPa. The Young's modulus of the sample group subjected to stable thermal exposure was decreased to 25.39 GPa, while for the thermal cycling group, it was reduced to 20.75 GPa. The visual investigations revealed that the intact or untreated specimen group exhibited lateral damage in top failure mode (LAT), the thermally stable group underwent edge delamination in the middle (DGM) as the nominated failure mode, and the explosive breakage at gauge in the middle (XGM) failure mode occurred in the sample from the thermal cycling group. Based on morphological observations at the microscale, the delamination, fiber pull-out, and matrix cracking were the dominant damages in the 3D-printed tensile-tested specimens. The molecular chains of the polymer changed their structure into an amorphous one, and only local motions of stretching occurred when the specimens were exposed to stable heating (prolonged). In the case of thermal cycling, the strain gradients were accumulated in the matrix material, and the local stresses increased as a result of the reheating and re-cooling exposure of the polymeric composites; the molecular motion of the long-range polymer structure was reactivated several times. Micro-cracking occurred as a result of internal stresses, which led to material failure and a reduction of the mechanical properties.

Looking at the dynamically developing market of engineering materials, there is a need to create newer functional composites. Today's economic situation related to high energy prices and environmental threats force industry to conduct sustainable production. Polymer composites based on plant raw materials are increasingly appearing on global markets, which are light, have good mechanical properties and are also pro-ecological. This work involved the production of hybrid composites based on bio-based poly (ethylene terephthalate) by means of injection molding. Two types of fibers were used simultaneously as the reinforcement phase: basalt fibers and carbon fibers in the amount of 5, 7.5, and 10 wt% of each. The produced materials were subjected to a wide range of mechanical, thermal, and functional characteristics. The experimental data were compared with the theoretical results which were calculated from different micromodels. The studies showed that with the addition of the filler, the mechanical properties of the produced composites increased, but the optimal content was found for composites with 7.5/7.5 wt% addition of fibers, where the improvement was – 81%, 337%, and 25%, for tensile strength, Young's modulus, and impact strength, respectively. In the produced materials, the thermal properties of composites were also improved, where the shrinkage decreased by min. half, and linear coefficient at least 3 times. Sufficient adhesion between the fibers and the matrix was confirmed by SEM images and mechanical micromodels, which confirmed the highest efficiency of reinforcement with a total content of 15 wt% of fibers. To assess the influence of extreme conditions on the behavior of composites, hydrolytic degradation was carried out, which showed that the addition of fibers will not increase water absorption. The mechanical tests of the incubated materials lead to the conclusion that the produced materials could be successfully used in long-term applications because the properties obtained during the tensile test have deteriorated by only max. 5%. The work showed for the first time the modification of bioPET using two types of fibers introduced simultaneously. Hybridization of bioPET with basalt and carbon fibers has shown that it is possible to create very durable composites with a high Young's modulus. The work showed that different fibers are responsible for increasing other parameters – basalt fibers increase strength, while carbon fibers increase Young's modulus. The research may contribute to the popularization of bio-based polymer composites that have high strength for low weight and are a cheaper equivalent than polyamide-based composites.

A new generation of wood polymer composite with improved thermal stability

Auxetics and Other Systems of Anomalous Characteristics

Mechanical properties of polypropylene (PP)/wood fiber composites depend not only on the properties of each primary component but also on a complex interaction of several factors such as fiber loading and size, characteristics of fiber-polymer matrix interface, and the processing conditions. Both sequential and simultaneous composites are formulated in this research. First, sequential composites are made by compounding wood fibers with PP in the presence of maleated polypropylene (MPP) as a coupling agent in a twin-screw extruder. A small amount of MPP (1 wt%) present in these sequential composites can increase the tensile strength of the composites significantly. The tensile strength and Young's modulus increase with fiber content up to 50 wt% while the elongation exhibits a logarithmic decrease with increasing fiber loading. Both shear and elongational viscosities of sequential composites increase with fiber loading and show higher shear thinning and strain thinning behavior with increasing fiber loading. Secondly, simultaneous composites are produced by in-line maleation and compounding of wood fibers with PP, maleic anhydride, and initiator in the same extruder. Similar tensile properties are observed for the simultaneous composites as the sequential composites. The effects of maleic anhydride and initiators are evaluated. Compared to virgin PP, simultaneous composite shows an initial shear viscosity decrease and then increase in shear viscosity with wood fiber content. Maleation of PP cause succinic anhydride groups to be grafted onto the PP backbone, accompanied by the degradation of PP. The succinic anhydride grafting level increases with increasing initiator and maleic anhydride concentration up to a certain level. The shear viscosity of MPP is lower than that of virgin PP but higher than that of PP/initiator sample. It is also shown that the shear viscosities increase with the initial concentration of maleic anhydride and the succinic anhydride grafting level; whereas the elongational viscosity of MPP is lower than that of virgin PP and decreases with increasing succinic anhydride grafting level. The surface energy, especially polar surface energy, of MPP can be increased significantly by contacting with water at either room temperature or the boiling point of water.

The evaluation of the effectiveness of reinforcement of polymers and polymer nanocomposites(PNCs), in particular the improvement of Young's modulus, is made by performing standardized tensile tests. Structural and morphological characterizations typically are investigated using expensive techniques like transmission electron microscopy (TEM), X- ray scattering and sometimes also rheological analyses (rotational rheometry). The objective of this study is to generate faster and economically advantageous data to verify the quality of the produced PNC-compound in an on-line measurement system. Subsequently injection molded parts are processed by using the Injection Molding Compounder (PNC-IMC) “by only one plasticizing process”. In comparison to the conventional compounding process, where the compound has to be pelletized and fed into the injection molding machine for the second plasticizing process, injection molding compounding combines these two processing steps. This paper shows first results and problems with the implementation of the Rheotens equipment into the concept of the IMC. Different processing techniques and various processing conditions were compared and the occurring effects were detected both with tensile testing and extensional melt rheology. Both, the increase of the Young's modulus by using layered silicates as nanofillersis compared to the virgin polypropylene and the correlation of the level of melt strength with Rheotens measurements is shown. These results give a good overview on both the possibilities and the limitations of the material pre-tests by the use of extensional rheology in the concept of the IMC for producing PNCs. Further studies to enable a fast and efficient way of estimating the level of reinforcement in PNCs by means of Rheotens measurements will be carried out towards industrial usability. Furthermore the verification of exfoliation and intercalation of the layered silicates in the polymer matrix using small angle X- ray scattering is planned.