Cellulose nanofibrils (CNF) are mixed with plasticizers; sorbitol and glycerol, through high-pressure homogenization to prepare multifunctional biohybrid films. The resulting plasticized films obtained after solvent evaporation are strong, flexible and demonstrate superior toughness and optical transparency. The oxygen barrier properties of the biohybrid films outperform commercial packaging materials. The sorbitol-plasticized CNF films possess excellent oxygen barrier properties, 0.34 cm3·μm/m2·day·kPa at 50 % relative humidity, while significantly enhancing the toughness and fracture strength of the films. CNF films plasticized by 20 wt.% of sorbitol and glycerol could before rupture, be strained to about 9 % and 12 %, respectively. The toughness of the plasticized films increased by ca. 300 % compared to the pristine CNF film. Furthermore, the water vapor barrier properties of the biohybrid films were also preserved by the addition of sorbitol. CNF films plasticized with sorbitol was demonstrated to simultaneously enhance fracture toughness, work of fracture, softening behavior while preserving gas barrier properties. Highly favorable thermomechanical characteristics were found with CNF/sorbitol combinations and motivate further work on this material system, for instance as a thermoformable matrix in biocomposite materials. The unique combination of excellent oxygen barrier behavior, formability and optical transparency suggest the potential of these CNF-based films as an alternative in flexible packaging of oxygen sensitive devices like thin-film transistors or organic light-emitting diode displays, gas storage applications and as barrier coatings/laminations in packaging applications, including free-standing films as aluminium-replacement in liquid board and primary packaging, as replacement for polyethylene (PE) in wrapping paper, e. g. sweats and confectionary.

A custom-made prosthetic product is unique for each patient. Fossil-based thermoplastics are the dominant raw materials in both prosthetic and industrial applications; there is a general demand for reducing their use and replacing them with renewable, biobased materials. A transtibial prosthesis sets strict demands on mechanical strength, durability, reliability, etc., which depend on the biocomposite used and also the additive manufacturing (AM) process. The aim of this project was to develop systematic solutions for prosthetic products and services by combining biocomposites using forestry-based derivatives with AM techniques. Composite materials made of polypropylene (PP) reinforced with microfibrillated cellulose (MFC) were developed. The MFC contents (20, 30 and 40 wt%) were uniformly dispersed in the polymer PP matrix, and the MFC addition significantly enhanced the mechanical performance of the materials. With 30 wt% MFC, the tensile strength and Young´s modulus was about twice that of the PP when injection molding was performed. The composite material was successfully applied with an AM process, i.e., fused deposition modeling (FDM), and a transtibial prosthesis was created based on the end-user’s data. A clinical trial of the prosthesis was conducted with successful outcomes in terms of wearing experience, appearance (color), and acceptance towards the materials and the technique. Given the layer-by-layer nature of AM processes, structural and process optimizations are needed to maximize the reinforcement effects of MFC to eliminate variations in the binding area between adjacent layers and to improve the adhesion between layers. © 2020 by the authors.

Additive manufacturing (3D printing) enables the designing and producing of complex geometries in a layer-by-layer approach. The layered structure leads to anisotropic behaviour in the material. To accommodate anisotropic behaviour, geometrical optimization is needed so that the 3D printed object meets the pre-set strength and quality requirements. In this article a material description for polymer powder bed fused also or selective laser sintered (SLS) PA12 (Nylon-12), which is a common 3D printing plastic, was investigated, using the Finite Element Method (FEM). The Material Model parameters were obtained by matching them to the test results of multipurpose test specimens (dumb-bells or dog bones) and the model was then used to simulate/predict the mechanical performance of the SLS printed lower-leg prosthesis components, pylon and support. For verification purposes, two FEM designs for a support were SLS printed together with additional test specimens in order to validate the used Material Model. The SLS printed prosthesis pieces were tested according to ISO 10328 Standard. The FEM simulations, together with the Material Model, was found to give good estimations for the location of a failure and its load. It was also noted that there were significant variations among individual SLS printed test specimens, which impacted on the material parameters and the FEM simulations. Hence, to enable reliable FEM simulations for the designing of 3D printed products, better control of the SLS process with regards to porosity, pore morphology and pore distribution is needed.

Cellulose nanofibrils (CNF) can be produced in the form of thin, transparent andflexible films. However, the permeability of such materials to oxygen and water vaporis very sensitive to moisture, which limits their potential for a variety of packaging andencapsulation applications. Diffusion barrier coatings were thus developed to reducethe access of water molecules to enzymatically pre-treated and carboxymethylated CNFsubstrates. The coatings were based on UV curable organic-inorganic hybrids withepoxy, tetraethylorthosilicate (TEOS) and 3-glycidoxypropyltrimethylenesilane (GPTS)precursors and additional vapor formed SiNx layers. A total of 14 monolayer andmultilayer coatings with various thickness and hybrid composition were produced andanalyzed. The water vapor transmission rate (WVTR) of the bilayer epoxy/CNF film wastwo times lower compared to that of uncoated CNF film. This was partly due to the watervapor permeability of the epoxy, a factor of two times lower than CNF. The epoxy coatingimproved the transparency of CNF, however it did not properly wet to the CNF surfacesand the interfacial adhesion was low. In contrast hybrid epoxy-silica coatings led to highadhesion levels owing to the formation of covalent interactions through condensationreactions with the OH-terminated CNF surface. The barrier and optical performance ofhybrid coated CNF substrates was similar to that of CNF coated with pure epoxy. Inaddition, the hybrid coatings provided an excellent planarization effect, with roughnessclose to 1 nm, one to two orders of magnitude lower than that of the CNF substrates.The WVTR and oxygen transmission rate values of the hybrid coated CNF laminateswere in the range 5–10 g/m2/day (at 38◦C and 50% RH) and 3–6 cm3/m2/day/bar (at23◦C and 70% RH), respectively, which matches food and pharmaceutical packagingrequirements. The permeability to water vapor of the hybrid coatings wasmoreover foundto decrease with increasing the TEOS/GPTS ratio up to 30 wt% and then increase athigher ratio, and to be much lower for thinner coatings due to further UV-induced silanolcondensation and faster evaporation of byproducts. The addition of a single 150 nmthickSiNx layer on the hybrid coated CNF improved its water vapor barrier performance bymore than 680 times, with WVTR below the 0.02 g/m2/day detection limit.

In this work, systematic studies were carried out on SLS (selective laser sintering) printed samples, with two different geometries, standard test samples dumb-bells (dog bones) and tubes (Ø 30 mm and 150 mm long), consisting of two different materials, viz. PA12 (polyamide) with and without the addition of carbon fibres (CFs). These samples were tested according to their respective ISO standards. The standard test samples exhibited relatively small differences with regards to printing directions when PA12 was used alone. Their tensile strengths (σm) were approx. 75%–80% of the injection-moulded sample. The addition of carbon fibres significantly enhanced the tensile strengths, namely 50% greater for the vertically printed test sample and more than 100% greater for the horizontally printed samples, compared to the respective objects consisting of PA12 alone. The strong difference in printing directions can be attributed to the orientation of the carbon fibres. Mechanical tests on the SLS printed tubes confirmed the trends that were found in the standard test samples. Porosity and pore structure inside the SLS printed tubes were studied by combining optical microscopy and X-ray microtomography with image analysis. It was found that porosity was a general phenomenon inside the SLS printed samples. Nevertheless, there were significant differences in porosity, which probably depended on the properties of the materials used, both with and without carbon fibres, thus causing significant differences in light absorption and heat conductivity. The printed samples made of PA12 alone possessed quite a high level of porosity (4.7%), of which the size of the biggest pore was hundreds of microns. The twenty biggest pores with an average size of 75*104 ÎŒ m3 accounted for 43% of the total porosity. However, the porosity of the printed samples made from PA12 + CF was only 0.68%, with the biggest pore being only tens of microns. The corresponding average pore size of the 20 biggest pores was 72*103 ÎŒ m3, which was one order of magnitude smaller than the printed samples made from PA12 alone. Pores inside the SLS printed samples were probably responsible for a spread in the mechanical properties measured, e.g. tensile strengths, tensile (Young’s) modulus, strain at break, etc. The ratios of their standard deviations to their corresponding mean values in the standard test samples could probably be used as an indicator of porosity, i.e. the bigger the ratio, the higher the porosity.

The viscosity, tensile strength- and barrier properties of enzymatically pre-treated- (NFCEnz), carboxymethylated- (NFCCarb) and carboxymethyl cellulose (CMC) modified (NFCCMC) nanofibrillated cellulose systems (NFC) that have been produced at about the same energy consumption levels in the mechanical delamination step in the manufacturing of the different NFCs are reported. It was found that NFCEnz and NFCCMC are characterized by low degrees of fibrillation. Carboxymethylated NFC displayed superior tensile strength properties, lower fiber fragment content and a higher viscosity when compared to NFCEnz and NFCCMC. Interestingly, NFCEnz displayed equal or better barrier properties compared to the highly fibrillated NFCCarb.

Phosphate functionalized nanofibrillated cellulose (NFC) was produced through an industrially attractive process, by reacting wood pulp with a phosphate containing salt, followed by mechanical delamination through microfluidization. The degrees of delamination of the phosphorylated NFCs (judged by among others AFM-imaging, rheological studies and tensile strength measurements on NFC films) were found to improve with increasing functionalization of the pulp and number of microfluidization-passes. The NFC systems were found to display similar characteristics as other well-known NFC systems. Interestingly, however, the sufficiently delaminated phosphorylated NFCs exhibited significantly lower oxygen permeability values (at RH 50%) than the published values of several well-known highly delaminated NFC systems. The potential application of the phosphorylated NFC in packaging applications can hence be envisaged.

A comparative study of the barrier properties of cast film of polypropylene carbonate (PPC) and cast film of poly(lactic acid) (PLA) has been made in this paper. Dynamic transmission measurements were conducted to obtain the barrier properties for oxygen transmission and for water vapour transmission. A special algorithm fminsearch in Matlab was used to adapt an exponential expression to the measured values. In this way the time needed to reach a 95% level of steady state was made possible to identify. The oxygen permeability was lower for PPC compared to PLA and this could be explained by a much higher positive enthalpy of solution for oxygen in PPC. The enthalpy of diffusion was close to similar for both PPC and PLA and was higher than for enthalpy of solution. The enthalpy of water vapour permeability was higher for PPC compared to PLA and this resulted in substantially higher water vapour permeability for PLA. The uptake of water vapour was also higher for PLA compared to PPC as shown by dynamic vapour sorption measurements. Differential scanning calorimetry confirmed that PPC is an amorphous polymer and that the PLA used in this study had a minimum of crystallinity which made it comparable to PPC.

Carboxymethyl cellulose (CMC) was added in various amounts (< 10% (w/w)) to a lowcharged (enzymatically pre-treated) NFC, and the suspensions were blended by either a low-shear propeller mixing- or high shear homogenization protocol. The suspensions were thereafter oven-dried, and redispersed using a high shear protocol. It was found that the mixing method has a profound effect on the apparent rheology of the never-dried systems. The addition of highly charged CMC-grades enabled, already at 1% (w/w) addition, the apparent dispersion of dried NFC. The rheological responses (viscosity and storage modulus) of the neverdried NFC-CMC systems were judged as conserved, when the rheological responses of the redispersed systems were compared with those of never-dried systems that had been produced by propeller mixing. The rheological responses of the redispersed systems were on the other hand found to be lower when compared to the rheological responses of the never-dried systems that had been produced by high shearing mixing. However, the mechanical- and barrier properties of the redispersed systems were found to be inferior to the never-dried equivalents - regardless of the mixing protocol.

A method (Ankerfors and Lindström in Method for providing nanocellulose comprising modified cellulose fibers, 2009) was employed to physically attach anionic carboxymethyl cellulose (CMC) chains onto wood pulp, upon which it was fibrillated by a microfluidizer-type homogenizer at high applied pressures and at dilute conditions [<3 % (w/w)]. It was found that the CMC-modified pulp can be fibrillated at the same consistencies as many of the commercially available NFC products. The NFC manufacturing process was also deemed to be energy efficient, as it lacked the need for mechanical pre-treatment, which is often a prerequisite for the production of many existing NFC systems. The CMC-based NFC was studied with respect to the rheological characteristics, and was also characterized using AFM-imaging. Further, The NFC was made into films, and its tensile strength was determined together with its barrier properties. In general, the rheological characteristics (viscosity and storage modulus) together with the tensile strength and oxygen barrier properties of the films were improved with increasing the number of passes through the microfluidizer. The fibrillated CMC-modified pulp was found to be as efficient as other NFC systems when employed as dry strength additive. The employment of the investigated material, which can be produced at acceptable costs and through environmentally benign and industrially relevant processes can, hence, potentially lead to significant future savings in the energy consumption levels in the paper and cardboard manufacturing processes, which have been recognized as major application areas of NFC products.