Plasticizers for Protein‐Based Materials

This study presents a practical approach to select plasticizers for proteins. It is a case study on thermoformed wheat gluten, considered here as a model protein, and it involved 30 plasticizer candidates. The approach consisted of selecting plasticisers (30 wt%) based on visual examination, rheological and molding behavior of the dough, and finally tensile data. There was no unique relationship between the torque behavior of the dough and the mechanical properties of the films. Nevertheless, the extensibility and dough analysis indicated that the most promising plasticizers were as follows: glycerol, linear glycols, ethanol amines, diols, and trimethylolpropane. Further, considering also the stiffness, it was concluded that the most efficient plasticisers were those that contained three hydroxyl groups and the linear glycols of intermediate size. Out of those, glycerol stood out as having the highest extensibility and lowest stiffness and strength. In an attempt to predict the mechanical properties of the films based on several physical data of the compounds, it was observed that there was a weak nonlinear relationship between the stiffness/strength and the size (molecular weight/molar volume), polarity and molar refractivity of the compound. The stiffness/strength decreased with an increase in these physical parameters

Barrier Plastics, Processing of Wheat Gluten and A New Method to Measure Permeability

One way to extend the shelf life for foodstuff is to usemodified atmosphere packaging (MAP). It is important that MAPare gas tight or in some rare cases permselective to preservethe right gas mix. To be able to determine how the gas contentchanges it is essential to know the gas permeability of thewhole packaging with effects from seals, folds and possibleplasticisation effects from the products. In the first part of the study a new technique fordetermining oxygen and carbon dioxide permeability of flexiblepackaging was developed. The method was tested on very-lowdensity, low density and high density polyethylene pouches. Thepouch head-space and pouch volume of carbon-dioxide-filledpouches were measured as a function of time until anequilibrium pouch gas composition was established. Permeabilitywere obtained from the rates of carbondioxide loss and oxygenuptake. HSP-method permeability values were in good agreementwith those obtained from traditional flat-film permeabilitytechniques. The HSP-method was found to be a valuable tool fordetermining and quantifying changes in carbon dioxide andoxygen pouch barrier properties due, for example, to theexposure to olive oil or due to the existence of poorwelds. When use of MAP are growing the demands for suitable andcheap gas barrier materials are increasing. Films made fromwheat gluten, which is a by-product from the manufacture ofethanol and sweeteners, has low oxygen permeability propertiesin dry conditions and that makes it interesting as a packagingbarrier. Several studies have been performed on solution castedwheat gluten films, but to get a new material on the market itis of great importance that the material is adapted to thepresent process equipment, such as plastic extruders. Thesecond part of the study deals with a way to expand theprocessing window of wheat gluten plastisazed withglycerol. The temperature -processing window of glycerol-plasticizedwheat gluten was increased by the use of a well-known scorchretarder, salicylic acid. It was possible to extrude 30 wt.%glycerol-wheat gluten films with a die-head temperature as highas 135°C, rather than 95°C, by incorporating only 1%salicylic acid. Small effects of shear induced heating duringextrusion suggested that the acid acted as a lubricator.Chemilumiscence, in turn, showed that it also had an effect onthe heat-induced chemical changes of gluten. Tensile tests onextrudates revealed that the substantially enhanced processingtemperature was achieved to the expense of a slightly reducedductility. Tensile tests were obtained on compression-moldedsamples containing 30wt% glycerol and an additional 2.5-5% ofglycerol, salicylic acid or sulfonamide. The tensile tests,performed during the first 30 min after molding, did not revealany scorch retarding effects. However, the retarders did reducethe level of aggregation and crosslinking as compared toglycerol, observed by that fact that the fracture stress wasconsistently lower for salicylic acid and sulfonamide comparedto glycerol. The complex shearmodulus increased more slowlyabove 110-120°C with increasing salicylic acid content,indicating that it did have a scorch retarding effect

Lignin-containing coatings for packaging materials : Pilot trials

One severe weakness of most biopolymers, in terms of their use as packaging materials, is their relatively high solubility in water. The addition of kraft lignin to starch coating formulations has been shown to reduce the water solubility of starch in dry coatings. However, lignin may also migrate into aqueous solutions. For this paper, kraft lignin isolated using the LignoBoost process was used in order to examine the effect of pH level on the solubility of lignin with and without ammonium zirconium carbonate (AZC). Machine-glazed (MG) paper was coated in a pilot coating machine, with the moving substrate at high speed, and laboratory-coated samples were used as a reference when measuring defects (number of pinholes). Kraft lignin became soluble in water at lower pH levels when starch was added to the solution, due to the interactions between starch and lignin. This made it possible to lower the pH of the coating solutions, resulting in increased water stability of the dry samples; that is, the migration of lignin to the model liquids decreased when the pH of the coating solutions was reduced. No significant difference was observed in the water vapor transmission rate (WVTR) between high and low pH for the pilot-coated samples. The addition of AZC to the formulation reduced the migration of lignin from the coatings to the model liquids and led to an increase in the water contact angle, but also increased the number of pinholes in the pilot-coated samples

Plastic Composites Made from Glycerol, Citric Acid, and Forest Components

An ecofriendly approach for the synthesis of plastic biomaterials based on renewable materials suitable for 3D printing application or other applications has been developed. The material was prepared from native (microcrystalline) or amorphous cellulose, citric acid, and glycerol or ethylene glycol, by a pretreatment at 40 degrees C and a curing at 175 degrees C for 1 h. The results showed that tensile properties and the water absorption level of the material were acceptable. The highest strain at break (14%) was obtained from materials made of 10% amorphous cellulose with 90% glycerol/citric acid. It had a maximum stress at 37 MPa. Moreover, materials were without ash content. Possible applications of the material in 3D-printers were discussed. In addition, application of mechanical pulp and wood powder into novel plastic material production was discussed. Foaming during curing might be a problem for this type of material, but this can be avoided by using amorphous cellulose in the recipe

Dewatering of Softwood Kraft Pulp with Additives of Microfibrillated Cellulose and Dialcohol Cellulose

The addition of nano-and micro-fibrillated cellulose to conventional softwood Kraft pulps can enhance the product performance by increasing the strength properties and enabling the use of less raw material for a given product performance. However, dewatering is a major problem when implementing these materials to conventional paper grades because of their high water retention capacity. This study investigated how vacuum dewatering is affected by different types of additives. The hypothesis was that different types of pulp additions behave differently during a process like vacuum suction, even when the different additions have the same water retention value. One reference pulp and three additives were used in a laboratory-scaled experimental study of high vacuum suction box dewatering. The results suggested that there was a linear relationship between the water retention value and how much water that could be removed with vacuum dewatering. However, the linear relationship was dependent upon the pulp type and the additives. Additions of micro-fibrillated cellulose and dialcohol cellulose to the stock led to dewatering behaviors that suggested their addition in existing full-scale production plants can be accomplished without a major redesign of the wire or high vacuum section.DOI: 10.15376/biores.14.3.6370-6383</p

Dewatering of Softwood Kraft Pulp with Additives of Microfibrillated Cellulose and Dialcohol Cellulose

The addition of nano-and micro-fibrillated cellulose to conventional softwood Kraft pulps can enhance the product performance by increasing the strength properties and enabling the use of less raw material for a given product performance. However, dewatering is a major problem when implementing these materials to conventional paper grades because of their high water retention capacity. This study investigated how vacuum dewatering is affected by different types of additives. The hypothesis was that different types of pulp additions behave differently during a process like vacuum suction, even when the different additions have the same water retention value. One reference pulp and three additives were used in a laboratory-scaled experimental study of high vacuum suction box dewatering. The results suggested that there was a linear relationship between the water retention value and how much water that could be removed with vacuum dewatering. However, the linear relationship was dependent upon the pulp type and the additives. Additions of micro-fibrillated cellulose and dialcohol cellulose to the stock led to dewatering behaviors that suggested their addition in existing full-scale production plants can be accomplished without a major redesign of the wire or high vacuum section.DOI: 10.15376/biores.14.3.6370-6383</p

Numerical model of water removal and air penetration during vacuum dewatering

Dewatering and air flow in high vacuum suction boxes was examined. The work was mainly numerical and was based on, and compared with, previously published experimental results of vacuum dewatering from laboratory equipment and from a pilot paper machine. A previously published numerical model for wet pressing is used as the basis for this work. The aims of this study were to find new fitting parameters that allows the previous model to be used for vacuum dewatering instead of pressing, and to examine two extensions to the original model. The results indicate that the new vacuum dewatering model for moisture can predict the dewatering behavior for several different experimental data series both from laboratory equipment and a pilot paper machine using the same set of fitting parameters. Two different numerical models for air flow through the paper sheet, during vacuum dewatering, were developed based on postulating that the decrease in moisture permeability is accompanied by a simultaneous increase in air permeability. The models for air flow can also be fitted to experimental data and predict the magnitudes of air flow during vacuum dewatering. The data sets for air flow exhibit a certain degree of operator dependence though, so that one set of fitting parameters is not enough for obtaining good agreement with all data sets.Artikeln ingick som manuskript i Sjöstrands doktorsavhandling (2020): Vacuum Dewatering of Cellulosic Materials: New insights into transport phenomena in the papermaking process</p

Structural, microrheological and kinetic properties of a ternary silica-Pluronic F127-starch thermosensitive system

Hypothesis: The sol-gel transition in aqueous suspensions consisting of silica particles and thermosensitive polymer is controlled by inter-particle forces and solution properties of the polymer. Addition of a second non-thermosensitive polymer may affect the transition. The purpose of this work was to characterize the kinetics of the sol-gel transition and to understand the effects of a second non-thermosensitive polymer on the microstructure, using a combination of classical rheology and microrheology. Experiments: Classical rotational rheology as well as two microrheology methods, Multiple Particle Tracking (MPT) and Diffusing Wave Spectroscopy (DWS), were used to investigate the sol-gel transition of a ternary silica-Pluronic F127-starch thermosensitive system. Findings: Classical rheometry and DWS indicated sol-gel transition temperature similar to 25 degrees C at 1 wt% Pluronic, independently of the concentration of the other components. DWS showed a fast gelation process, less than two minutes for all samples, beside a second slow kinetic process. In the gel state, MPT indicated micro-structural and micro-viscoelastic differences compared to rotational rheology. This was explained by formation of an elastic matrix of silica and polymers in combination with assembly of silica particles in large macroporous agglomerates. Presence of starch led to breakdown of the macro porous network, leaving the homogeneous elastic network left