Redispersible polymer powder functionalized with NMA and its adhesive properties in dry-mixed coatings

One type of redispersible polymer powder functionalized with N-hydroxymethyl acrylamide (NMA) was developed in this work. The addition of NMA proved to have great influence on the properties of the original emulsion as well as the corresponding powders. The particle size and viscosity of original emulsions both increased with the increasing of NMA amount while the colloidal stability decreased due to the generation of oligomers. However, the fluidity and adhesive performance of the resultant powders were improved obviously by adding more amounts of NMA in polymerization. Taking the above factors into consideration, we found that 3.0?wt.% of total monomers was an acceptable percentage for the NMA to be used. Poly (vinyl alcohol) (PVA) was used as protective colloids in spray drying to prevent the coalescence of emulsion particles so that the reversible dispersion of powders could be realized. The morphology of powder particles was proved to turn into ‘donut’ shape with the increasing of PVA amount, and their reconstitution ability became better. Compared with original emulsion, the reconstituted emulsion had poorer stability and dispersity due to the coalescence of polymer particles in spray drying.     

Controlling lignin particle size for polymer blend applications

Softwood lignin produced by the LignoForce System^TM was physically processed using different milling approaches to ascertain effective and scalable means to yield micro to submicron particles of controllable and uniform size. Our work suggests that wet ball‐milling using a small milling medium is the most reliable method in terms of processing efficiency and particle‐size controllability. Controllable particle size reduction would permit lignin to be used as an effective filler in polymer blends. We show that wet‐milled lignin could, subsequently, be oven‐ or spray‐dried, and, subsequently, blended with, for instance, polypropylene (PP) through co‐extrusion. The spray‐drying method produced spherical lignin aggregates smaller and more uniform than oven‐dried ones. As a consequence, spray‐dried lignin demonstrated a more uniform distribution within the polymer melt, leading to noticeable improvement in the strain—or flexibility—of the lignin‐PP polymer blends. Furthermore, it is confirmed that the investigated drying methods had no effect on the thermal stability of the resulting lignin‐PP blends. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44669.     

The Mechanism of Adhesion of Phenol-Formaldehyde Resins to Cellulosic and Lignocellulosic Substrates

The mechanism of adhesion of phenolic resins to cellulosic and lignocellulosic fibers has been explored using a nonpolymerizable bromine-labelled benzyl alcohol as a model for the adhesive. Bromine analysis by neutron activation techniques is sufficiently sensitive to show that reaction occurs much more extensively with the lignified fibers. This is attributed to the formation of covalent linkages between the model adhesive and the guaiacyl units in the lignin. The excellent general performance of phenolic adhesives on cellulose and lignocellulosic substrates can therefore be in part ascribed to the existence of high enthalpy covalent chemical bonds between adherend and adhesive.     

Development and characterization of a wood adhesive using bagasse lignin

Bagasse is spent fiber left after extraction of sugar. It is mainly used as a fuel to concentrate sugarcane juice. In the present work, the possibility of preparing wood adhesives from bagasse has been explored. The parameters for the preparation of a lignin phenol formaldehyde (LPF) adhesive, (lignin concentration, formaldehyde to phenol molar ratio, catalyst concentration, reaction time and reaction temperature) have been optimized. It was found that up to 50% of phenol can be substituted by bagasse lignin to give LPF wood adhesive having better bonding strength in comparison to a control phenol formaldehyde (CPF) wood adhesive. Prepared resins were characterized using IR, DSC and TGA. IR spectra of LPF resin showed structural similarity with CPF resin. Thermal stability of LPF resin was found to be lower as compared to CPF resin. DSC studies reveal a lower curing temperature for LPF adhesive in comparison to CPF adhesive. A shelf-life study reveals that LPF exhibits consistent behavior as compared to CPF in respect to adhesive strength.     

The Mechanism of Adhesion of Phenol-Formaldehyde Resins to Cellulosic and Lignocellulosic Substrates

The mechanism of adhesion of phenolic resins to cellulosic and lignocellulosic fibers has been explored using a nonpolymerizable bromine-labelled benzyl alcohol as a model for the adhesive. Bromine analysis by neutron activation techniques is sufficiently sensitive to show that reaction occurs much more extensively with the lignified fibers. This is attributed to the formation of covalent linkages between the model adhesive and the guaiacyl units in the lignin. The excellent general performance of phenolic adhesives on cellulose and lignocellulosic substrates can therefore be in part ascribed to the existence of high enthalpy covalent chemical bonds between adherend and adhesive.     

Concentration and Drying of Tea Polyphenols Extracted from Green Tea Using Molecular Distillation and Spray Drying

The purpose of this study was to develop a method of combining molecular distillation and spray drying to concentrate and dry tea polyphenols extracts. Molecular distillation and spray drying of tea phenols extracts were performed using an orthogonal array design. The order of importance that influenced molecular distillation was distillation temperature > flux > rotational speed. The optimal conditions for concentration by molecular distillation were 70°C distillation temperature, 10 mL/min flux, and 1,200 n/min rotational speed. Inlet temperature was found to be the most important determinant of spray drying. The order of importance that influenced the spray drying was inlet temperature > feed flux > wind capacity > feed concentration. The optimal conditions for drying of tea polyphenols extracts by spray drying were determined as follows: 170°C distillation temperature, 3 mL/min feed flux, 30% feed concentration, and 30 m³/h wind capacity. Results of this study indicated that the combination of molecular distillation and spray drying was very suitable for the concentration and drying of tea polyphenols extracts. Using this approach to process tea polyphenol extracts can not only maintain the quality of tea polyphenols but also save time and energy.     

Spray Drying of Biopharmaceuticals: Stability and Process Considerations

Spray drying represents an elegant one-step process for producing biopharmaceutical formulations with unique particle characteristics. However, the full potential of spray drying of therapeutic/proteins/peptides has yet to be fully exploited. The reluctance of utilizing spray drying for formulation development may stem from the fact that the process oftentimes subjects the therapeutic actives to temperatures in excess of 100°C, which is a concern for thermally labile drugs as spray drying was performed primarily on co-current spray dryer in a single-stage mode. In this review we discuss the respective dehydration mechanisms of spray drying and the appropriate formulation strategies that can be taken to minimize detrimental effects on biomolecules.     

Spray Drying of Biopharmaceuticals: Stability and Process Considerations

Spray drying represents an elegant one-step process for producing biopharmaceutical formulations with unique particle characteristics. However, the full potential of spray drying of therapeutic/proteins/peptides has yet to be fully exploited. The reluctance of utilizing spray drying for formulation development may stem from the fact that the process oftentimes subjects the therapeutic actives to temperatures in excess of 100°C, which is a concern for thermally labile drugs as spray drying was performed primarily on co-current spray dryer in a single-stage mode. In this review we discuss the respective dehydration mechanisms of spray drying and the appropriate formulation strategies that can be taken to minimize detrimental effects on biomolecules.     

Adhesive Properties of Cured Phenylethynyl-Terminated Imide Oligomers

As part of a program to develop structural adhesives for high performance aerospace applications, phenylethynyl-terminated imide oligomers are under evaluation. Imide oligomers with different molecular weights and compositions endcapped with either 4-(3-aminophenoxy)-4'-phenylethynylbenzophenone (3-APEB) or 4-phenylethynylphthalic anhydride (PEPA) have been prepared and characterized. These oligomers exhibit excellent processability. After heating to 350°C for 1 hour, the terminal phenylethynyl groups have reacted to provide chain extension, branching and crosslinking. The cured polymers exhibit excellent solvent resistance and high mechanical properties as neat resins and in various adhesive forms (tensile shear, sandwich flatwise tension and climbing drum peel specimens). The chemistry and properties of these phenylethynyl-terminated imide oligomers are discussed.     

Development and characterization of a lignin–phenol–formaldehyde wood adhesive using coffee bean shell

In the present study, the possibility of development of a wood adhesive using coffee bean shell lignin (Cbsl) has been explored. Cbsl-modified phenolic adhesive has been prepared by replacing phenol with lignin at different weight percents. The optimization of weight percent lignin incorporation was carried out with respect to mechanical properties. It was found that up to 50 wt% of phenol could be replaced by Cbsl to give lignin–phenol–formaldehyde adhesive (LPF) with improved bond strength in comparison to control phenol–formaldehyde (CPF). Optimized LPF and CPF adhesives were characterized by IR, DSC and TGA. The IR spectrum of LPF showed structural similarity to CPF. Thermal stability of LPF adhesive was found to be lower as compared to that of CPF. DSC studies revealed a higher rate of curing in the LPF adhesive.     

Supercritical CO2 Spray Drying of Ethyl Cellulose (EC) for Preparing Microparticles

Even though common spray drying has been widely used for drying food and related products, the effect of drying conditions of supercritical CO₂ spray drying on the particle sizes of dried products has not been well studied. The objective of this study was to study the effect of drying conditions and design parameters on the particle sizes of biomaterials dried with supercritical CO₂ spray drying. The ethyl cellulose (EC) microparticles were prepared with supercritical CO₂ as the dry medium using an experimental spray-drying apparatus. This research studied the influences of spray nozzle diameter, mass ratio of gas to liquid, solution concentration, temperature, and pressure on the physical characteristics of ethyl cellulose microparticles. The results indicated that the average size of the dried particles ranged from 1.07 to 9.84 µm. The spray nozzle with 8-mm diameter produced smaller microparticles with narrower distribution than the 4-mm spray nozzle. The average particle size increased with the increase of the ratio of gas to liquid. Also, the average size and distribution of the microparticles increased with the rise of temperature and solution concentration but decreased with the increase of pressure.     

Preparation and Characterization of Demethylated Lignin-Polyethylenimine Adhesives

Petrochemical-based adhesives such as urea-formaldehyde and phenol-formaldehyde resins are predominant wood adhesives. In this study, a new wood adhesive from lignin was developed and characterized. The new adhesive consisted of demethylated kraft lignin (DKL), a byproduct in the production of dimethyl sulfoxide from kraft lignin, and a polyethylenimine (PEI). Lap-shear specimens bonded with this new DKL-PEI adhesive system had very high shear strength and were very water-resistant. The effects of the preparation time, the curing conditions, the total solids content of the adhesive, the DKL/PEI weight ratio and the molecular weight of PEI on the shear strength and water-resistance of the resulting lap-shear specimens were studied in detail. Investigation on the curing chemistry of this new adhesive revealed that phenolic hydroxyl groups were oxidized to form quinones that further reacted with PEI. It was proposed that the curing mechanisms of this DKL-PEI adhesive were similar to the quinone-tanning processes in nature.     

Preparation and Characterization of Demethylated Lignin-Polyethylenimine Adhesives

Petrochemical-based adhesives such as urea-formaldehyde and phenol-formaldehyde resins are predominant wood adhesives. In this study, a new wood adhesive from lignin was developed and characterized. The new adhesive consisted of demethylated kraft lignin (DKL), a byproduct in the production of dimethyl sulfoxide from kraft lignin, and a polyethylenimine (PEI). Lap-shear specimens bonded with this new DKL-PEI adhesive system had very high shear strength and were very water-resistant. The effects of the preparation time, the curing conditions, the total solids content of the adhesive, the DKL/PEI weight ratio and the molecular weight of PEI on the shear strength and water-resistance of the resulting lap-shear specimens were studied in detail. Investigation on the curing chemistry of this new adhesive revealed that phenolic hydroxyl groups were oxidized to form quinones that further reacted with PEI. It was proposed that the curing mechanisms of this DKL-PEI adhesive were similar to the quinone-tanning processes in nature.     

Epoxy-lignin polyblends: effects of various components on adhesive properties

Polyblends based on different epoxy pre-polymers, various lignins, and some additives such as fillers or a third polymer were prepared at room temperature and thermally cured. The effects of the different components, such as epoxy pre-polymer, hardener, lignin type, lignin molecular weight, filler, and a third polymer, on the adhesive properties of the polyblends were studied. The adhesive properties of the epoxy-lignin (EP-L) polyblends as determined by shear strength testing (by tension loading) correlated well with the type of lignin (i.e. hardwood or softwood) and lignin molecular weight. A variety of epoxy-hardener systems with lignin (up to 20%, in some cases) resulted in an improvement in their adhesive joint shear strength. The improvements varied from 112% to 178% of the control epoxy for different epoxy-hardener systems. The adhesive joint shear strength of EP-L was not much affected by the addition of 20% by weight of mineral fillers. The presence of a third polymeric component such as poly(vinyl chloride) (PVC) or phenoxy resin had a beneficial effect on the adhesive properties of the EP-L polyblends. This work demonstrates that a wide variety of commercial lignins, epoxy pre-polymers, hardeners, mineral fillers, and third polymeric components can be employed in EP-L polyblends with an improvement in the adhesive properties and a cost advantage.     

Some Aspects of Bond Formation and Failure in Adhesive Wood Joints

An investigation has been made of the effect of varying glue-spread on the bond strength of holly (Ilex aquifolium) using three adhesives and three different wood sections. The glue-spreads are lower than those normally used, and it has been found with edge-grain joints that 100% cohesive wood failure can occur with a glue-spread as low as 2.7mg/cm². Scanning electron microscopy shows that interlocking between adhesive and adherend does not occur. Factors leading to delamination and joint failure are discussed.

Lignin, without further addition, has been shown to be a useful wood adhesive. It has also been shown that it is possible to make end-grain joints without the use of an adhesive; the lignin present in the wood specimens is considered to be responsible for such joints.     

Star oligomers for low VOC polyurethane coatings

Conclusion  Hydroxyl functional star oligomers prepared by ring-opening polycondensation have a narrow molecular weight and composition distribution. Such oligomers give a solids/viscosity advantage over linear structures at the same molecular weight and can be used in low VOC two component polyurethane coatings. The solids/viscosity advantage is a combination of the highly branched structure and the narrow molecular weight distribution. Acrylic polyols formulated at the same molecular weight/polarity/average functionality and hydroxyl value give poorer drying properties. This difference can be explained by the fact that the free radical polymerisation technique leads to polymer compositions having a broad molecular weight and functionality distribution and high fractions of polymer with a low functionality. The potlife of acrylic polyols based formulations is adversely affected by the higher fractions of high molecular weight material and with a high average functionality. In low VOC polyurethane formulations star oligomers need to be formulated within a narrow range of compositions (TG, polarity), functionality and molecular weight to get an optimum balance of drying properties and potlife.     

Physical and Chemical Effects in An Epoxy Resin Exposed to Water Vapour

A commercial epoxy adhesive based on DGEBA cured with dicyandiamide (DDA) and containing fillers has been aged in water vapour (ca. 100% RH) at various elevated temperatures, Viscoelastic characterisation was effected after ageing for various times up to saturation and after subsequent drying. Young's modulus in the glassy state is reduced after water sorption but returns virtually to its original value after drying, suggesting physical weakening due to plasticisation whereas, in the rubbery state, the observed diminution is only slightly restored on drying. An analysis based on the theory of rubber elasticity leads to the conclusion that chemical degradation is occurring by hydrolysis and chain scission. Gravimetric measurements effected on the polymer exposed to vapour for a fixed time and then dried to (virtual) equilibrium show an increase in weight followed by a decrease and finally a weight loss as exposure time is increased. A theory is proposed to explain the phenomena by initial chemical combination of water followed by leaching of severed chain segments. Calculations of average inter-crosslink molecular weight using both viscoelastic and gravimetric data are in good agreement. It is concluded that long-term exposure of the epoxy adhesive to water leads to both reversible (physical) and irreversible (chemical) degradation of the material.     

Dairy Milk Particles Made with a Mono-Disperse Droplet Spray Dryer (MDDSD) Investigated for the Effect of Fat

Mono-disperse droplet generation and subsequent drying in a spray-drying chamber, i.e., mono-disperse droplet spray dryer (MDDSD), provides a better-defined “flight experience” for liquid droplets. The related particle formation can be investigated more easily than that in the usual poly-disperse droplet spray dryer (PDDSD). Previously, skim milk, which is of high protein and high lactose content and is one of the two main dairy fluids that are processed into powder form for consumer markets, was subjected to this kind of investigation in Australia. Here, whole milk, which is the other main dairy fluid, has been spray-dried in a MDDSD set-up at Xiamen University (China). Because the initial droplet size is uniform, measurable, and the particle morphology after drying is consistent, it was possible to investigate the initial solids content effect upon shrinkage and inlet air temperature effect upon shrinkage. In contrast to what had been found for skim milk particles, the formation of the fat-containing (whole milk) particles does not follow the perfect shrinkage model as the skim milk does. This work has improved our quantitative understanding of the whole milk drying process. A fundamental analysis invoked with a modified one-dimensional modeling of spray drying has been given that has shown some further insight about the process.     

SPRAY DRYING CHARACTERISTICS BY A CENTRIFUGAL PRESSURE NOZZLE WITH LARGE ORIFICE DIAMETER

A study was made of a centrifugal pressure nozzle with large orifice diameter (8-10 nun) for producing dry milk in capacity of 2-3 tons per hour to develop some performance data on spray distribution, drop size distribution, and capacity with changing spray drying conditions such as nozzle pressure, orifice diameter and spray angle.

Experimental results were shown as follows.

(1) A centrifugal pressure nozzle of large capacity such as 5,000- 5,500 l/hr at 150 kg/cm2 spray pressure and 110°s ray angle was designed by using the nozzle parameter Si/dedi√di/di.

(2) Atomization characteristics were greatly affected by the ratio of orifice diameter (de) to the length (L) of the nozzle core. The smaller the ratio, around 0.125, the better are the atomizing effects.

(3) The large orifice can be used at least 3,000 hr in the spray drying operation for milk without any wear in the orifice although it is only made of stainless steel.

As a result, a spray dryer of large capacity for dry milk has been operated by a mono nozzle with a large orifice without any trouble for a long time