Jim Jones - Academia.edu (original) (raw)
Papers by Jim Jones
IEEE Transactions on Reliability, 1969
Powder Technology, 2008
Drying experiments on single droplets of aqueous amorphous polymer solution show morphological ch... more Drying experiments on single droplets of aqueous amorphous polymer solution show morphological changes towards the end of drying that result in an under-prediction of the drying rate using an effective diffusion based model. Alternately, other researchers argue that the receding interface model more accurately reflects the physics of drying by predicting a fixed droplet radius once a specified surface condition is reached, usually the saturation concentration. However, this surface condition is not adequate for many skin forming materials. The conditions at which droplet radial contraction ceases will be determined by the balance between internal moisture loss causing a collapsing pressure and the mechanical strength of the surface skin. Because measurements and prediction of surface stress are difficult, it is proposed that they are related to the state of the polymer solution at the surface which is defined by the proximity of the surface temperature to its glass transition temperature, (T −T g ). In this work, an effective diffusion model is used to predict ideal shrinkage until a critical temperature difference or (T −T g ) crit is reached where the surface of the droplet becomes fixed and the skin grows towards the droplet centre, that is, as a receding interface. For maltodextrin DE5, a (T − T g ) crit of 20°C was found to provide an accurate prediction of the drying rate. While these results show (T −T g ) crit is indicative of mechanical stress development, it points to a need for further understanding of mechanical stress development in skin forming polymers during drying.
Journal of Food Engineering, 2009
Droplet impact and spreading is an important phenomenon that contributes to the quality of the co... more Droplet impact and spreading is an important phenomenon that contributes to the quality of the coatings applied to food powders in air-suspension coating operations. This work investigates the dynamics of spreading 2.8 mm droplets containing maltodextrin DE5 at 20 wt% and 40 wt% in water, at an impact velocity of 2.6 m s À1 . The impact surface was anhydrous milkfat which was treated with three food-grade lecithin products to alter the surface hydrophobicity. Results were analysed with respect to the maximum spread diameter achieved $2 ms after impact and the final spread diameter achieved 2-4 s later. Lecithination of the surface did not affect the maximum spread diameter but resulted in greater final spread diameters. This is because lecithination reduces the equilibrium contact angle of the droplet on the surface. However, addition of lecithin to the droplet produced the same final spread diameters regardless of the surface treatment. This has the processing advantage where only the coating formulation need be manipulated to obtain the best spreading characteristics and avoid the extra processing step to modify the chemical characteristics of the substrate surface.
Journal of Food Engineering, 2007
A probe tack test was used to map the level of stickiness of droplets containing 20 and 40 wt% of... more A probe tack test was used to map the level of stickiness of droplets containing 20 and 40 wt% of maltodextrins DE5, DE10 and DE18 as they dried at 40 and 78°C. As skin formation progressed, the stickiness increased to a maximum then decreased in most cases until the droplet was no longer sticky (non-adhesive state). The results show the expected trends; lower DE maltodextrins (higher molecular weight) were sticky for only a short time over a narrow range of bulk moisture contents, and addition of glycerol and maltodextrin DE18 to maltodextrin DE5 act as plasticisers resulting in a broadening of the stickiness profiles. Glass transition temperatures were measured for each maltodextrin at a range of moisture contents. They indicate that the solutions should be sticky when, in fact, the probe tack tests show that they are non-adhesive. This indicates a difference between the surface and the bulk measured moisture content and possibly also temperature, as expected in a drying system. However, because surface moisture content and temperature can not be measured, the stickiness results were not able to be directly related to the surface glass transition temperature of the maltodextrins.
Powder Technology, 2007
A review of air-suspension particle coating concluded that, in order to speed product and process... more A review of air-suspension particle coating concluded that, in order to speed product and process development, a phenomenological approach is necessary to develop generic guidelines for the selection of coating materials and process variables. This paper identifies 10 fundamental phenomena (micro-level processes) that occur during an air-suspension particle coating process: particle motion, atomisation, droplet-particle collision, droplet impact and adherence, droplet impact and spreading, infiltration, drying, film formation, layering and inter-particle agglomeration. Their relevance to the coating objectives is discussed and from these four are identified as key micro-level processes: drying, droplet impact and spreading, and stickiness which encompasses the two key micro-level processes of droplet impact and adherence and interparticle agglomeration. It is believed that significant advances in particle coating research can be made through examination of these key microlevel processes.
Powder Technology, 2007
Air-suspension particle coating has been slow to develop in the food industry. This is not surpri... more Air-suspension particle coating has been slow to develop in the food industry. This is not surprising considering the economic constraints for low cost ingredients and low cost processing. Therefore, a need exists to adapt the process and formulation knowledge developed in the high-value pharmaceutical and health care industries to higher volume, low-cost production in the food industry. This paper reviews the current state of the art of air suspension coating as applied to the food industry. Of the few current applications, most have been developed by statistical experimentation which belies an understanding at the interface between food science and process engineering. This review concludes that a phenomenological approach is necessary in order to advance knowledge and accelerate product development. Such an approach will yield results independent of both the substrate powder and the coating device, which can be applied widely to select suitable coating materials and methods of application. A following paper will then elucidate key micro-level phenomena and discuss their implications.
International Journal of Food Engineering, 2009
Page 1. Volume 5, Issue 2 2009 Article 7 International Journal of Food Engineering Effect of Fine... more Page 1. Volume 5, Issue 2 2009 Article 7 International Journal of Food Engineering Effect of Fines on Agglomeration in Spray Dryers: An Experimental Study Anna M. Williams, Fonterra Research Centre, New Zealand Jim R. Jones, Massey University, New Zealand ...
Journal of Food Engineering, 2007
This paper develops the methodology used to track the development of stickiness for droplets of a... more This paper develops the methodology used to track the development of stickiness for droplets of amorphous skin-forming solutions during drying, by means of the probe tack test. Three material solutions were selected for study: maltodextrin DE5, whey protein isolate and gum arabic, each at two concentrations between 20 and 40 wt%. Two air temperatures were used for drying, 40 and 78°C. Three modes of failure were observed, cohesive, adhesive and cohesive-adhesive corresponding respectively to failure within the viscous bulk of the solution, at the adhesive interface, or a combination which was often associated with spot tack where partial adhesion remains at the probe surface. Stickiness was recorded as a peak tensile strength and this varied with drying. Early in drying, the peak tensile strengths were low and reproducibility was relatively good with a COV ± 3.4%. Later in drying, the peak tensile strength reached a maximum and reproducibility diminished with a COV ± 7.2%, due to both the changing failure mode associated with spot tack and uncertainty in the contact area between the probe and the sample surface. Subsequently, the surface rapidly became dry and no adhesion was observed. All three material solutions had this profile but the location of the maximum tensile strength and point of non-adhesion varied with drying temperature, initial solution concentration and material type. Importantly, all solutions reached the point of non-adhesion when the bulk moisture contents were still relatively high, $1 kg kg À1 . This means materials such as maltodextrin DE5, whey protein isolate and gum arabic offer distinct advantages in food coating systems because they are sticky over a small range of bulk moisture contents and the surfaces are easily dried below the point of non-adhesion thus minimising the probability of unwanted inter-particle agglomeration. The probe tack test is, therefore, a useful tool for formulation and drying process design.
IEEE Transactions on Reliability, 1969
Powder Technology, 2008
Drying experiments on single droplets of aqueous amorphous polymer solution show morphological ch... more Drying experiments on single droplets of aqueous amorphous polymer solution show morphological changes towards the end of drying that result in an under-prediction of the drying rate using an effective diffusion based model. Alternately, other researchers argue that the receding interface model more accurately reflects the physics of drying by predicting a fixed droplet radius once a specified surface condition is reached, usually the saturation concentration. However, this surface condition is not adequate for many skin forming materials. The conditions at which droplet radial contraction ceases will be determined by the balance between internal moisture loss causing a collapsing pressure and the mechanical strength of the surface skin. Because measurements and prediction of surface stress are difficult, it is proposed that they are related to the state of the polymer solution at the surface which is defined by the proximity of the surface temperature to its glass transition temperature, (T −T g ). In this work, an effective diffusion model is used to predict ideal shrinkage until a critical temperature difference or (T −T g ) crit is reached where the surface of the droplet becomes fixed and the skin grows towards the droplet centre, that is, as a receding interface. For maltodextrin DE5, a (T − T g ) crit of 20°C was found to provide an accurate prediction of the drying rate. While these results show (T −T g ) crit is indicative of mechanical stress development, it points to a need for further understanding of mechanical stress development in skin forming polymers during drying.
Journal of Food Engineering, 2009
Droplet impact and spreading is an important phenomenon that contributes to the quality of the co... more Droplet impact and spreading is an important phenomenon that contributes to the quality of the coatings applied to food powders in air-suspension coating operations. This work investigates the dynamics of spreading 2.8 mm droplets containing maltodextrin DE5 at 20 wt% and 40 wt% in water, at an impact velocity of 2.6 m s À1 . The impact surface was anhydrous milkfat which was treated with three food-grade lecithin products to alter the surface hydrophobicity. Results were analysed with respect to the maximum spread diameter achieved $2 ms after impact and the final spread diameter achieved 2-4 s later. Lecithination of the surface did not affect the maximum spread diameter but resulted in greater final spread diameters. This is because lecithination reduces the equilibrium contact angle of the droplet on the surface. However, addition of lecithin to the droplet produced the same final spread diameters regardless of the surface treatment. This has the processing advantage where only the coating formulation need be manipulated to obtain the best spreading characteristics and avoid the extra processing step to modify the chemical characteristics of the substrate surface.
Journal of Food Engineering, 2007
A probe tack test was used to map the level of stickiness of droplets containing 20 and 40 wt% of... more A probe tack test was used to map the level of stickiness of droplets containing 20 and 40 wt% of maltodextrins DE5, DE10 and DE18 as they dried at 40 and 78°C. As skin formation progressed, the stickiness increased to a maximum then decreased in most cases until the droplet was no longer sticky (non-adhesive state). The results show the expected trends; lower DE maltodextrins (higher molecular weight) were sticky for only a short time over a narrow range of bulk moisture contents, and addition of glycerol and maltodextrin DE18 to maltodextrin DE5 act as plasticisers resulting in a broadening of the stickiness profiles. Glass transition temperatures were measured for each maltodextrin at a range of moisture contents. They indicate that the solutions should be sticky when, in fact, the probe tack tests show that they are non-adhesive. This indicates a difference between the surface and the bulk measured moisture content and possibly also temperature, as expected in a drying system. However, because surface moisture content and temperature can not be measured, the stickiness results were not able to be directly related to the surface glass transition temperature of the maltodextrins.
Powder Technology, 2007
A review of air-suspension particle coating concluded that, in order to speed product and process... more A review of air-suspension particle coating concluded that, in order to speed product and process development, a phenomenological approach is necessary to develop generic guidelines for the selection of coating materials and process variables. This paper identifies 10 fundamental phenomena (micro-level processes) that occur during an air-suspension particle coating process: particle motion, atomisation, droplet-particle collision, droplet impact and adherence, droplet impact and spreading, infiltration, drying, film formation, layering and inter-particle agglomeration. Their relevance to the coating objectives is discussed and from these four are identified as key micro-level processes: drying, droplet impact and spreading, and stickiness which encompasses the two key micro-level processes of droplet impact and adherence and interparticle agglomeration. It is believed that significant advances in particle coating research can be made through examination of these key microlevel processes.
Powder Technology, 2007
Air-suspension particle coating has been slow to develop in the food industry. This is not surpri... more Air-suspension particle coating has been slow to develop in the food industry. This is not surprising considering the economic constraints for low cost ingredients and low cost processing. Therefore, a need exists to adapt the process and formulation knowledge developed in the high-value pharmaceutical and health care industries to higher volume, low-cost production in the food industry. This paper reviews the current state of the art of air suspension coating as applied to the food industry. Of the few current applications, most have been developed by statistical experimentation which belies an understanding at the interface between food science and process engineering. This review concludes that a phenomenological approach is necessary in order to advance knowledge and accelerate product development. Such an approach will yield results independent of both the substrate powder and the coating device, which can be applied widely to select suitable coating materials and methods of application. A following paper will then elucidate key micro-level phenomena and discuss their implications.
International Journal of Food Engineering, 2009
Page 1. Volume 5, Issue 2 2009 Article 7 International Journal of Food Engineering Effect of Fine... more Page 1. Volume 5, Issue 2 2009 Article 7 International Journal of Food Engineering Effect of Fines on Agglomeration in Spray Dryers: An Experimental Study Anna M. Williams, Fonterra Research Centre, New Zealand Jim R. Jones, Massey University, New Zealand ...
Journal of Food Engineering, 2007
This paper develops the methodology used to track the development of stickiness for droplets of a... more This paper develops the methodology used to track the development of stickiness for droplets of amorphous skin-forming solutions during drying, by means of the probe tack test. Three material solutions were selected for study: maltodextrin DE5, whey protein isolate and gum arabic, each at two concentrations between 20 and 40 wt%. Two air temperatures were used for drying, 40 and 78°C. Three modes of failure were observed, cohesive, adhesive and cohesive-adhesive corresponding respectively to failure within the viscous bulk of the solution, at the adhesive interface, or a combination which was often associated with spot tack where partial adhesion remains at the probe surface. Stickiness was recorded as a peak tensile strength and this varied with drying. Early in drying, the peak tensile strengths were low and reproducibility was relatively good with a COV ± 3.4%. Later in drying, the peak tensile strength reached a maximum and reproducibility diminished with a COV ± 7.2%, due to both the changing failure mode associated with spot tack and uncertainty in the contact area between the probe and the sample surface. Subsequently, the surface rapidly became dry and no adhesion was observed. All three material solutions had this profile but the location of the maximum tensile strength and point of non-adhesion varied with drying temperature, initial solution concentration and material type. Importantly, all solutions reached the point of non-adhesion when the bulk moisture contents were still relatively high, $1 kg kg À1 . This means materials such as maltodextrin DE5, whey protein isolate and gum arabic offer distinct advantages in food coating systems because they are sticky over a small range of bulk moisture contents and the surfaces are easily dried below the point of non-adhesion thus minimising the probability of unwanted inter-particle agglomeration. The probe tack test is, therefore, a useful tool for formulation and drying process design.