Flowable sample

The formation of non-redispersible sediment in a pesticide flowable formulation is often the primary cause of product failure during inventory/sheIf storage. In order to develop and maintain a quality pesticide flowable formulation, a formulator needs evaluation techniques which will enable him to quickly determine the relative stability performance of a sample in a non-subjective manner. Accurate sample characterization and early prediction of shelf life is also highly desirable. Many methods for flowable sample evaluation, such as sediment probing, are subjective and destructive to the integrity of the sample. Often, samples have to be aged at elevated temperatures to obtain measurable differences in stability performance within reasonable time constraints. The purpose of this paper is to describe equipment and methodology which can be utilized to measure the relative... 

The following viscometer components and operating conditions are currently being used in the determination of relative viscosity versus sample depth in flowable samples ... 

Figure 4. Comparison of Three Different Flowable Samples After 10 Months at 50°C.

Figure 5. Comparison of "Profile Curves for the Same Flowable Sample After Various Ambient Temperature Storage Intervals.

The resultant material in many cases is not flowable , which means it tends to cake or agglomerate. It is then difficult to get good partide distribution which increases the tendency toward heterogeneity and means mixing of the material before sampling is critical. 

It is known (see 91 ) that acoustic cavitation occurs in low-viscous fluids (for example, in water) in a thershold pattern. In 102) the authors carried out an experimental investigations to estimate the thershold of acoustic cavitation in flowable high polymers. Figure 20 gives the results of experiments for three different samples. It can be seen that for one sample the critical (in terms of cavitation occurence) amplitude of acoustic vibrations depends upon time, i.e., in principle, it is of long-term strength... 

Given that the bulk volume associated with the particle mass is a mixture of air and solid material, the bulk density value is highly dependent on sample history prior to measurement. Calculation of the tapped density can then be achieved by tapping the bulk powder a specified number of times (to overcome cohesive forces and remove entrapped air) to determine the tapped volume of the powder. The tapped and bulk density values can be used to define the flowability and compressibility of a powder using Carr s index and the Hausner ratio. 

The Preparation of Aqueous-Based Flowables Ranging the Sample Size from Sub-Gram to Several Gallons... 

This paper will discuss the evaluation of several wet milling systems for providing precisely controlled (percent a.i., particle size, etc.) aqueous base flowables in a wide range of sample sizes. Included will be data on grind parameters (i.e., grind time vs. grind media type and charge) for the Crescent Dental Mills, as well as the. 01,... 

Most of the milling runs presented in this paper were made on the small Crescent mills, particularly on Model 6000. This was done in an effort to fully explore the utility of this equipment as a laboratory tool for preparing very small samples of pesticide flowables. In these runs, a preemergence herbicide, dimethyl 2,3,5,6-tetrachloroterephthalate, was selected to serve as a model compound. This material has a melting point of 156 C and can be readily milled to the less than five micron size range. In the studies with the Crescent mills, a flaked technical was used which had been mortar and pestled and screened to less than 60 mesh feed material. 

The effective sample size ranges for the six mills, which we considered in this study, are summarized in Table Vlll. As can be seen, these units in concert can cover essentially the entire range of sample sizes from a few milligrams of a.i. up to 50 kg. This capability should cover sample needs for most research and field development programs. The stated sample size ranges shown in Table Vlll are based on the smallest practical sample size for each unit of a 5% flowable, and the largest sample possible of a 30 or 50% flowable. 

The graphic portrayal of a typical viscosity versus sample depth evaluation performed on a 16 oz. sample jar is depicted in Figure 2. Important evaluation parameters for the resultant curve are also depicted. The total time necessary for the evaluation of this sample (approx. 90 mm deep) was four minutes. Similar data has been generated for flowable suspensions in sample containers as tall as 15 inches (i.e., 5 gallon pail). This is accomplished by using 400 mm long spindles in conjunction with an extension for the Heliopath Stand supporting rod to provide the amount of stand travel necessary to permit the spindle to probe the entire sample depth. 

The uniformity coefficient is arrived at by dividing the width of the sieve opening that passes 10% of the sample. It is determined from a screen analysis of the material. The more uniform a mass of particles is in both size and shape, the more flowable it is likely to be. 

The point score for the evaluation of flowability of dry solids is given in Table 1. In order to measure the flowability of a powder utilizing this method, each test is made and the points can be found in the table. The total number of points would place the sample into one of the seven categories in the left column of the table. Because of its simplicity and the fact that commercial devices are available to conduct these tests (this test is ASTM test designation D 6393-99), this system is widely used in the pharmaceutical industry... 

The flowability of materials according to the literature is related to the mean time for avalanching to occur. The shorter the time the more free flowing. The scatter is related to cohesiveness ° or an irregularity factor.Lower scatter values would indicate a less cohesive material and would predict more regular flow while greater scatter would be indicative of a more cohesive material and the increased likely hood of irregular flow pafferns. The example in Fig. 10 shows a lactose sample that was sieved into two fractions one above 38 pm and one below 38 pm. 

Fig. 10 Rotating drum avalanche data from a TSI Aero-Flow automated powder flowability analyzer. The first frame shows the data output for lactose, which passed through a 38-pm screen (less than 38-pm). The output data for the original lactose sample (notscreened) is shown in the middle frame. The last frame shows the flow data for the lactose sample remaining on the 38- j,m screen (greater than 38-pm). (From Ref l)...

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