ASSESSING THE PROCESSABILITY OF SUGARCANE VARIETIES
The Sugar Milling Research Institute (SMRI) is developing methods to characterise the processability of sugarcane, particularly pre-release varieties from the South African Sugarcane Research Institute’s (SASRI) breeding programme. The pith/fibre ratio and colour are presently used to characterise the processability of sugarcane; however, further parameters are required to obtain a better understanding of how a particular variety would behave during processing, particularly in the front end of the factory. A number of methods have been investigated; these include the use of a stereomicroscope to identify pith and fibre, an impact test method and a percolation test method. Each method is described and test results obtained on selected varieties are given. The suitability and feasibility of each of the different methods is discussed.
PITH/FIBRE MEASUREMENT OF SUGARCANE VARIETIES USING A STEREOMICROSCOPE
Pith/fibre ratio is presently used to characterise the millability of sugarcane. The pith/fibre ratio is measured using an instrument that separates the pith from the fibre of shredded cane samples using different sized mesh screens/sieves. The instrument uses water and air for separation. This method relies on complete separation of pith and fibre which is not always achieved, and it also assumes that the densities of pith and fibre are equal. Looking at the pith and fibre in detail under a microscope will give a better indication of the distribution of fibre and pith in sugarcane. The suitability of using a stereomicroscope to measure the pith/fibre content of different cane varieties is considered, and the method and techniques used in the measurement are given. Comparisons between the new method and standard methods are shown. The advantages, disadvantages and applications of this new measuring technique are discussed.
Modelling of Mooney viscosity relaxation in natural rubber
Abstract Better assessment of natural rubber (NR) quality and processability, through the identification of new attributes, is still a major challenge. With this scope, 12 model samples of natural polyisoprene and two of synthetic polyisoprene were characterized in terms of Mooney torque relaxation, using the standardized ISO289 method (ML(1+4)100, explained later in the Section 1 ). The main purpose of this study was to identify a model that gave a better fit for the experimental decay of Mooney torque over time (ML(t)=f(t)) than the usual power law model used before (Y=at−b, [G.M. Bristow, A.G. Sears, The use of novel parameters in the assessment of natural rubber processability, NR Technol. 18 (1987); H.G. Burhin, W. Spreutels, J.M. Campbell, MV2000 Mooney viscometer: Mooney relaxation measurements on raw polymers and compounded rubber stocks, Kautsch. Gummi Kunstst. 43 (1990) 431]). The results showed that a generalized Maxwell model, and the Wu–Abbott empirical model ( Y = 1 − a Ln ( t ) − ( b t / ( c + t ) ) ) [T. Wu, J.A. Abbott, Firmness and force relaxation characteristics of tomatoes stored intact or as slices, Postharvest Biol. Technol. 24 (2002) 59–68], recently used for describing stress relaxation of tomato flesh, allowed a better description of the relaxation curve for the samples studied than the power law or stretched exponential traditionally used. Moreover, the total relaxation time (τm) given by the generalized Maxwell model showed good correlation with the total gel content of the samples studied.