第4章纤维形态的表征分解.ppt

* * * * * * * Maturity (of Cotton Fibres) Structure and growth of cotton fibres - in brief Longitudinal View Cross-sectional View “Convolution” Maturity (of Cotton Fibres) Structure and growth of cotton fibres - in brief Cotton fibres begin (after the flower dies) as thin-walled hollow cylinders They first lengthen without changing in diameter; takes around 20 days They then mature; takes about another 30 days In maturation, cellulose is deposited on the inside of the cylinder – the ‘secondary wall’ The hole down the centre (the ‘lumen’) becomes progressively smaller The outer diameter of the fibre remains virtually unchanged Maturity (of Cotton Fibres) Structure and growth of cotton fibres - in brief A Cotton fibre grows first in length … … then in wall-thickness Maturity … is related to the cell wall thickness in comparison to the lumen diameter lumen Seed surface Emerging fibre Maturity (of Cotton Fibres) Degree of thickening (?) A Ao ? = A/Ao Lumen A = area occupied by cellulose Cellulose Idealised cross-section of a cotton fibre Ao = total area (including lumen) The fibres collapse when they dry out on harvesting to give a “kidney-bean” shape Maturity (of Cotton Fibres) Cross-sectional area changes, but perimeter remains approximately constant On the plant P P Dry Technological importance Maturity largely determines whether a batch of cotton can be spun into a good yarn - or indeed into any yarn Mature/Over-mature Immature “Dead” Some maturity Variations Cause “neps” – clumps of matted fibres Maturity (of Cotton Fibres) The fibre perimeter is related to both fineness and maturity, and is involved in airflow methods for measuring these properties Maturity (of Cotton Fibres) P1 P2P1 Air flow restricted through fine fibres because large specific surface Air flows more easily through coarse fibres because smaller specific surface 成熟度测量——氢氧化钠法 18%NaOH 基于纤维形态评判 方法一——成熟度比 正常纤维、死纤维、薄壁纤维 成熟度比 M=(N-D)/200+0.7 N正常纤维百分率，D死纤维百分率 方法二——成熟纤维百分率 成熟纤维、不成熟纤维 成熟纤维百分率：