A Study On The Porosity Structure And Moisture Absorption Property Of Hemp

As a kind of biological improved fiber, hemp which was claimed with lowtetrahydrocannabinol (THC) already has a good commercial development in China.Blending with cotton is a main application of hemp fiber nowadays. According to theblending processing technology of hemp and cotton, this paper did some research onthe pore structure and moisture absorption performance of crude hemp fiber and hempfiber before and after high concentration sodium hydroxide treatment and1,2,3,4-tetracarboxylic acid (BTCA) crosslinking finishing in consideration ofmercerizing and anti-wrinkle treatment to provide some theory reference.Combining with the degumming process, the influence of alkaline treatment onnon-cellulosic substances and porosity of crude hemp fiber were discussed. TheGC-MS analysis method was used to analyze the constituent and content of thecompound extracted from crude hemp fiber by chloroform. The result showed thatcrude hemp fiber still had THC after biological improvement, and THC could beremoved by common degumming processing.Further study, the residual content of surface gum and THC of crude hemp fiberdecreased as the time of alkaline treatment increasing. No THC in the chloroformextract was detected after60minutes of treatment with alkaline in experimentcondition. There were some pores whose diameters was between8.4~14nm andalmost no micropores for nitrogen sorption in crude hemp fiber. The number of poreswhose diameter was in14~47nm significantly increased and there were more poresbetween8.4~14nm and47~195.3nm in diameter after alkaline treatment which wascaused by the remove of gum.At the same time, an instrument was built by the constant temperature&humidity equipment and electronic balance which was connected to a computer to testthe moisture regain of different textiles in different relative humidity. Combining withthe moisture absorption property and the result of nitrogen absorption test, theporosity of hemp textile was discussed. The result indicated that the pore volume ofhemp was0.348mL/g which was larger than cotton’s. The pore size of hemp textile was almost in the range of16~102nm in diameter. The extent of the hysteresis clearlydecreased with the increasing relative humidity and hemp showed a more distincthysteresis than cotton which indicated that the moisture absorption and desorption hadless influence on fiber physical structure in high relative humidity and the physicalstructure of hemp was easier to be changed than cotton’s in a certain relativehumidity.Fibers swelled and the crystallinity of fiber decreased after high concentrationsodium hydroxide treatment, which resulted in a homogenization of pores’ size,increasing of micropores and sharply decreasing of pores between15.7~195.3nm indiameter. A better performance of moisture sorption and a more distinct hysteresiswere showed after high concentration sodium hydroxide treatment.1,2,3,4-tetracarboxylic acid (BTCA) crosslinking finishing made a significantdecrease of nitrogen sorption on hemp fiber. The volume of pores in15.7~102nmdecreased and the pores in8.5~15.7nm increased. The little change of moisturesorption property and a less distinct hysteresis indicated a more stable structure ofhemp after crosslinking finishing.