Studies On Process And Properties Of PE/PP Hot-Air Through Bonded Diaper Nonwovens

There were definite researches on bonding thermal analysis and stream guidance of hot-air through bonded diaper nonwovens(HTBDN) at home,and it was scarce that research bicomponent fibers' bonding thermal analysis in the view of fluid mechanics and heat transmission.Studies on penetrability and stream guidance of HTBDN as a kind of porous medium in the view of fractal geometry were also short.Firstly,for hot-air through bonding process as a special bonding method,the thesis caculated the enegy consumption of web in the air through bongding process in the view of PE/PP bicomponent fiber's thermal properties.It got the theoretical heat absorbption of per unit weight web by constructing a heating model of a single fiber,then found some main reasons why the theoretical heat absorbption is less than its actual energy consumption by contrasting it to actual energy consumption.It also simulated to computing the equivalent unit wind pressue of each eye on unit weight web in web bonding process.Then,the thesis compared the healthy indexes via analyzing the mechanical properties of bicomponent materials and hor-air pressure,heating temperature,heating time,cooling temperature in consolidating web mechanics,and reveal the main factors of impacting penetrability,stream guidance and tensile strength of HTBDN,analyzed the significance of several factors including the random ratio,cooling temperature and web areal density on affecting MD/CD strength ratio of HTBDN via designing a orthogonal test.The thesis put forword a new set of test method and evaluating index by building a ellipse equation base on taking MD direction as X axis and taking CD direction as Y axis.By comparing the ellipse area to similar circle of actual guidance figure,it found that taking the ellipse area as a evaluating index of actual guidance figure was available by taking PE/PP web which unit weight was 20g/m~2 as an example.At last,the thesis computed capillary volume of each fiber and unit weight web composite,including holes composited with fibers and air.It provided a theoretical support for researching absorption of diaper nonwovens via comparing actual water absorption to that of unit HTBDN including air holes,which was caculated by taking PP as hollow fiber.The thesis caculated fractal parameters of HTBDN as a kind of porous medium on basis of fractal geometry theory,and provide a new approach to research nonwovens.It was resulted that:firstly,four factors,including fibers' fineness,random ratio,heating time and temperature were the main elements on determining strength of HTBDN and finer fibers,smaller random ratio,longer heating time and higher temperature can lead bigger strength of HTBDN;secondly,the equivalent unit wind pressue of each eye on unit weight web in web bonding process was about 2.1Kpa under 65%fan's power rating and 160℃hot-air temperature and theoretical heat absorption was less than actual value.The main reason was that the convection heat transfer style of the web porous medium owned non-continuous phase,ignoring the PE(polyethylene)'s melting hidden heat and higher holes' ratio was extremely complex,there was no enough theoretical bases.The determining factors on penetrability and stream guidance of HTBDN diaper were fibers' fineness and ranking state of fibers.The web,which was synthesized from upper layer made of finer fibers and sublayer made of thick fibers,possessed the best stream guidance.Finally,net soakage of unit weight web had the close relationship with its holes' fractal parameter and the reason why its theoretical value less than the actual value was that its holes' structure and amount was difficult to measure.