Application of capillary rheometer

The capillary rheometer is mainly used in the research and development of polymer materials, provides scientific data for the production process of polymer materials, provides scientific basis for the development of new composite polymer materials, and guides the resolution of product quality disputes 1 Provide scientific basis for the development of new materials Generally, new materials are developed by studying new formula and proportion, or adding oxidants and additives in polymer materials Polymer high pressure capillary rheometer is used to study the ratio and flow curve data of different materials to test the performance of the formula If the performance can not meet our desired results, we can modify the material performance by adjusting the ratio, adding additives and other methods, and compare the flow curve before and after the change to determine the addition The influence of different agents or ratios on the fluidity of materials The flow curve of the same material may also be different, some viscosity changes rapidly with the shear rate, some viscosity changes gently with the shear rate The main reason may be the different molecular weight distribution of polymer materials The instruments for measuring the molecular weight distribution of polymer materials include rotational rheometer and gel chromatograph In the absence of these two instruments, a general inference can be made through the polymer high pressure capillary rheometer Generally speaking, the wider the molecular weight distribution range, the steeper the viscosity changes with the shear rate, the narrower the molecular weight distribution range, and the smoother the viscosity changes with the shear rate 2 To guide the production process, two main parameters should be paid attention to in the production and processing of polymer materials: one is temperature; the other is speed (shear rate) At a fixed shear rate, the flow curve at different temperatures can be measured Through the change curve of viscosity with temperature, the sensitivity of the material to temperature can be known The steeper the slope of the flow curve with temperature changes, the more sensitive it is to temperature On the contrary, if the flow curve changes smoothly with temperature, it means that the material is not sensitive to temperature Of course, it is easy to find out from the curve what temperature the melt flow performance is good and suitable for processing and production, which is the scientific basis for the formulation of production process The flow curve is very sensitive to the temperature of materials, such as nylon It is very important to control a suitable temperature to control the product quality But for the polymer material which is not sensitive to temperature, only changing the temperature has little effect on the quality control of the product Under the condition of constant temperature, the relationship between viscosity and shear rate can be obtained by measuring the relationship between flow curve and shear rate The material whose viscosity does not change with shear rate is Newtonian fluid; the material whose viscosity decreases with shear rate (shear thinning) is pseudoplastic fluid, and most polymer melts are shear thinning Another is shear thickening By obtaining the flow curve, the shear rate suitable for production and processing can be selected In general, the shear rate of polymer melt is changed by changing the rotation number of motor The shear rate is closely related to the production method Half of the shear rates of spinning, injection, extrusion and calendering are 104-105, 103-104, 101-102 and 10 (1 / s), respectively Therefore, special attention should be paid to the flow characteristics with different shear rates in the production range 3 Guide to solve product quality disputes When the product leaves the factory, the polymer raw material manufacturer often only provides the melt index index of the product Users use different batches of raw materials with the same melt index Under the same production and processing conditions, some batches of finished products are qualified and some batches are unqualified Users will complain about the suppliers of raw materials Manufacturers can use the rheological data provided by the polymer high pressure capillary rheometer to guide the solution of customer complaints It is not enough to develop the processing technology only according to the melt index Only through rheological data (viscosity changes with temperature; viscosity changes with shear rate) is the scientific basis for the formulation of processing technology The problem of quantity can be solved by adjusting the processing temperature and shear rate The rheological data provided by the polymer high pressure capillary rheometer is indeed abnormal (compared with qualified raw materials) It is proved that there are quality problems in this batch of products If only the viscosity value of polymer material is abnormal, it may be the reason of different fillers; if the viscosity changes too fast or too slow with the shear rate, it may be the reason of different average molecular weight and molecular weight distribution of material Combined with other analysis methods, we can find out the root of quality problems In addition, the polymer high pressure capillary rheometer can also be used to select the processing conditions of materials, optimize the processing formula, and control the quality of products The critical shear rate of polyolefin at different temperatures can be measured by polymer high pressure capillary rheometer, or the critical shear rate can be increased by adding modified polyolefin such as fluoroelastomer and lubricant, which can provide basis for improving product appearance quality, processing speed and production.