Abstract: Lac resin may possess glass transition temperature ( 7,). The T, and its theory will explainthe instability of lac resin and direct the storage temperature when it is confirmed. Under the polymerglass transition theory, we used X-ray Difraction(XRD), Dierential Scanning Calorimetry ( DSC )and Dynamic Themomechanical Analysis (DMA) to verify lac-resin's 7. According to the XRD graphand its degree of crystallinity of 2. 93% , we confirmed that lac resin is amorphous polymer. The averagespecific heat capacity difference of the five DSC measurements was 0.071 J/(g ·K). The DMA meas.urement showed the inflection point of storage modulus was 36.0 C, the peak value of loss modulus and loss factor were 27.3 ℃ and 36.0℃ respectively. Combining the XRD, DSC and DMA results, wecould confirm that lac resin possess the glass transiton and T,. The T, was 27. 3 ℃ under the DSC measurement and was 36.0 9C under the DMA measurement. The interpretation of the instability of lac resinwith the glass transiton and 7, was: when the storage temperature is below 7,, lac resin could be storedfor a long time even if the physical aging may affect the lac-resin's property; when the storage temperatureis above 7' , the storage time will be shortened because the reactive end-grups could motion which couldcause a chemical reaction. Therefore the storage temperature of lac resin should be below its 7.

Key words: differential scanning calorimetry( DSC), lac resin, glass transition temperature ( 7) ;Dynamic Thermomechanical Analysis(DMA)