二异氰酸酯扩链共聚甲醛及其动态流变行为的研究

Study on the Chain Extension of Polyoxymethylene Copolymer with Diisocyanate and its Dynamic Rheological Behavior

采用4,4′-二苯基甲烷二异氰酸酯(MDI)对共聚甲醛(Co-POM)进行扩链改性,通过双螺杆挤出机进行反应性挤出,对挤出样品进行元素分析、熔体质量流动速率(MFR)及动态流变行为的测试,研究了MDI对共聚甲醛体系的扩链效果及动态流变行为的影响。结果表明,MDI是一种有效的扩链剂,样品的MFR随MDI用量的增加而降低:添加量为5%(质量分数,下同)时,MFR由27g/10min降至0.5g/10min;添加量为3%时,氮元素的含量从0变化为0.32%;并且改性后样品的流变曲线发生了明显变化:在低频区域,相同频率下,相角(δ)明显低于90°,复数黏度(η*)、储能模量(G′)和损耗模量(G″)均显著增大,δ-ω曲线上δ先降低,随后出现一个平台区域,零切黏度和剪切变稀出现在更低频区域,G′、G″与ω关系曲线的斜率变小。

With 4,4′-diphenylmethane diisocyanate（MDI）as chain extender,reactive extrusion of polyoxymethylene copolymer（Co-POM）was conducted by means of a twin-screw extruder.The results of chain extension were tested by elemental analysis and the melt flow rate（MFR）,and dynamic rheological behaviors were analyzed.The effects of MDI on the chain extension and dynamic rheological behaviors of Co-POM were studied.The results showed that MDI was an effective chain extender,the MFR of the sample decreased with the increases of the content of MDI,and it dropped to 0.5 g/10min from 27 g/10min with 5 wt% MDI.The nitrogen content of the sample increased from 0 to 0.32% when MDI was 3 wt%.The rheological curves of the materials after reactive extrusion were quite different：in the lower-frequency range with the same frequency,the phase angle（δ）was far below 90°,the complex viscosity（η^＊）,the storage modulus（G′）,and loss modulus（G″）enhanced greatly,a plateau appeared in the δ-ω curve after the δ decreased,The onsets of both zero shear viscosity and shear thinning shifted to lower frequency,and the slope of G′,G″-ω became smaller than the linear ones.