Study On Structure And Properties Of In-situ HDPE/POM Composites

In recent years, high density polyethylene(HDPPE) has become the research focus because of the demand for high-performance polyolefin material is on rise year by year. Meanwhile, study of modification of polyformaldehyde(POM) which is used as the commonly used engineering materials is being paid more and more attention. This study aims to achieve a new type of high-performed engineering material by synthesizing the advantages of high density polyethylene(HDPE) and polyformaldehyde(POM). So, in this study, rheology matching of different raw materials was firstly studied the blending material。 And then the best of POM and HDPE was shaped through injection molding. On the basis of the study, extrusion molding by a self-designed convergent forming die, after which structural performance of HDPE/POM blends and HDPE/POM/MPEG blends was further studied.In the dynamic rheological experiment, the rheological properties of HDPE and POM were investigated by Rotational Rheometer. The results show that:(1) the magnitude of the storage modulus and loss modulus of HDEP are inversely related to its relative molecular mass and flowability(MFR);(2) according to the fitting results of the polymer blends, the in-situ reinforcement effect is related to the flowability, when the D-value of MFR is 7~9, the in-situ reinforcement effect would be best. So, 5000 S of HDPE and M90 of POM would be the best choice for the blend system.After injection molding and extrusion molding of HDPE/POM blends, the results of structural properties show that:(1) tensile property of injection molding formed samples improved with the addition of POM. Compared with HDPE, tensile strength of HDPE/POM(80/20) blends was improved by 21.7%. Melting temperature of HDPE/POM(80/20) blends shiftted to higher temperature shown in the DSC curve and its degree of crystallinity could be up to 61.65% which improved by 19.4% compraed to HDPE. Reinforced particle and fiber structure formed by POM in the matrix could be observed in the SEM morphorgies. In the XRD parttern, FWHM of diffraction peaks became narrow with the addition of POM, which means that POM could promote the crystallization of HDPE;(2) tensile strength of extrusion molding formed HDPE was up to 33.50 MPa and improved by 67.75% compared with injection molding. And tensile strength of extrusion molding formed HDPE/POM(80/20) blends improved by 37.1% compraed with extrusion molding formed HDPE. DSC results show that extrusion molding formed blends possessed higher degree of crystallinity. For instance, the degree of crystallinity of extrusion molding formed HDPE/POM(80/20) blends was up to 62.22% and the XRD results showed that extrusion molding made the orientation of POM more consistent and could get finer grain.In order to improve the compatibility of HDPE/POM(80/20) blends, methoxypolyethylene(MPEG) was added to the system. The results showed that:(1) compatibility of blends increased with addition of compatibility and tensile strength and impact property of HDPE/POM/MPEG(80/20/0.7) increased by 6.9% and 17.8%, respectively. And furthermore, the melting temperature of HDPE/POM/MPEG(80/20/0.7) shiftted to high temperature by 2.84℃ and the degree of crystallinity increased by 7.2%. SEM and XRD results showed more uniformity of POM in matrix and more finer microcrystallite of the blends with the trace addition of MPEG;(2) During the extrusion molding of ternary blending system by using of self-designed die, it was found that: tensile strength of HDPE/POM/MPEG(80/20/0.7) blends was up to 39.89 MPa, which improved by 52.44% compared with injection molding. The results of DSC showed that the melting peak of HDPE in HDPE/POM/MPEG(80/20/0.7) blends made by extrusion molding shifted to higher temperature by 2.64℃ compared to injection molding. The calculation of(101) lattice plane in XRD pattern showed finer grain in the material.In conclusion, moderate addition of POM could enhance the properties of HDPE and small addition of MPEG could improve the compatibility of HDPE/POM blends. Along with the extrusion molding, good in-situ reinforcement blends could be made.