Isothermal and non-isothermal crystallization kinetics of UHMWPE composites incorporating with GNP/MWCNT

Ultra High Molecular Weight Polyethylene (UHMWPE), a captivating material, presents incomparable physical and chemical properties due to very high molecular weight and intricate crystalline process. In this study, two kinds of nano-materials, one-dimensional multi-walled carbon nanotubes (MWCNT) and two-dimensional lamellar graphene nanoplatelets (GNP), were added to UHMWPE, investigating the isothermal and non-isothermal crystallization processes of UHMWPE/nano-materials composites. Jeziorny and Mo method are all suitable for describing the non-isothermal crystallization process. Interestingly, both MWCNT and GNP did not play the role of heterogeneous nucleating agents. The crystallization activation energy of UHMWPE/nano-materials composites is slightly enlarged, proving that the addition of these two nanomaterials is unfavorable to the crystallization process. In addition, during the non-isothermal crystallization process, the neat UHMWPE exhibits a lower crystallization rate than that of samples modified by nano-materials at initial crystallization stage, and possesses a slower crystallization rate than that of samples modified by nano-materials at end crystallization stage. This phenomenon may be attributed to the fact that the incorporated nano-materials abate the number of the physical entanglement points of UHMWPE molecular chains, which weakens the restriction on the movement of molecular chains and increases the crystallization rate at the initial stage. However, the crystallization rate of the samples incorporated with nano-materials decreases rapidly with time. Besides, the Avrami exponent is about 2 in both isothermal and non-isothermal crystallization process, which may be related to the geometry of crystal growth.

Automated summary

In this study, the effect of adding two types of nano-materials (multi-walled carbon nanotubes and graphene nanoplatelets) to ultra-high molecular weight polyethylene (UHMWPE) on its isothermal and non-isothermal crystallization processes was investigated. The results revealed that the nano-materials did not act as heterogeneous nucleating agents and their addition was unfavorable to the crystallization process. The samples modified by nano-materials had a lower crystallization rate than the neat UHMWPE at the initial crystallization stage, but a faster crystallization rate at the end crystallization stage. This phenomenon may be attributed to the reduction of physical entanglement points of UHMWPE molecular chains by the incorporated nano-materials, which weakened the restriction on molecular chain movement and increased the crystallization rate at the initial stage. However, the crystallization rate of the samples incorporated with nano-materials decreased rapidly with time.