Micro ultrasonic powder molding for semi-crystalline polymers

Abstract

The present paper introduces micro ultrasonic powder molding (micro-UPM), a novel method for forming micro semi-crystalline polymer parts. In the proposed method, semi-crystalline polymer powder is rapidly heated and plasticized by ultrasonic vibration, after which the microcavity is filled with the melt under sonotrode pressure (PU) to form a variety of micro polymer parts. Differential scanning calorimetry, scanning electron microscopy, and nanoindentation tests demonstrate that micro-UPM UHMWPE (ultra-high molecular weight polyethylene) parts consists of nascent and melt-recrystallized phases and that energy concentrated at particle interfaces as a result of high-frequency friction, compressive deformation, and ultrasonic radiation leads to rapid diffusion and interpenetration of the chain segment. The particle interface melts result in strong co-crystallization during cooling. To investigate the effect of ultrasonic duration time (TU) on the quality of micro-UPM UHMWPE parts, different TU values are utilized to form UHMWPE parts at a PU of 16 MPa and a holding time of 5.0 s. As TU increases, the number and sizes of interparticle voids gradually decrease. A rise in the melting peak of the melt-recrystallized phase and a drop in the melting peak of the nascent phrase as well as crystallinity are further observed. When TU is only 1.5 s, the crystallinity of the micro plastic part reaches a minimum value of 54.3% and the melt-recrystallized phase fraction reaches a maximum value of 98.3%. Powder particle interfaces almost disappear in this case, and optimum quality of the micro-UPM UHMWPE part is achieved.

Influence of laser power on tensile properties and material characteristics of laser-sintered UHMWPE

“…UHMWPE is widely used in medical, industrial, military and consumer applications [11]. Due to its high molecular weight which induces a very high melt viscosity, UHMWPE parts cannot be produced easily by many conventional methods, such as extrusion and injection moulding, [12,13]. UHMWPE is processed by ram extrusion and compression moulding [14] with a reported density of 0.936 g/cm 3 , ultimate strength of 33.5 MPa and elongation of 380.4% [15].…”

Nascent particle sizes and degrees of entanglement are responsible for the significant differences in impact strength of ultrahigh molecular weight polyethylene

“…The molecular chains at the interface would move and entwine through one another. From the rheological tests, the degree of entanglement of SLL‐5 was greater than that of GUR 4150, resulting in a higher degree of interpenetration/infusion of the former's molecular chains and, thus, the generation of more severe interfacial defects between its thin layers . In addition, SEM micrographs revealed a higher number of large voids and pores in the nascent powders of SLL‐5.…”

Ultrasonic Molding Technology: Recent Advances and Potential Applications in the Medical Industry

“…The research works of Fairbanks [10], Paul and Crawford [11], Matsuoka [12], Kellomäki and Törmälä [9], Liang et al [13] and Zeng et al [14] were identified as ultrasonic compression molding. In all of them, the raw material is directly poured into the mold cavity, compacted by the sonotrode, and plasticized by ultrasonic energy inside the mold cavity.…”