Thermal Welding by the Third Phase Between Polymers: A Review for Ultrasonic Weld Technology Developments

Abstract

Ultrasonic welding (USW) is a promising method for the welds between dissimilar materials. Ultrasonic thermal welding by the third phase (TWTP) method was proposed in combination with the formation of a third phase, which was confirmed as an effective technology for polymer welding between the two dissimilar materials compared with the traditional USW. This review focused on the advances of applying the ultrasonic TWTP for thermoplastic materials. The research development on the ultrasonic TWTP of polycarbonate (PC) and polymethyl methacrylate (PMMA), polylactic acid (PLA) and polyformaldehyde (POM), and PLA and PMMA are summarized according to the preparation of the third phase, welded strength, morphologies of rupture surfaces, thermal stability, and others. The review aimed at providing guidance for using ultrasonic TWTP in polymers and a basic understanding of the welding mechanism, i.e., interdiffusion and molecular motion mechanisms between the phases.

Keywords: thermal welding by the third phase (TWTP); thermoplastic welding technology; ultrasonic welding (USW); welding between dissimilar materials.

Figure 1

Schematic illustration of USW method. Adapted from Reference [106].

Figure 2

Conventional USW methods. Adapted from Reference [99].

Figure 3

Schematic drawing of determination of amplitude transmission using a tilted sensor. Adapted from Reference [136].

Figure 4

Power and travel curves as function of energy for the initial weld, produced with a travel of 0.5 mm. Adapted from Reference [142]. (A) intact EDs; (B) collapse of EDs due to melting; (C) partial flow of the EDs and melt-front arrest; (D) remelting of ED melt-fronts and subsequent flow out of the overlap; (E) complete ED squeeze out from the welding interface, with melt and partial flow of the matrix beyond the first adherend layer.

Figure 5

Schematic illustration of joint configuration USW (dimensions in mm). Adapted from Reference [144].

Figure 6

Illustration of polymer using (a) conventional and (b) composite film USW. Adapted from Reference [145].

Figure 7

Welding principle schematic drawing followed by ultrasonic TWTP technology. Adapted from Reference [146,147].

Figure 8

Schematic diagram of IPS preparation for PC-PMMA weld. Adapted from Reference [148].

Figure 9

Nominal stress-strain curves of PC, PMMA, PC/PMMA composite and IPS. Adapted from Reference [149].

Figure 10

Welded strengths at different welding times. (a) Nominal stresses and strain at different welding times under welding pressure of 0.4 MPa; (b) Welded strengths at different welding times. Adapted from Reference [149].

Figure 10

Welded strengths at different welding times. (a) Nominal stresses and strain at different welding times under welding pressure of 0.4 MPa; (b) Welded strengths at different welding times. Adapted from Reference [149].

Figure 11

SEM images of ruptured surfaces of welded interfaces of PC side under welding pressure of 0.3MPa. (a), (b), (c) are under welding time of 1.5 s, 3 s and 4 s. Adapted from Reference [149].

Figure 12

Welded strengths at different welding pressures. (a) Nominal stress and strain at different welding pressures under welding time of 2 s; (b) Welded strengths at different welding pressures under welding times of 2 s and 3 s. Adapted from Reference [149].

Figure 13

SEM images of rupture surfaces under welding time of 3.0 s. (a) and (b) are at welding pressures of 0.1 MPa and 0.4 MPa. Adapted from Reference [149].

Figure 14

TG test of PC, PMMA and PC/PMMA. Adapted from Reference [149].

Figure 15

Welded strengths of PLA and POM at different welding times under welding pressure of 0.4 MPa. Adapted from Reference [150].

Figure 16

Welded strengths at different welding times under welding pressure of 0.3 MPa. Adapted from Reference [150].

Figure 17

Rupture surfaces of welded interface between POM and PLA under welding pressure of 0.4 MPa. (a) is POM side at welding time of 1 s, (b) is PLA side at welding time of 1 s, (c) is POM side at welding time of 2 s and (d) is PLA side at welding time of 2 s. Adapted from Reference [150].

Figure 18

Tensile strengths of matrices and PLA/PMMA blends. Adapted from Reference [148].

Figure 19

Tensile strengths of matrices and PLA/PMMA blends. Adapted from Reference [148].

Figure 20

TG analysis of PLA, PMMA, and PLA/PMMA blends of 1:1. Adapted from Reference [151].

Figure 21

Welded strengths at different welding times under different welding pressures (P). Adapted from Reference [151].

Figure 22

SEM images of rupture surfaces under welding pressure of 0.3 MPa and welding time of (a) 1 s, (b) 2 s, (c) 3 s and (d) 5 s. Adapted from Reference [151].

Figure 23

Schematic drawing of macromolecular inter-diffusion of IPS and WPs. Adapted from Reference [147]. Temperatures of the interfaces are (a) under room temperature; (b) higher than glass transition temperature; (c) above melting point; (d) back to room temperature.