# Additively Manufactured Polymers for Electronic Components
## 3 Polymers Used for AM in Electronic Applications
### Extrinsically Conductive Polymers (ECPs)
#### 3.2.2 Graphene  
Graphene is the strongest nanomaterial reinforcement [101], showing a two-dimensional structure of sp\({}^{2}\) hybridised carbon atoms arranged in a hexagonal lattice. Graphene acts as the fundamental structural component in various carbon allotropes, including carbon nanotubes, graphite, fullerenes, and others. As a nanomaterial, graphene exhibits a wide range of properties that extend beyond specific domains. It is renowned for displaying phenomena such as the room-temperature quantum Hall effect, carrier mobility [102], and the degeneration of valence and conduction bands at the K-point (Brillouin zone). These properties can be modified by altering the deposition of layer-by-layer graphene sheets, akin to the structure of graphite. In terms of electronic properties, bi-layer graphene demonstrates parabolic electronic bands with an open energy gap [103], while tri-layer graphene exhibits a combined band structure. The number of layers is crucial in changing the electrical properties of graphene, as an increase in the number of layers leads to valence band-conduction band overlapping [104]. Reinforcement in polymer composites can be obtained using graphene and exploiting its remarkable properties [105]. [PERSON] and colleagues demonstrated that composite structures can be created through 3D printing using a graphene loading of up to 5.6 wt% [106]. [PERSON] et al. developed a polymer-graphene composite for direct 3D printing using a solution-based approach, achieving a high electrical conductivity of 4.76 S cm\({}^{-1}\) with 6 wt% graphene. The printing process aligned the graphene, enhancing conductivity due to the preferential orientation of the graphene particles during the process [107]. These graphene composites enabled the production of flexible printed circuits with strong interlayer bonding strength and mechanical durability in both axial and transverse directions [108]. Three-dimensional-printed samples of poly(lactic acid) and polypropylene filled with 20% graphene nanoplatelets exhibited  
Figure 7: **(a)** A representative diagram of the DLP 3D printing process, along with a 3D hexagonal structure that has a thickness of 5 mm and contains 0.1 wt% carbon nanotubes (CNTs) as the finished part. **(b)** A circuit-like structure built on an insulating base made from a mixture of PEGDA and PEGMEMA in a 1:1.5 weight ratio, with brilliant green colourant. The structure features suspended elements that also contain 0.1 wt% CNTs, with dimensions of 30 \(\times\) 50 mm. Adapted and reprinted with permission from ref. [96]. an electrical conductivity of up to 5 S cm\({}^{-1}\)[109]. Acrylic and epoxy polymers are the most commonly used resins for SL technology and, when combined with graphene-based filler, the resolution and the quality of SL-printed parts are affected by the curing strategy, laser intensity, exposure duration, and scan speed [110]. Whereas the addition of photoinitiators and UV absorbers controls the depth of polymerisation [111]. Although SL offers several advantages compared to other AM technologies, including high-resolution printing and nozzle-free processing, SL has some drawbacks if graphene-based inks are used, including issues with graphene dispersion and stability, curing compatibility, limited layer thickness, and material uniformity [110]. SL encompasses various printing methods, such as single vector array, DLP, continuous liquid interface production, and two-photon greyscale lithography. Graphene-based inks are known for their ink formation characteristics, mechanical durability, and excellent conductivity [107]. In this context, graphene oxide (GO) offers advantages over pristine graphene due to its easier production, hydrophilic functional groups, and the possible large-scale incorporation of active materials [112]. GO dispersion in water is a key factor in enhancing ink printability. When GO is uniformly dispersed in water, it creates an isotropic dispersion with characteristics like a nematic liquid crystal [110].