## 3 Research Area and General Purpose of Study  
The aim of this article is to provide a comprehensive review of the most common and current chain solutions used in civil and urban engineering. In addition, the study addresses the issue of recycling selected polymers as a potential source of advanced materials for the production of load-bearing polymer composite chains.  
A key point is to highlight the potential contribution of ongoing research conducted under the LIDER 14/0270/2023 project titled: \"Composite non-conductive chain with an anchoring system\". The use of recycled materials -- particularly fiber-reinforced polymers-- offers a promising alternative to traditional structural materials. This direction aligns with the need to reduce carbon footprints and increase resource efficiency, in accordance with modern engineering practices in which environmental considerations play a central role.  
Research in the area of alternative materials indicates a largely untapped potential for meeting rigorous technical requirements in specific applications. With the support of modern processing and shaping technologies, it is now possible to develop materials that are more sustainable, cost-effective, and environmentally friendly. This is especially relevant in the context of the Single-Use Plastics Directive, which restricts the use of disposable plastic products. Innovative approaches to material design can help address the challenges posed by such regulations and create new opportunities for more sustainable industrial solutions.  
Modified materials used for the manufacture of technical composite chains can feature high mechanical strength as well as specific functional properties, such as luminescence, electrical insulation, and flame retardancy.  
In today's world, solving unique engineering challenges within short timeframes presents a significant difficulty. As knowledge evolves within specific fields, it is important to explore whether materials currently known and available in other sectors may be repurposed for novel or unconventional technical solutions. The chain industry continues to generate high material demand and may effectively utilize substances that are considered waste in other sectors.  
The article addresses the following issues:  
* Types, materials, and applications: A classification of chains is provided based on type, material, and intended function, with an emphasis on their wide use across various industrial sectors. The importance of proper material selection is discussed in relation to durability, strength, and corrosion resistance. The role of modern plastics and composites is also highlighted, especially in terms of improving energy efficiency and supporting sustainable industrial development.  
* Basic requirements and dimensioning: A compilation of selected standards related to the manufacturing and design of steel chains is presented. However, such standards are lacking for chains made of other materials, particularly polymers. A sample description of the design and fabrication of a link chain is included.
* Shaping and geometry: The geometry of chain links plays a critical role in their strength and functionality. Properly designed link geometry reduces stress concentrations and deformation, thereby enhancing the chain's longevity. Numerical simulations enable precise optimization of link shapes, reducing the risk of mechanical failure.  
The subject matter discussed in this paper falls within the domain of Engineering and Technical Sciences, particularly civil engineering, geodesy, and transportation; environmental engineering, mining, and energy; chemical engineering; materials science; and mechanical engineering.