The morphology of sheep wool applied as organic fertilizer biodegraded in the soil was examined. The investigations were conducted in natural conditions for unwashed waste wool, which was rejected during sorting and then chopped into short segments and wool pellets. Different types of wool were mixed with soil and buried in experimental plots. The wool samples were periodically taken and analyzed for one year using Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray Spectroscopy (EDS). During examinations, the changes in the fibers' morphology were observed. It was stated that cut wool and pellet are mechanically damaged, which significantly accelerates wool biodegradation and quickly destroys the whole fiber structure. On the contrary, for undamaged fibers biodegradation occurs slowly, layer by layer, in a predictable sequence. This finding has practical implications for the use of wool as an organic fertilizer, suggesting that the method of preparation can influence its biodegradation rate. (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(SEM)(sic)(sic)(sic)(sic)(sic)X(sic)(sic)(sic)(sic)(EDS)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic). (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic), (sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic)(sic).

Although natural fibers (NFs), among which animal fibers (AFs) are found, have been used for millennia as reinforcement scheme of some construction materials (CMs), it is not until recent decades when scientific studies have been carried out to quantitively evaluate the impact of adding NFs into CMs, but with a special focus on vegetal fibers (VFs) over AFs. Nevertheless, there have been several studies addressing the use of AFs in different CMs and, therefore, the need of a systematic review study is evident. To contribute to this research gap, this paper presents a comprehensive review study addressing available scientific information of different types of AFs (e.g., sheep wool fibers (SWFs), chicken feathers fibers (CFFs), human hair fibers (HHFs), pig hair fibers (PHFs), silk fibers (SFs), and dog hair fibers (DHFs)) and also their use in four specific different CMs matrices (i.e., cementitious, gypsum, soil and polymer matrices). This comprehensive search was conducted in Web of Science and Science Direct, two of the largest and more prestigious scientific databases, using specific keywords and Boolean operators and the selection of the papers was based on the provision of enough quantitative information of the mixtures (e.g., specific characteristic and dosages of AFs and matrix used) as well as experimental findings. As a result of this study, organized, summarized and sufficient information is provided to support the positive use of AF as reinforcement scheme to improve some physical/thermal/mechanical/ damage/durability properties of CMs by taking advantage of the abundance of these resources worldwide. Moreover, the use of AFs might also provide environmental benefits and cost reductions, which are global objectives within the construction sector. Finally, this review study found that there are still several research gaps in the use of particular AFs (e.g., DHFs) as well as combinations between the AFs and the CMs addressed in this study (e.g., effects of PHFs in polymer matrices) and these gaps are recommended as future studies.