Differential shedding: A study of the fiber transfer mechanisms of blended cotton and polyester textiles

One of the primary interests of forensic sciences is the study of traces, better conceived as silent witnesses to criminal activity whose existence is attributable to Locard's principle. Thus, textile fibers are commonly exploited as they are easily transferred during contact which can vary in intensity depending upon the type of activity that occurred. Regardless, current knowledge pertaining to fiber transfer mechanisms, particularly in regards to blended textiles, is limited. It is recognized that the intensity of the contact, the type of textile as well as the size and type of fibers composing it have a significant influence on the amount of fibers transferred. However, when the donor textile is blended (eg. 50% cotton, 50% polyester), it often happens that one of the two types of fibers is transferred in greater proportion to the receiving surface (eg. 80% cotton and 20% polyester). The percentages indicated on the manufactured label are however not representative of the respective proportions (based on the number of fibers) of each type of fiber composing the fabric, but rather the weight of each respective type of fiber used to fabricate the garment. Therefore, the amount of collected fibers (traces) cannot be easily correlated to the proportions indicated on the manufactured label used to describe the textile. The objective of this study was to test the transfer capacities of blended textiles of different cotton and polyester proportions by performing several simulations under controlled conditions (i.e. contact between two textiles with a constant force and speed). The results were then correlated to the fiber type, morphology, and size. Overall, the project contributes to improving the comprehension of fiber transfer mechanisms, and provides insight on the quantity and the proportions of fibers capable of being transferred between the donor and the recipient textiles following a specific type of action and contact (legitimate or otherwise).