Observations of the Physical and Mechanical Properties of the Natural Polymer Yop
Authors:Greg Barker, Casey Directo, Antonio Jauregui, Jerry Le, Stephen Moser
Mentor:Vilupanur Ravi, Chair of the Chemical and Materials Engineering Department , California State Polytechnic University Pomona
For centuries the Chumash tribe inhabited the coast of central and southern California and traveled along the coastline in seafaring canoes called tomols. These tomols were made of wooden planks bound together with natural fibers and sealed with an adhesive termed yop. Yop is a blend of pine pitch and a naturally occurring tar derivative called asphaltum. The composition of yop has not yet been quantified. Our hypothesis in regards to the original composition of yop is that the Chumash chose this natural adhesive blend because of the flow properties and the resulting strength, adhesive properties, and ease of use. The yop and asphaltum used in these experiments were collected from the Santa Barbara area. In an attempt to solve the mystery of the original yop composition, we have studied the chemical composition of this polymer utilizing X-ray diffraction, Fourier Transform Infra-red Spectroscopy (FTIR) and the mechanical properties of this material. Many different compositions were tested and results show that adhesive test specimens containing 30wt% pine pitch in the blend have the highest shear failure strength with increases in pine pitch reducing strength. Comparisons of this ratio were made to archeological samples, which has given us some insights into why the Chumash used this natural polymer for their canoes. Based on preliminary testing, it has been observed that for asphaltum-pine pitch mixtures containing 15-35% pine pitch there is a critical region where the viscosity of the yop changes dramatically. To further understand the strength of the material in this critical region we will be studying its viscosity and viscoelastic properties using various yop compositions in more depth as well as studying the optical characteristics under polarized light. Future work will involve the development of a functional rheometer to study the polymer and the underlying organic chemistry.