Polymers: Strength Variation with Additives Ariunaa Bayarbat, Scott Steffin, and Travis Yaeger SRJC Engr 45 12/05/05 Instructor: Younes Ataiiyan

How do different additions to a polyester polymer affect its strength?

Polymers Monomer – The basic building block of a polymer – The smallest repeating unit in a polymer chain – A polymer has a linear, branched, or network structure of chained monomers

Polymerization – Initiation: Creation of the free radical, giving instability to a monomer – Propagation: Monomer additions to the chain, passing along instability – Termination: Removal of instability (free radical) through combination with another unstable chain or impurity, or passage of instability to another monomer

Polymers form a network of interconnected branches, like knots, held together by hydrogen bonding and weak forces Resin – “Any of numerous physically similar polymerized synthetics or chemically modified natural resins including thermoplastic materials such as polyvinyl, polystyrene, and polyethylene and thermosetting materials such as polyesters, epoxies, and silicones that are used with fillers, stabilizers, pigments, and other components to form plastics.”

Polymer Categories Thermoplastic Thermoset – Thermoset polymers get hard and rigid upon heating – They retain their shape once they are cooled – They have network molecular structures – The polymerization process is enhanced by higher temperatures and it is not reversible

Polyester Thermoset Casting Resin Reasons for choosing – Inexpensive – Clear – Easy to make samples – Thick enough for tests

Experiment Base sample – We mixed 100 g of the resin with 28 drops of the catalyst MEKP (Methyl Ethyl Ketone Peroxide) – We poured it into a mold of 5”x 4.5” – Samples were about 0.25” thick Four different samples with additions – 2.5 g of sawdust – 2 g of vitamin C (from vitamin C tablets) – 5 g of cornstarch – 28 more drops of the catalyst

We let the samples set for a week We cut them into small pieces and uniform thickness We performed a compression test on the samples

Analysis Theoretically, the base sample was supposed to have the lowest strength because the additives caused more strength The data show the base sample having the greatest strength Real conclusions cannot be drawn from the data because of the many variables besides just the additions

Conclusions The result was different from what we expected The reasons for inconclusive results – Different sample areas – Different sample thicknesses – The uneven testing surface Things we would do differently – Uniform size for all samples – Much greater percentage of additions in each sample – Use better testing surface

Resources Shackelford, James F. Introduction to Materials Science for Engineers. Upper Saddle River, NJ: Pearson Education Inc.,