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Some exploratory work was done to look at novel applications, such as filler use and comonomers, for lignin in thermosetting unsaturated polyesters and vinyl esters. The solubility of different lignins (pine kraft, hardwood, ethoxylated, and maleinated) was determined in different resin systems (acrylated epoxidized soybean oil, hydroxylated soybean oil, soy oil monoglyceride, and a commercial vinyl ester) to give an idea of the compatibility of lignin with the resin systems that were used. Further, the use of lignin as a filler was studied. An increase in the glass-transition temperature was noticed, and the modulus at 20°C decreased because of the plasticizing effect of lignin. The lignin was modified to improve its effect on the matrix properties by adding double bond functionality, thus making it possible to incorporate the lignin molecule in the resin through free-radical polymerization. Modified lignin was introduced in several resins by a reaction with maleic anhydride and epoxidized soybean oil and was tested for its effect on the solubility, glass-transition temperature, and modulus. This modification improved the solubility of lignin in styrene-containing resins, as well as the chemical incorporation of lignin in the resin. Moreover, lignin was used to treat the surfaces of natural hemp fibers to utilize lignin's natural affinity for cellulosic fibers. The idea was to cure the surface defects on the natural fibers and increase the bonding strength between the resin and fiber. An optimum improvement was noticed that depended on the amount of lignin covering the fibers.

In the Affordable Composites from Renewable Resources (ACRES) program at the University of Delaware, soybean oil and other plant triglycerides have been made amenable to polymerization using a broad range of chemical routes. The resultant polymers range in properties from soft rubbers to hard thermosets for composite applications. In this paper we present an investigation of the mechanical properties of glass/flax hybrid composites based on these thermoset matrix materials. Composites with different glass/flax ratios and different fiber arrangements were made using a modified soybean oil matrix material. The fiber arrangement was varied to make symmetric and unsymmetric composites. The latter were tested in different modes in flexural tests and drop weight impact tests. The mechanical properties of the composites were found to depend upon the glass/flax ratio and the arrangement of fibers in the composite. On proper selection of the arrangement of fibers in the composite, the glass fibers and flax fibers were found to act synergistically resulting in an improved flexural and impact performance. POLYM. COMPOS., 26:407–416, 2005. © 2005 Society of Plastics Engineers

Different factors important in ascertaining the thermoformability of polymeric materials are identified and defined. These include resistance to sag, ease of flow, mold replication, deep draw capability, sensitivity to thermoforming temperature and speed, uniformity of thickness distribution, and post‐forming shrinkage and dimensional stability. Methods to study these properties can be classified into small deformation and large deformation methods. The small deformation methods, which are the subject of this paper, include dynamic temperature sweep tests, dynamic frequency sweep tests, stress relaxation time, and creep recovery tests. These tests were used to compare the thermoformabilities of a blend of polyphenylene ether (PPE) and polypropylene (PP) and thermoformable acrylonitrile butadiene styrene (ABS) resin. The dynamic temperature and frequency tests showed that the PPE/PP blend generally has a better viscoelastic balance than ABS implying a better balance between resistance to sag and ease of flow. Creep recovery tests suggested that the PPE/PP blend may offer better mold replication during thermoforming. Studies based on the stress relaxation time showed a lower residual stress build‐up in thermoformed PPE/PP blend than ABS implying better dimensional stability and a higher in‐service temperature window for the thermoformed PPE/PP blend than ABS. POLYM. ENG. SCI., 45:1369–1376, 2005. © 2005 Society of Plastics Engineers

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Thermoforming involves stretching of a heat‐softened polymer sheet to large strains. This was simulated by uniaxial tensile stretching (UTS) experiments at different temperatures and strain rates. These experiments were used to identify an optimum window of thermoforming temperature and strain rate and to compare the thermoformabilities of a blend of polyphenylene ether (PPE) and polypropylene (PP) with thermoformable acrylonitrile butadiene styrene (ABS) resin. It was shown that the PPE/PP blend generally has a wider thermoforming window than ABS. Using Considere construction, it was shown that the PPE/PP blend underwent more homogeneous deformation than ABS. The higher homogeneity in deformation of the PPE/PP blend resulted in a higher uniformity in the distribution of draw ratios, which implies more uniform thickness distribution in thermoformed parts. Draw ratio and crystallization studies ruled out the possibility of postforming shrinkage in the PPE/PP blend under ambient temperature conditions. The PPE/PP blend was also found to have a higher shrinkage onset temperature than that of ABS. An attempt was also made to relate the small deformation viscoelastic properties with the large deformation UTS properties through the use of Deborah numbers. These results bring out the importance of studying both the small deformation and large deformation properties in conjunction, while comparing the thermoformabilities of different polymers. POLYM. ENG. SCI., 45:1377–1384, 2005. © 2005 Society of Plastics Engineers

Recent advances in genetic engineering, composite science, and natural fiber development offer significant opportunities for new, improved materials from renewable resources that can biodegrade or be recycled, thus enhancing global sustainability. A wide range of high-performance, low-cost materials can be made using plant oils, natural fibers, and lignin. By selecting the fatty acid distribution function of plant oils via computer simulation and the molecular connectivity, we can control chemical functionalization and molecular architecture to produce linear, branched, or cross-linked polymers. These materials can be used as pressure-sensitive adhesives, elastomers, rubbers, and composite resins. This chapter describes the chemical pathways that were used to modify plant oils and allow them to react with each other and various co-monomers to form materials with useful properties.

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