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Foam Look Out for Pines

Foam Look Out for Pines Tall oil (liquid rosin) as source for PUR and PIR foams Article contributed by Dr. Ugis Cabulis, Mikelis Kirpluks Latvian State Institute of Wood Chemistry Riga, Latvia Prof. Andrea Lazzeri University of Pisa Pisa, Italy Table1: Characteristics of two PUR foams obtained from tall oil. Density, kg/m 3 30 45 Compressive strength, MPa 0.15 0.25 Youngs modulus, MPa 3.0 4.3 Closed cell content, % 92 95 Water abs. 7 days, vol.% 2.2 1.7 Figure 4: Filled T-piece for cars. Rigid PU, content of renewable materials = 24%. The abundance of hydroxyl-containing materials in nature makes them an apparently obvious fit as the polyurethane industry seeks to incorporate bio-renewable materials into its products. Hence the EU 7 th FP Forbioplast project (Forest Resource Sustainability through Bio-Based-Composite Development), coordinated by Prof. Andrea Lazzeri, comprises one research area that looks into the use of tall oil as a renewable source in rigid polyurethane (PUR) and polyisocyanurate (PIR) foam production and also into natural fibers as a reinforcement material. Nowadays, most raw materials still used for the production of polyurethane chemicals are products of petrochemical origin. Renewable resources could provide not only a sustainable material source but also a stable material price. A part of the raw materials needed for the production of bio-based PUR foams can be obtained from renewable resources such as different types of vegetable oils or tall oil, a by-product of pulp production. The forest biomass represents abundant, renewable, nonfood competition and a low cost resource that can play an alternative role to petroleum resources. The production and use of the forest biomass energy is ‘greenhouse gas’ neutral, while the expansion of plantation forestry is a positive benefit to greenhouse gas reduction through increasing forests as a carbon sink. Consequently the Forbioplast project, for example, aims at the general assessment of forest resources for the production of bio-based products, the development of improved technologies with regard to the present industrial synthesis of polyurethane and the scale-up of such processes or the replacement of glass fibers and mineral fillers with wood-derived fibers in automotive interiors and exterior parts, and the development of biodegradable polymer/wood derived fiber composites for applications in the packaging and agriculture sectors. One topic of the research activity is focused on the use of wood, pulp and paper mill by-products (bark, chips, sawdust, black liquor and tall oil) as raw materials for the production of polyurethane foams by an innovative sustainable synthetic process with reduced energy consumption. A technology of the synthesis of polyols with the hydroxyl value 200 – 360 mg KOH/g from different grades of tall oil by way of esterification or amidization has been developed. PUR and PIR foams were obtained and their physical, mechanical and thermal characteristics were tested (see table 1). The maximum content of renewable resource in ready foams is 26%. In contrast to PUR and PIR foams, which are obtained from the polyols synthesized from petrochemical products, the polymeric matrix of these foams is characterized by the absence of ester and ether groups in the polymeric main chain, as well as the presence of long saturated and unsaturated fatty acid C 12 – C 22 side chains. This peculiarity of the chemical structure ought to promote the decrease in the water absorption of these foams, so that the thermal insulation would be of a high performance for a long term. For the same reason, the foams should be more stable to hydrolysis. Apart from this, long side chains are capable of screening the polar urethane and isocyanurate groups and 42 bioplastics MAGAZINE [01/11] Vol. 6

Foam Fig. 1: Compression strength and Young’s modulus of PU foams filled with cellulose fibers. Foam density 25 – 30 kg/m3. promoting the intermolecular plasticization of the polymeric matrix. As a result of this plasticization the friability of the PIR foams should decrease. When using biopolymers as a matrix a logical consequence is to reinforce them with natural fibers (NF). Along with it come the advantages of significant weight and cost savings and the replacement of petrochemical raw materials. The NF properties are affected by many factors such as variety, climate, harvest, maturity, and degree of retting. For this reason four different NFs were tested: cellulose, wood, flax and modified cellulose. Whereas the graphics only present PU foams filled with cellulose fibers, the trends for other NFs are similar. The samples for the tests were obtained by hand-mixing. The main characteristics of the cellulose NF used are humidity – 4.5%; free OH-content on the surface – 320 mgKOH/g; aspect ratio – 263 mm / 64mm = 6.7. Figure 1 shows that compressive strength and Young’s modulus for lightweight foams decrease with increasing filler content. At the same time, there are no significant changes in the closed cell content and water adsorption. For PU foams with a density 40 - 45 kg/m 3 (figure 2), compressive strength is in balance and does not depend on the filler concentration; there is a slight increase in the Young’s modulus in the direction parallel to foaming. Both thermoinsulation PU foam series are closed cell foams. The renewable raw material content in the foam formulations could reach 35%. On the other hand, the foams with a density >200 kg/m 3 , obtained in a closed mould, show an increase in compression strength and Young’s modulus (Fig.3) with the optimum filler concentration in ready foams of 3 - 6%; in this case, the renewable materials content is about 30%. Polyol synthesis, based on tall oil, is an environmentally friendly process with low energy consumption and the obtained polyols are competitive with those synthesized from petrochemical raw materials. Further process optimization for machine production of filled foams is one target of future work, as well as the selection of the optimum fibers from cellulose, wood and modified cellulose fibers. Current activities aim at modifying fibers by enzymes in order to improve the fiber / PU matrix adhesion. This will lead to the improvement of the mechanical characteristics of rigid foam even at low and medium densities. Finally, the polyol synthesis, foam preparation and PU filling process remains an area for investigation regarding improved processing for further scalingup and industrialization. This work is supported by European Community grant FORBIOPLAST No.KBBE- 212239 σ,MPa E,MPa 0.2 0.15 0.1 0.05 Compression strength, MPa Parallel foaming Perpendicular foaming 0 0 5 10 Filler content, % 4 3 2 1 Young modulus, MPa Parallel foaming Perpendicular foaming 0 0 5 10 Filler content, % Figure 2: Compression strength and Young’s modulus of PU foams filled with cellulose fibers. Foam density 40 – 45 kg/m3. σ,MPa E,MPa 0.3 0.2 Compression strength, MPa 0.1 Parallel foaming Perpendicular foaming 0 0 5 10 Filler content, % 8 6 4 2 Young modulus, MPa Parallel foaming Perpendicular foaming 0 0 5 10 Filler content, % Figure 3: Compression strength and Young’s modulus of PU foams filled with cellulose fibers. Foam density 220-250 kg/m3. σ,MPa E,MPa 2 1.5 1 Compression strength, MPa 0.5 Parallel foaming Perpendicular foaming 0 0 5 10 Filler content, % 50 25 Young modulus, MPa Parallel foaming Perpendicular foaming 0 0 5 10 Filler content, % bioplastics MAGAZINE [01/11] Vol. 6 43

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