STRUCTURE-PROPERTY RELATIONSHIPS OF CASTOR OIL-BASED POLYURETHANE FOAMS
STRUCTURE-PROPERTY RELATIONSHIPS OF CASTOR OIL-BASED POLYURETHANE FOAMS
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Date
2016-12
Authors
ABDULAZEEZ, KANKIA YUSUF
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Abstract
Mechanically extracted castor oil (CO) from the seeds of Nigerian wild castor plant (Ricinus communis Linn) was used after purification and chemical modification by PCl5-chlorination and by lead (II) oxide (PbO)-catalysed glycerolysis. FTIR and GC-MS techniques were used for the structural characterisation of the neat and modified polyols, while titrimetric methods were used to determine their physico-chemical characteristics. Using two different formulations of isocyanate/polyol (NCO/OH) ratios of 1/2 and 1/1, rigid, semi-rigid and flexible CO-based polyurethane foams (COPUFs) were prepared by one-shot method. Foam reaction involved either neat CO or its modified polyols containing varying concentrations (10-60 wt%) of the modifier, and 80:20 mixture of 2,4- and 2,6-toluene diisocyanate (TDI) at room temperature (30-350C). Foam reaction took place in presence of stannous octoate and dimethylaminoethanol (DMAE) catalysts, methylene chloride (physical blowing agent) and silicone oil (surfactant). In addition to the basic foam formulation, CaCO3-filler (2-20 wt%) was incorporated in selected sample preparations. Heptachlorotetradecane (HCTD) and heptachloroheptadecane (HCHD), two medium (straight)-chain chlorinated paraffins, were also incorporated in selected preparations as plasticisers and flame retardants (FRs) either singly or as blends of different weight ratios. All foams obtained were characterised in terms of their process parameters such as cream time, free-rise time, gel time, tack-free time and foam rise (ASTM D7487) as well as their physico-mechanical properties namely: density (ASTM D1622-08), water absorption (ASTM D570-98/D2842-12), compressive strength (ASTM D1621-10) and creep recovery (ASTM D2990-09). The structure-property relationships of COPUFs were established through process; physico-chemical, mechanical, morphology and flammability parameters. Glycerol-modified foams (GMFs) were found to be rigid and
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moisture resistant, with their densities varying from 24.50-50.50 kg/m3; water absorption (0.73-2.20 wt%); compressive strength (89.20-450.20 KN/m2) and creep recovery (18.5-28.5%). Rigidity in the structure of GMFs increased with modifier concentration and at higher NCO/OH ratios. GMF rigidity was attributed to network formation likely resulting from allophanate and urea crosslinking reactions during foam synthesis. CaCO3-filled foams (CFFs) have shown improvement in moisture resistance, density and compressive strength, but reduction in creep recovery compared to the control (neat) COPUF, with further property enhancements as filler loading was increased from 2-20 wt%. HCTD/HCHD plasticised COPUFs were found to be soft, flexible foams, especially at the lower NCO/OH ratio of 1/2, and at 50:50 (HCTD: HCHD) weight ratios. Foams were also characterised in terms of their flammability properties. Flame properties studied were ignition time (IT), flame propagation rate (FPR) and after-glow time (AGT). Results indicate that IT is closely related to the density of COPUF matrix. Additives (other than plasticisers) generally improved the density, compressive strength or fire retardancy characteristics of the COPUFs. FR treatment of COPUFs has revealed HCTD as a more effective individual FR than HCHD. This is explained in part in terms of greater absorbability (higher add-on) of HCTD in the COPUF system, and also in terms of a vapour phase radical quenching mechanism of action by which the shorter chain and more thermally unstable HCTD released more chlorine radicals per mole than HCHD, thus giving the former early and greater arrestive power of COPUF combustion processes. Microstructural imaging of foams using scanning electron microscopy (SEM) has revealed wide variation in pore size (0.10-0.35 mm) and shape (spherical, oblong and polyhedral), while wall thicknesses ranged from 18-50 μm.
Description
A Thesis submitted to the School of Postgraduate Studies, Ahmadu Bello University, Zaria, in partial fulfillment of the requirements for the Award of the Degree of Doctor of Philosophy (Ph.D) in Polymer Science and Technology. Department of Chemistry, Ahmadu Bello University, Zaria, Nigeria.
Keywords
STRUCTURE-PROPERTY,, RELATIONSHIPS,, CASTOR OIL-BASED, POLYURETHANE FOAMS