Abstract
Rigid low-density closed-cell polyurethane (PU) foams are widely used in both thermal insulation and structural applications. The sustainability of PU foam production can be increased by using bio-based components and fillers that ensure both enhanced mechanical properties and higher renewable material content. Such bio-based foams were produced using polyols derived from rapeseed oil and microcrystalline cellulose (MCC) fibers as filler. The effect of MCC fiber loading of up to 10 wt % on the morphology, tensile stiffness, and strength of foams has been evaluated. For estimation of the mechanical reinforcement efficiency of foams, a model allowing for the partial alignment of filler fibers in foam struts was developed and validated against test results. It is shown that although applying MCC fibers leads to modest gains in the mechanical properties of PU foams compared with cellulose nanocrystal reinforcement, it may provide a higher content of renewable material in the foams.
Highlights
Rigid polyurethane (PU) and polyisocyanurate (PIR) foams have found diverse applications in construction, transport, and appliance industries, where their remarkable functional and structural properties are exploited
The polyol system of foams incorporated both polyols derived from rapeseed oil (RO) by amidization with diethanolamine employing zinc acetate as a catalyst (70 pbw) and higher functional polyether polyols based on sorbitol Lupranol 3422 (30 pbw) purchased from BASF
The reinforcement efficiency factors Equations (5) and (9) enable the separation of the purely mechanical effect of reinforcing particles on foam stiffness and strength from that caused by alteration in foam density and morphology, whereas Equations (4) and (8) provide a link between foam reinforcement efficiency and the properties of the solid composite material forming cell struts
Summary
Rigid polyurethane (PU) and polyisocyanurate (PIR) foams have found diverse applications in construction, transport, and appliance industries, where their remarkable functional and structural properties are exploited. The intermolecular interactions and higher packing of polymer chains usually improve the mechanical properties of PU elastomers and flexible PU foams, whereas the high degree of cross-linking in rigid PU foams hampers the intermolecular conformation of polymer chains Both the strength and stiffness of rigid PU foams can be increased by filling the polymer with micro/nano-size particles, such as nanoclays and carbon nanotubes [5,6], glass fibers [7,8], and carbon fibers [9]. The effect of MCC fiber filler on the tensile strength and stiffness of rigid low-density bio-based PU foams is studied experimentally, complementing studies of the response of composite foams in compression [15,16,17]. Analytical models for the reinforcement efficiency of foam stiffness and strength reflecting the filler alignment in foam struts are developed and validated
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