Mechanical and Physical Properties of Glass Wool-Rigid Polyurethane Foam Composites

Al-Nahrain University, College of Engineering Journal (NUCEJ) Vol.18 No.1, 2015 pp.41 - 49

Ismail Ibrahim Marhoon* Aseel Kais Rasheed Material Engineering Department/ College of Ministry of science and technology / Renewable Engineering/Al-Mustansiriya Energy Directorate University/Baghdad *E-mail: [email protected]

Abstract foams are obtained by the reaction of isocyanate This research is devoted to the preparation of with polyols, which, depending on the foam polymer matrix composite materials by formulation, regulate the properties of the forming in place method, where the composite material. Their foaming is possible due to the foam material was prepared from the rigid in situ generation of a foaming agent during the polyurethane foam (PU) as a matrix reinforced by exothermal polymerization reaction, leading to glass wool insulator with weight fractions (2%, crosslinked foams with changeable cellular 4%, 6%, 8% and 10%) .Several mechanical and structures[5]. Depending on the amount, physical tests were done and these include impact, proportions and characteristics of the components, flexural, compression, hardness, density, water it is possible to obtain three categories of absorption and thermal conductivity. The result polyurethanes foams which are flexible shows that the values of mechanical and physical polyurethanes, semi rigid polyurethanes and rigid properties in general are increased with the polyurethanes with different densities and cellular increase of glass wool weight fraction content. structures, and thus adjustable properties [5, 6]. The values of flexural strength decrease with the Besides, given that both basic components are increase of weight fraction of glass wool fiber liquid at room temperature, it is relatively after 8% wt. easy to incorporate ﬁllers and reinforcements further, extending the applicability of these Keywords- Rigid polyurethane foam, Glass lightweight materials [7]. wool, foam composite, density, thermal Glass wool insulation is felt materials made of conductor, flexural strength, hardness, impact glass with binder by heating and solidifying. It strength, water absorption, polyol-isocyanate. has good flexibility, affordable price and it is easy to install. Features of fiber glass wool are nature 1. Introduction products, acoustical absorption, high thermal In a country like Iraq, where large seasonal resistance with low thermal conductivity variations in temperatures occur, thermal (Working temperature at about 450 ºC), fire safe insulation is quite important. Though designing materials and environmental friendly materials [8- the building for obtaining thermal and sound 12]. Typical final nominal fiber diameters range insulation characteristics involves additional from 4 µm to 15 µm. and softening point is 675 expenditure, it is well compensated by the ºC [13]. comfortable and healthy environment obtained. Composite polymer foams are materials of a The polyurethanes (PU) foams are widely used polymer phase with voids and an additional solid as insulating and core materials for furniture, or hollow phase distributed throughout the cooling and freezing systems, in house building, polymer, while Foams or cellular materials are ship building, piping, tanks, etc.[1,2]. The use of materials that have a regular arrangement of cells rigid foams is a result of their low heat conduction and solid struts. Thus, the term composite foam coefficient, low density, low water absorption and excludes conventional, single-phase foams made relatively good mechanical strength [3]. The PU by expanding polymers such as (polystyrene, foams have been applied also as core materials of polyurethane, or polypropylene), also excluded sandwich constructions with steel plates, in are structures with single-phase core materials building the industrial houses carrying freezers and covered with a solid skin because the second and cold stores, where they have to fulfill both phase, the skin, is not dispersed throughout the insulating and mechanical requirements. In polymer phase [14]. addition, polyurethane products, for the most part, Composite foams can be classified as follows: are self-supporting, which makes them useful as syntactic foam, particle reinforced foam and fiber- construction insulation panels and as structural reinforced foam. The additional solid components elements in construction applications [3, 4]. PU are combined to enhance certain properties

NUCEJ Vol.18 No.1. 2015 Marhoon, Rasheed pp.41 - 49 important to the function of the composite foam Thereafter, part-B (MDI) was added to the part such as strength, stiffness, electrical or mixture and mixed at a similar speed for another thermal conductivity [14, 15]. 15 sec. and the mixture was left to produce expanded foam. All composite foams were cured 2. Objective at ambient temperature (25◦C) for 72 hr., and Polyurethane foam is very talented rigid glass wool was added based on weight percentage polymer foam for shock, acoustic and thermal of the overall weight of polyol and MDI resin insulating applications, but it has limitations (w/w %) which were (2, 4, 6, 8,10) %wt. as which exclude its application as a single material. shown in Figure (2). Polyurethane properties are modified by controlling the stages of syntheses or by using 3.3 Foam Composites Measurement fibrous reinforcement additives to overcome some Methods of these limitations. For example, one of the main The specimens were cut according to the limitations of rigid PU foams comes from their standard dimensions for each test. An average of reduced mechanical properties in the case of three different determinations was obtained for all sandwich structures, increasing the risk of experiments except for hardness test, where five possible core crushing, shear or debonding readings were taken from different places of one from the surface skins. The aim of the present sample. The mechanical properties of the foams work is the synthesis of rigid polyurethane foams were conducted parallel to foam rise direction. (PU) modified with short glass fibers in the form Flexure tests are performed with 2.5 kN load at a of (glass wool). The effects of glass wool speed of 2 mm/min. The tests were performed insulation on the foams have been analyzed in according to ASTM D 790-03 [18]. Compression terms of density, thermal conductivity, water strength was determined according to ASTM absorption, mechanical properties (impact, D1621-00 [19]. Impact test was performed compression and flexural ). according to ASTM D4812-99 for unnotched Izod impact test [20]. Density of the foam was 3. Experimental measured according to ASTM D1622-03 [21]. 3.1 Materials Hardness test was performed by using Shore hardness (D) and according to ASTM F1957–99 A two-component polyurethane foam (PU) [22]. Water Absorption test was performed system specifically formulated for the preparation according to ASTM D570-98 [23]. Thermal of medium–high density rigid PU foams ® conductivity was measured using Lee's Disk with (POLYFOAM 55 ) was produced by sample dimensions of 40 mm diameter and 5 mm (POLYBIT), where part-A is a mixture of polyol, thickness. The instrument consists of a heating blowing and curing agents, catalysts and coil and three brass disks. The specimen was stabilizers, with a viscosity of 900 cps at 20 ◦C 3 secured between the brass disks (1, 2) and the and a density of 1.14 g/cm , and part-B is a heating coil was fixed between the brass disks (2, modified diphenylmethane-diisocyanate (MDI), 3). The applied voltage across the terminal of the with a viscosity of 200 cps at 25 ◦C and a density 3 heating coil is 6 V. and the current is 0.2 A. A of 1.24 g/cm . Both components are liquid at heating heater was used to heat the three brass room temperature [16]. Glass wool (URSA ® disks (1, 2, 3) and heat transfer was through the GLASSWOOL ) insulation was produced by specimen from the bass disk (2) to brass disk (1). URSA Uralita group –Turkey, have a density of 3 The temperature of the disks increases gradually 16 kg/m and an individual fiber diameter until it reaches the equilibrium temperature of all between 6.1- 7.7 μm [17]. disks.

3.2 Composite Foam Preparation 4. Results and Discussion

Rigid PU-based foams were prepared by 4.1 Physical Properties mixing equal amount 1:1 of part-A (polyol) and 4.1.1 Water Absorption part B (isocyanate (MDI)) components for 15 s Figure (3) show the relationship between water and pouring in a wooden mould (60×90×195 mm) absorption percentage and weight fraction of the as shown in Figure (1). The mould was closed glass wool filler, which were added to the rigid with a lid and the mixture was allowed for PU’s polyurethane foam. Water absorption behavior of synchronized polymerization and foaming. Rigid polymer filled composites at a particular PU reinforced composite foams were prepared by environmental condition is determined by many forming in place method by initially pre-mixing factors, such as processing techniques, matrix glass wool insulation (were dried for 24 hr. at ◦ filler characteristics, composition of the 100 C) with the polyol prior to pouring into the composites, and duration of immersion in water mold with hand mixing for 1 min. after the [24]. The results had revealed that the water mixture was allowed to degas for 2 min. into a absorption percentage increases with increasing wooden mould lined with aluminum foil.

NUCEJ Vol.18 No.1. 2015 Marhoon, Rasheed pp.41 - 49 weight fraction of (glass wool) in another term the Figure (6). However the thermal conductivity of hygroscopicity of polyurethane / glass wool foam rigid polyurethane foam composite changes a composites increases as glass wool content little in the fiberglass wool weight fraction range increases, and reaches 41.17% at 10 wt.% as 2 to 10 %wt. compared to water absorption percentage of 4.2 Mechanical Properties (4.785%) for rigid polyurethane foam. This increase may be due to the glass wool fiber filler 4.2.1 Hardness which have a higher water absorption percentage The reinforcement of rigid polyurethane foams than the matrix material; fiber glass wool has with glass wool has a great role in obtaining a moisture absorption of 3% of weight at a relative higher hardness. A shore D hardness test was used humidity of about 90% [17]. In addition, for specimen of rigid polyurethane before and reinforced samples have many channels which after reinforcing with glass wool. Figure (7) assist water to penetrate inside the sample. The shows the effect of glass wool weight fraction on presence of interfaces between the matrix and the hardness. It can be seen that the hardness of short glass wool fibers are considered as capillary polyurethane foams increases with increasing the tubes for water transport and penetration inside fiber glass wool weight fraction. Results have the samples. shown that the hardness of solid polyurethane foams is (71.46 shore D) and reaches (83.85 shore 4.1.2 Density D) at weight fraction of (8%). Hardness is

Figure (4) shows the variation in density of commonly defined as a resistance of material to polyurethane foam at different wt.% of wool local deformation. The increase in %wt. glass glass. From this figure, it is clearly seen that the wool fibers content leads to an increase in the density increases with increasing % wt. of glass hardness due to the increase in material resistance wool. The density of solid polyurethane foam is against the plastic deformation. In other words, (61.24 Kg/m3) and reaches (119.44 Kg/m3) at a the addition of the glass wool leads to a decrease weight fraction of (10 %wt.). This increase can be in the elasticity and an increase in the rigid related to both the polyol-isocyanate exothermic polyurethane foams matrix surface resistance to the indentation. reactions where carbon dioxide was generated from the reaction. Due to the release of heat from 4.2.2 Compression Strength the exothermic reactions, the carbon dioxide Figure (8) illustrates the compression strength bubbles grew (small size cell with spherical and of rigid polyurethane foam base matrix composite polyhedral shape) and expanded the polymerizing filled with different weight fraction of glass wool. polymer to form a foam volume [5]. When adding Results have revealed that compression strength glass wool to polyurethane foam, bubble rise and has increased with the addition of glass wool to growth are physically hindered by the presence of polyurethane foam and the values were (264.77, glass wool fibers and also cell size generally 294.19, 343.23, 411.87 and 441.29) kPa at (2, 4, decreases as the glass wool %wt. content 6, 8 and 10) %wt. glass wool respectively. The increases indicating that cell growth is hindered compression strength of pure rigid polyurethane by the fibers. In addition, the closed cell content foam is (235.35 kPa). The increase of strength of decreases with the glass wool fibers %wt. content, the composite is due to the addition of higher and that will lead to density increase of strength and stiffness glass wool fibers. In polyurethane composite. addition, the decrease of cell size may also have 4.1.3 Thermal Conductivity an effect on the mechanical strengthening of the composite. Figure (5) shows the relationship between the thermal conductivity with different values of 4.2.3.1 Flexural Strength weight fraction of wool glass. Thermal conductivity (k) is the most important property of Figure (9) show the relationship between foam for insulation application. The overall flexural strength and weight fraction for the thermal conductivity of foam increases with composite of polyurethane foam reinforced by increasing the %wt. wool glass content. Thermal glass wool. That flexural strength of the prepared conductivity of solid polyurethane foam is foam composite material increases with an (0.0290W/m.°C) and reaches (0.0391W/m.°C) at a increase in the weight fraction up to 8 %wt., then weight fraction of (10 %wt.). The overall thermal the strength decreases. The reason behind such conductivity of the composite foams is increased behavior is that short- fibers of glass wool are due to the high thermal conductivity of glass wool able to increase the flexural strength of the fibers, and also when the reduction in cell size is polyurethane foam since they offer appropriate accompanied by a noteworthy density increase, fiber-matrix adhesion so as to resist deformation. thus thermal conductivity practically increases as The effect of fiberglass wool on flexural strength a result of the cell size reduction as shown in may be also due to the increase in the short fiber glass content in a polyurethane foam composite

NUCEJ Vol.18 No.1. 2015 Marhoon, Rasheed pp.41 - 49 and that in turn lead to an increase in effective improved compared to that of pure polyurethane surface fracture energy. The dispersed short fibers foam and so the foam composites have higher glass wool enhances the plastic deformation, toughness to withstand the sudden loads make the crack propagation path longer, and compared to that of the pure foam. absorb a portion of energy. Hence, the surface fracture energy increases and the flexural strength 5. Conclusions of composites increase with weight fraction The main conclusions of this study on rigid percentage of glass wool. After (8% wt. glass polyurethane matrix foam composites are as wool), the flexural strength decreases with further follows. additional increase. This may be related to an 1. It was found that increasing the glass wool increase in the viscosity (during mixing) of the content within the rigid polyurethane foam matrix at large additions of glass wool causing matrix results in significant increase in the difficulty in matrix fluidity and reduced ability to thermal conductivity. Therefore, it is not penetration between fibers which reduces fiber recommend to add glass wool for wetting prior to hardening of the matrix causing a polyurethane foam for thermal insulation decrease in adhesion (weaker interface) between purposes. the matrix and the fibers, and as a result crack propagation will occur. 2. The properties of the rigid polyurethane foam-glass wool composites are 4.2.3.2 Flexural Modulus significantly improved by varying the

Results of flexural modulus of polyurethane amount of glass wool. It was found that foam before and after the addition of fiber glass increasing the glass wool content within the wool have revealed that flexural modulus matrix material, resulted in significant increases with the increase in weight fraction as improvement in mechanical properties like shown in Figure (10). Flexural modulus of pure hardness, flexural strength, compressive rigid polyurethane foam is (9.227 MPa.) and strength, impact strength at the cost of increases with increasing weight fraction until it increased density. reaches a value of (28.04 MPa.) at a weight 3. Peak values of mechanical properties like fraction of (10%). This observation highlights the hardness, flexural strength were found at 8 fact that the incorporation of glass wool into wt.% glass wool and compressive strength, polyurethane foam matrix improves the stiffness flexural modules, impact strength were of the latter because stress is transferred from the found at 10 wt.% glass wool. matrix to the fiber resulting in stronger foam composites. The result attained in this study is in References agreement with the findings of Kim et. al. [2]. [1]. Randall D., Lee S., The Polyurethanes Book, Wiley, New York, 2002. 4.2.4 Impact Strength [2]. S. H. Kim, H. C. Park, H. M. Jeong, B. K.

The addition of the fiber glass wool to the Kim, Glass fiber reinforced rigid polyurethane foam enhanced significantly the polyurethane foams, Journal of Materials impact strength as shown in Figure (11). The Science, Vol. 45, Issue 10, pp. 2675-2680, reason for impact strength improvement may be May 2010. IVSL. due to the increase in fracture surface area which [3]. Wit Witkiewicz, Andrzej Zieliński, results from unregular path of crack due to short PROPERTIES OF THE POLYURETHANE fibers which act as traverse in front of crack (PU) LIGHT FOAMS; ADVANCES IN propagation. Hence, the surface fracture energy MATERIALS SCIENCE, Vol. 6, No. 2 (10), increases and the impact strength of composites October 2006. increase with %wt. of glass wool. Another reason [4]. Herman F. Mark, Encyclopedia of Polymer might be the plastic deformation (plastic zone) Science and Technology: that results from the short fibers, around the POLYURETHANES, Third Edition, Vol. 4, crack. That plastic zone would have to support John Wiley & Sons, 2005. part of the load in order to reduce stresses at the [5]. David Eaves, Handbook of Polymer crack tip, and hence prevent fracture from Foams, Rigid polyurethane foams, Rapra occurring at low values of the applied load. In Technology Limited, Shawbury, UK, 2004. effect, the plastic zone that surrounds the crack tip [6]. Arthur H. Landrock, Handbook of Plastic acts as (crack tip shielding), because it applies a Foams Types, Properties, Manufacture and compressive force to the crack surfaces and closes Applications.: Thermosetting Foam; 1st the crack tip and as a result causes retardation of edition. Noyes Publications. pp. 40-78. 1995. crack growth. IVSL. This indicates that as the content of short fibers of [7]. M.C. Silva, J.A. Takahashi, D. Chaussy, glass wool increases, the impact strength is M.N. Belgacem, G.G. Silva, Composites of rigid polyurethane foam and cellulose