polymers Article
The Abrasive Wear Resistance of the Segmented Linear Polyurethane Elastomers Based on a Variety of Polyols as Soft Segments Konrad Kwiatkowski 1, * and Małgorzata Nachman 2 1 2
*
Department of Mechanics and Machine Design Fundamentals, West Pomeranian University of Technology Szczecin, Al. Piastów 19, 70-310 Szczecin, Poland Institute of Materials Science and Engineering, West Pomeranian University of Technology Szczecin, Al. Piastów 19, 70-310 Szczecin, Poland;
[email protected] Correspondence:
[email protected]; Tel.: +48-506-017-681
Received: 19 November 2017; Accepted: 6 December 2017; Published: 12 December 2017
Abstract: The presented results make an original contribution to the development of knowledge on the prediction and/or modeling of the abrasive wear properties of polyurethanes. A series of segmented linear polyurethane elastomers (PUR)—In which the hard segments consist of 4,40 -methylene bis(phenylisocyanate) and 1,4-butanodiol, whilst polyether, polycarbonate, or polyester polyols constitute the soft segments—Were synthesized and characterized. The hardness and wear performance as functions of the variable chemical composition of polyurethane elastomers were evaluated in order to define the relationship between studied factors. The microstructure was characterized in detail, including analysis of the hydrogen bonding by Fourier transformed infrared (FT-IR) spectroscopy and the phase structure by X-ray scattering (WAXS) and differential scanning calorimetry (DSC) methods. The presented studies provide the key features of the polymer composition affecting the abrasive resistance as well as attempts to explain the origin of the differences in the polyurethane elastomers’ performance. Keywords: polyurethane elastomers; PUR; abrasive wear; microstructure
1. Introduction The literature data state quite clearly that, on the basis of the specific mechanical properties of the materials, it is possible to predict the performance and durability of the final product; however, there is an exception—The determination of the wear properties in friction pairs [1–7]. The huge number of the possible variants of friction pairs and the operating features have not yet allowed the creation of an effective recipe for the prediction of the wear intensity of the friction elements. The prediction and/or modeling of the wear properties of the synthetic materials, especially polyurethane elastomers (PUR), is particularly difficult, mostly due to the wide variation in their properties [8–13]. The use of various raw materials, variable chemical composition, or application of different production methods and further processing methods gives a chance to produce PUR with widely varied properties. In general, the overall mechanical properties of PUR can be quite easily tailored by the thought-out selection of the components, composition, and preparation conditions [14–17]. For example: The hardness of the final product mainly depends on the content of the hard segments (HS) in the polyurethane. The hardness of the material is higher when the content of the HS is higher. However, in the literature there is a lack of data which could facilitate the prediction and/or modeling of the wear properties of PUR. This extensive research problem is very essential, mainly due to the fact that PUR offer an outstanding abrasive wear resistance when compared with rubbers, plastics, or even metals, and are therefore widely used in the tribological systems where a high
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abrasion resistance is required. For example: conveyor belt cleaning systems (PU scrapers), vibrating screens (PU sieves), or wheels for heavy duty vehicles, but also in the most severe applications of the aerospace and military industries, and so on [14,16]. Wear and friction are much better understood for metals than they are for polymers. Therefore, researchers try to make direct applications of metal friction and wear to polymers [6,7,10,18]. Applying the results from the wear of metals to polymers suggested that abrasive wear should be related to the hardness [10]. Therefore, the users of PUR are convinced that there is a relationship between the hardness and the abrasion resistance, or, more precisely, if the material has higher hardness, then it is more resistant to abrasive wear. Unfortunately, the literature data do not quite clearly specify this dependency. Zygmunt Wirpsza in his scientific work [14], confirmed the validity of the relationship quoted above. However, the results obtained in the other abrasion characteristics studies [19–22] demonstrate a completely different relationship—The abrasive wear resistance of PUR increases along with the content of soft segments (SS), i.e., the elastomers with lower hardness were more resistant to abrasive wear. Nevertheless, the results obtained in our preliminary study [23] showed that the polyurethane elastomers, despite having the same hardness, can differ significantly in their abrasion resistance. It has been shown that the differences in the abrasive wear are substantial (up to 20 times more for materials with the same hardness). The differences in the abrasion resistance are most likely caused by the various components used in the preparation of the final product. This means that the most important factor in the wear resistance of PUR is not their macroscopic hardness but the chemical structure and the resulting morphology. The segmented chemical structural composition of PUR is the specific structural feature which strongly influences their properties [14–17]. The molecular structure of PUR is quite complicated. They phase separate during the polymerization reaction, forming a supermolecular structure [24–27]. Moreover, structural units of various forms and sizes develop during the reaction [28–30]. In this study, the microphase-separated structure is analyzed. The polyurethane chain is composed of the HS and the SS. In most of the polyurethanes, the phase segregation occurs due to the incompatibility (different polarity and chemical nature) between these segments. The SS are composed of polyols which may differ in chemical structure, molecular weight, or functionality. The HS are obtained from isocyanates and low-molecular-weight chain extenders. Practically, only a few isocyanates are used, with 4,4-diphenylmethane diisocyanate (MDI) and toluene diisocyanate (TDI) used most frequently [31]; therefore, it is most likely the chemical structure of the SS that is the most important factor influencing the abrasive wear resistance of the polyurethane elastomers. Although the effect of the chemical structure of the components on the mechanical properties of the polyurethane elastomers has been investigated extensively [32–35], the effect of the chemical composition and the resulting physical structure on the abrasive wear resistance has not yet been well described [8–10,19]. In this study, a range of segmented linear polyurethane elastomers were synthesized with polyether, polycarbonate, and polyester polyols as soft segments. All polyols were characterized by the molecular weight of 2000 g/mol. The HS consisted of 4,40 -methylene bis (phenylisocyanate) (MDI) and 1,4-butanodiol (1,4-BD). The stoichiometric ratio of the isocyanate and hydroxyl groups (NCO/OH ratio) was kept constant. The series of polyurethane elastomers based on the polyether polyol were synthesized with different concentrations of the polyether soft segments in order to assess the relationship between the hardness and the abrasive wear resistance. Additionally, one series of the samples was prepared using a diamine chain extender. The obtained materials were analyzed for the density, hardness, and abrasive wear resistance. The morphology was characterized by wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and by Fourier transformed infrared (FT-IR) spectroscopy, the latter being one of the main methods used to describe phase separation in PUR [36–40]. The differences in the chemical
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structure resulted in the varied physical structure of the polyurethane elastomers and, therefore, Polymers 2017, 9, 705 3 of 13 in strongly affected wear properties.
2. Materials and Experimental Methods 2. Materials and Experimental Methods 2.1. Materials 2.1. Materials and and Synthesis Synthesis The series series of of the the segmented segmented linear linear PUR PUR were were synthesized synthesized using using aa two-step two-step polymerization polymerization The method, following the same procedure and conditions as described previously [21]. The first stage stage of of method, following the same procedure and conditions as described previously [21]. The first the synthesis synthesis involved involved the thepreparation preparationofofaaprepolymer prepolymerby bymixing mixingpolyol polyoland and isocyanate (with 6 wt the isocyanate (with 6 wt % % excess) to produce an isocyanate-terminated molecule. In the second stage, a diol or diamine chain excess) to produce an isocyanate-terminated molecule. In the second stage, a diol or diamine chain extender was was added added to to the the prepolymer. prepolymer.Consequently, Consequently,the thepolymerization polymerizationtakes takesplace, place,and andproduces producesa extender a multi-block copolymer. A schematic representation of the reaction and the synthesis process using multi-block copolymer. A schematic representation of the reaction and the synthesis process using a a two-step polymerization method is shown in Figure 1. two-step polymerization method is shown in Figure 1.
Figure Schematic representation representation of of the the synthesis synthesis process process and and the the reaction reaction using using aa two-step Figure 1. 1. Schematic two-step polymerization polymerization method. method.
different linear polyols withwith various chemical structures were used: As the the soft softsegments, segments,three three different linear polyols various chemical structures were ® ®2000, DuPont, the polyether polyol, which waswas poly(tetramethylene-oxide) (PTMO used: the polyether polyol, which poly(tetramethylene-oxide) (PTMOTerathane Terathane 2000, DuPont, ® C 2200, ®Bayer, Wilmington,DE, Delaware, USA); the polycarbonate polyol (Desmophen C 2200, Bayer, Leverkusen, Wilmington, USA); the polycarbonate polyol (Desmophen Leverkusen, Germany); Germany); and thepolyol, polyester polyol, based on polyethylene (Polios 60/20, and the polyester based on polyethylene glycol and glycol adipic and acidadipic (Poliosacid 60/20, Purinova, Purinova, Bydgoszcz, All polyols were characterized by the molecular Bydgoszcz, Poland). AllPoland). polyols were characterized by the molecular weight of 2000 weight g/mol. of The2000 HS 0 g/mol. TheofHS of bis 4,4′-methylene bis (phenylisocyanate) (MDI, Sigma-Aldrich, St. Louis, consisted 4,4 consisted -methylene (phenylisocyanate) (MDI, Sigma-Aldrich, St. Louis, MO, USA) and Missouri, USA) and 1,4-butanodiol (BD, Wilmington, Delaware, USA). series of 1,4-butanodiol (BD, DuPont, Wilmington, DE, DuPont, USA). A series of poly(ether-urethane)s wasA synthesized poly(ether-urethane)s was synthesized with different concentrations polyether SS: 55, 60, with different concentrations of the polyether SS: 50, 55, 60, 65, 70 wt of %.the Additionally, one50, series of 0 65, samples 70 wt %. one serieschain of the samples was prepared using diamine chain the wasAdditionally, prepared using diamine extender—4,4 -methylenebis(2-chlorobenzenamine) extender—4,4′-methylenebis(2-chlorobenzenamine) (MOCA, Sigma-Aldrich, St. Louis, MO, USA). (MOCA, Sigma-Aldrich, St. Louis, MO, USA). The molecular structures and detailed specifications The molecular structures and detailed specifications of the raw materials are provided Table 1. of the raw materials are provided in Table 1. The stoichiometric ratio of the isocyanate andinhydroxyl The stoichiometric ratiowas of kept the constant—1.05 isocyanate andin all hydroxyl groups (NCO/OH ratio) was kept groups (NCO/OH ratio) materials. constant—1.05 in all materials. The synthesized materials were placed into a mould and left to cure at room temperature for ◦ C for synthesized materials werewere placed into at a mould left2 to cure at room temperature for 24 24 h. The Prior to annealing, all samples heated 60 ± 5 and h in order to complete the reaction. h. Prior to annealing, all samples at 60 ± 5 °C h 5in◦order complete thecooled reaction. The annealing was conducted for were 2 h atheated the temperature offor 1002 ± C. Thetosamples were to The annealing was and conducted for 2 h the weeks temperature ± 5 The °C. The samples were cooled to room temperature conditioned forattwo before of the100 tests. compositions, the reactants’ room temperature conditioned for two weeks before theintests. molar ratio, and theand hardness of the prepared PUR are listed TableThe 2. compositions, the reactants’ molar ratio, and the hardness of the prepared PUR are listed in Table 2.
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Polymers 2017,1.9,Molecular 705 Table structure and detailed specifications of the raw materials used for the synthesis. 4 of 13 Polymers 2017, 9, Molecular 705 of 13 4 of 13 structure and detailed specifications of the raw materials used for the synthesis.44 of Polymers 2017, 9,Table 705 Polymers 2017, 1. 9, 705 13 Molecular Hydroxyl Melting Table 1. Molecular structure and detailed specifications of the raw materials used for the synthesis. Molecular Hydroxyl Melting Raw materials Molecular structure weight, value, temperature, Table 1. Molecular structure and detailed specifications of the raw materials used for the synthesis. Table 1. Molecular structure and detailed specifications of the raw materials used for the synthesis. Raw materials Molecular structure weight, value, temperature, Molecular Hydroxyl Melting g/mol mg KOH/g °C Table 1.materials Molecular structure and detailed specifications Molecular ofweight, the raw materials used for the synthesis. Molecular Hydroxyl Melting g/mol mg KOH/g °C Raw Molecular structure value, temperature, Polyether, Hydroxyl Melting Raw materials Molecular structure weight, value, temperature, ® g/mol mg KOH/g °C Polyether, 2000 53.4–59.1 28–40 Terathane Raw materials Molecular structure weight, value, temperature, g/mol mg KOH/g °C ® Molecular Hydroxyl 2000 53.4–59.1 28–40 Terathane Polyether, (PTMO) g/mol mg KOH/gvalue, °CMelting Raw2000 materials Molecular structure ◦C Polyether, ® weight, g/mol mg KOH/g temperature, 2000 (PTMO) 2000 53.4–59.1 28–40 Terathane Polyether, Polycarbonate, ® 2000 53.4–59.1 28–40 Terathane ®®® 2000 (PTMO) 2000 53.4–59.1 28–40 Terathane Polycarbonate, 53–59 39–52 Desmophen Polyether, Terathane H O CH 2 CH 2 CH 2 CH2 OH 2000 (PTMO)® 2000 53.4–59.1 28–40 2000 2000 53–59 39–52 Desmophen Polycarbonate, 2000 (PTMO) C (PTMO) 2200 n Polycarbonate, ® C 2200 2000 53–59 39–52 Desmophen Polycarbonate, ® Polycarbonate, 2000 53–59 39–52 Desmophen Polyester, C®2200 ® 2000 53–59 2000 53–59 39–5239–52 Desmophen 2000 54–58 40–53 Desmophen C60/20 2200 C 2200 Polyester, Polios C 2200 2000 54–58 40–53 Polios 60/20 Polyester, 2000 54–58 40–53 Polyester, Polios Polyester, Polyester, Polios60/20 60/20 2000 54–58 40–53 2000 54–58 40–53 Diisocyanate, 2000 54–58 40–53 Polios 60/20 250 38–42 Polios 60/20 Diisocyanate, 4,4′-MDI 250 38–42 4,4′-MDI Diisocyanate, 250 - 38–42 Diisocyanate, 4,40 -MDI 250 38–42 Diisocyanate, 4,4′-MDI Diisocyanate, 250 38–42 1,4-butanodiol, 250 -38–42 4,4′-MDI 90 20.4 4,4′-MDI 1,4-butanodiol, BD 90 - 20.4 20.4 1,4-butanodiol, BD 90 BD 1,4-butanodiol, 90 20.4 1,4-butanodiol, BD 1,4-butanodiol, Diamine, 90 20.4 90 20.4 267 - 102–107 BD Diamine, MOCA 267 102–107 Diamine, BD MOCA 267 102–107 MOCA Diamine, 267 102–107 Diamine, MOCA Diamine, 267 102–107 267 102–107 MOCA Table 2. Summary of the prepared polyurethane elastomers’ (PUR) chemical composition and Table 2.MOCA Summary of the prepared polyurethane elastomers’ (PUR) chemical composition and hardness, Table 2. and Summary of the molar prepared polyurethane elastomers’ (PUR) chemical composition and hardness, the reactants’ ratio. and the reactants’ molar ratio. Table 2. Summary of the prepared polyurethane elastomers’ (PUR) chemical composition and hardness, and the reactants’ molar ratio. Molar ratio: Table 2. Summary of the prepared polyurethane elastomers’ (PUR) chemical composition and hardness, and the reactants’ molar ratio. Table 2. Summary of the prepared polyurethane elastomers’ (PUR) chemical and Softcomposition segment Hardness, Molar ratio: Materialsand the reactants’Composition polyol/MDI/chain hardness, molar ratio. Molar ratio: Soft segment Hardness, hardness, and the reactants’ molar ratio. (SS), wt % ShD Soft segment Hardness, Materials Composition polyol/MDI/chain Molar ratio: extender Materials Composition polyol/MDI/chain (SS), wt % ShD Soft segment Hardness, Molar ratio: (SS), wt % ShD extender Materials Composition polyol/MDI/chain PUR_50/Ether/BD PTMO, BD, MDI 1.00/6.45/5.15 50 52 Molar ratio: Soft segment Hardness, extender (SS), wt % ShD Soft segment Hardness, Materials Composition polyol/MDI/chain extender PUR_50/Ether/BD PTMO, BD, MDI MDI 1.00/6.45/5.15 50 52 PUR_55/Ether/BD PTMO, BD, 1.00/5.33/4.08 55 47 Materials Composition polyol/MDI/chain (SS), wt % ShD (SS), wt % ShD PUR_50/Ether/BD PTMO, BD, MDI 1.00/6.45/5.15 5050 52 extender PUR_55/Ether/BD PTMO, BD, BD, MDI MDI 1.00/5.33/4.08 55 47 PUR_50/Ether/BD 1.00/6.45/5.15 52 PUR_60/Ether/BD PTMO, 1.00/4.40/3.19 60 43 extender PUR_55/Ether/BD PTMO, BD, MDI 1.00/5.33/4.08 5550 47 PUR_50/Ether/BD PTMO, MDI 1.00/6.45/5.15 52 PUR_60/Ether/BD PTMO, BD, MDI 1.00/4.40/3.19 60 43 PUR_55/Ether/BD 1.00/5.33/4.08 55 47 PUR_65/Ether/BD PTMO, BD, MDI 1.00/3.60/2.43 65 38 PUR_50/Ether/BD 1.00/6.45/5.15 50 52 PUR_60/Ether/BD PTMO, BD, MDI 1.00/4.40/3.19 6055 43 PUR_55/Ether/BD PTMO, BD, MDI 1.00/5.33/4.08 47 PUR_65/Ether/BD PTMO, BD, BD, MDI MDI 1.00/3.60/2.43 65 38 PUR_60/Ether/BD 1.00/4.40/3.19 60 43 PUR_70/Ether/BD PTMO, 1.00/2.93/1.79 70 30 PUR_55/Ether/BD 1.00/5.33/4.08 47 PUR_65/Ether/BD PTMO, BD, MDI 1.00/3.60/2.43 6555 38 PUR_60/Ether/BD PTMO, BD, MDI 1.00/4.40/3.19 60 43 PUR_70/Ether/BD 1.00/2.93/1.79 70 30 PUR_65/Ether/BD PTMO, BD, MDI 1.00/3.60/2.43 65 38 PUR_70/Carbonate/BD Desmophen 2000, BD, MDI 1.00/2.93/1.79 70 37 PUR_60/Ether/BD 1.00/4.40/3.19 43 PUR_70/Ether/BD PTMO, BD, MDI 1.00/2.93/1.79 7060 30 PUR_65/Ether/BD PTMO, BD, MDI 1.00/3.60/2.43 65 38 PUR_70/Carbonate/BD Desmophen 2000, BD, MDI 1.00/2.93/1.79 70 37 PUR_70/Ether/BD 30 PUR_70/Ester/BD Polios 60/20, MDI 1.00/2.93/1.79 70 32 PUR_65/Ether/BD PTMO, BD,BD, MDI 1.00/3.60/2.43 38 PUR_70/Carbonate/BD Desmophen 2000, BD, MDI 1.00/2.93/1.79 7065 37 PUR_70/Ether/BD PTMO, BD, MDI 1.00/2.93/1.79 70 30 PUR_70/Ester/BD Polios 60/20, BD, MDI 1.00/2.93/1.79 70 32 PUR_70/Carbonate/BD Desmophen 2000, BD, MDI 37 PUR_70/Ester/MOCA Polios 60/20, MOCA, MDI 1.00/2.28/1.17 32 PUR_70/Ether/BD PTMO, BD, MDI 1.00/2.93/1.79 30 PUR_70/Ester/BD Polios 60/20, BD, MDI 1.00/2.93/1.79 7070 32 PUR_70/Carbonate/BD Desmophen 2000, BD, MDI 1.00/2.93/1.79 70 37 PUR_70/Ester/MOCA Polios 60/20, MOCA, MDI 1.00/2.28/1.17 PUR_70/Ester/BD Polios 60/20, BD, MDI 1.00/2.93/1.79 70 32 PUR_70/Carbonate/BD Desmophen 2000, BD, MDI 37 PUR_70/Ester/MOCA Polios 60/20, MOCA, MDI 1.00/2.28/1.17 70 32 PUR_70/Ester/BD Polios 60/20, BD, MDI 1.00/2.93/1.79 70 32 PUR_70/Ester/MOCA Polios 60/20, MOCA, MDI 1.00/2.28/1.17 PUR_70/Ester/BD Polios 60/20, BD, MDI 1.00/2.93/1.79 70 32 2.2. Methods PUR_70/Ester/MOCA Polios 60/20, MOCA, MDI 1.00/2.28/1.17 70 32 PUR_70/Ester/MOCA Polios 60/20, MOCA, MDI 1.00/2.28/1.17 70 32 2.2. Methods
2.2. Methods 2.2. Methods 2.2.1. The Abrasion Resistance
2.2. Methods 2.2.1. The Abrasion Resistance 2.2. Methods The resistance 2.2.1. The abrasion Abrasion Resistanceof the test samples against mechanical action upon a surface was 2.2.1. The Abrasion Resistance abrasion resistance of the cylindrical test samples against mechanical action upon a surface 2.2.1.The The by Abrasion Resistance assessed employing a rotating roller device (Figure 2) in accordance with was ISO 2.2.1. The Abrasion Resistance The abrasion resistance of the test samples against mechanical action upon a surface was assessed by employing a rotating cylindrical roller device (Figure 2) in accordance ISO standards. The elastomer test specimen hadmechanical a cylindricalaction form, 16 ± 0.2amm in with diameter The4649:2002 abrasion resistance of the test samples against upon surface was assessed The abrasion resistance of the cylindrical test samples against mechanical action upon a surface was assessed by employing aelastomer rotating roller device (Figure 2) in accordance with ISO The abrasion resistance of the testspecimen samples against mechanical action a surface was 4649:2002 standards. The test had a cylindrical form, 16the ±upon 0.2 mm inroller. diameter and 2 mm in height. It was fixed to slide over the abrasive sheet attached to rotating The by employing a rotating cylindrical roller device (Figure 2) in accordance with ISO 4649:2002 standards. assessed by employing a rotating test cylindrical roller device (Figure 2) in accordance with ISO 4649:2002 standards. The specimen hadsheet a cylindrical form, 16the ±was 0.2 mm± in diameter assessed by aelastomer rotating cylindrical roller device (Figure 2) to in accordance with ISO and 2 mm in employing height. fixed to slide over the abrasive sheet attached rotating roller. The sliding distance was It 40was m and the sample-abrasive contact pressure 10 0.2 N. The 4649:2002 standards. The elastomer test specimen had a cylindrical form, 16 ± 0.2 mm in diameter The elastomer test specimen had a cylindrical form, 16 ± 0.2 mm in diameter and 2 mm in height. and 2 mm in height. It was fixed to slide over thevolume abrasive sheet attached to rotating roller. 4649:2002 standards. The elastomer test hadsheet a cylindrical form, 16the ±was 0.2 diameter sliding distance was 40 m and the sample-abrasive contact pressure 10 N. The abrasion resistance was determined as a specimen relative loss of the test sample ( Δmm )0.2 compared V rel± in and 2tomm in height. It40 was fixed tosheet slide over the abrasive sheet attached to the rotating roller. The was It was fixed slide over the abrasive attached to the rotating roller. The sliding distance sliding distance was m and the sample-abrasive sheet contact pressure was 10 ± 0.2 N. and 2 mm in height. It was fixed to slide over the abrasive sheet attached to the rotating roller. The abrasion resistance was determined as a relative volume loss of the test sample ( Δ V rel ) compared with thedistance abrasivewas sheet40calibrated using a standard reference. As the pressure standard was reference, the N. rubber sliding m and the sample-abrasive sheet contact 10 ± 0.2 The sliding distance was 40calibrated msheet and the sample-abrasive sheet contact N. The was abrasion resistance was determined as a relative volume loss of±the test ( Δ10 compared 40 m and thethe sample-abrasive contact pressure was 10 0.2pressure N.sample Thewas abrasion resistance V rel± )0.2 with abrasive sheet using standard reference. the standard reference, the rubber compound No. 1 from Institute Materials Research Testing (Berlin, was abrasion resistance wasFederal determined as aafor relative volume loss As ofand the test sample ( Δ VGermany) ) compared rel ) compared abrasion resistance was determined as the aafor relative volume loss of the test sample ( Δ VGermany) determined as relative volume loss of test sample (∆VAs )the compared with thethe abrasive with the aabrasive sheet calibrated using standard reference. standard reference, rubber rel compound No. 1 from Federal Institute Materials Research Testing (Berlin, was sheet reland used. with the abrasive sheet calibrated using a standard reference. As the standard reference, the rubber compound 1 sheet from Federal Institute Materials Research Testing (Berlin, Germany) was 1 from with the abrasive calibrated using afor standard reference. Asand thethe standard reference, the rubber used. calibrated using aNo. standard reference. As the standard reference, rubber compound No. compound No. 1 from Federal Institute for Materials Research and Testing (Berlin, Germany) was used. compound No.Materials 1 from Federal Institute Materials Research and Testing Federal Institute for Research andfor Testing (Berlin, Germany) was(Berlin, used. Germany) was used. used.
The abrasive sheet was made of aluminum oxide with a grain size of 60, and it was calibrated to a standard reference compound mass loss of between 180 and 200 mg for an abrasion distance of 40 m. The preparation of the abrasive sheet and its calibration using a standard reference compound was a very important part of the method.
1
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FigureFigure 2. Schematic illustration of (a)ofthe sliding overover the abrasive sheetsheet and and (b) the 2. Schematic illustration (a)test thesample test sample sliding the abrasive (b) rotating the cylindrical roller device.roller device. rotating cylindrical
The abrasive sheet was made of aluminum oxide with a grain size of 60, and it was calibrated to
After the abrasion test, the mass loss of the specimen was determined and its volume was a standard reference compound mass loss of between 180 and 200 mg for an abrasion distance of 40 calculated from the material’s density. The volume loss of the sample was compared to the results m. The preparation of the abrasive sheet and its calibration using a standard reference compound achieved theimportant reference under same test conditions. The relative volume loss (∆Vrel ) was was afor very part of thethe method. calculatedAfter usingthe theabrasion following Equation test, the mass(1): loss of the specimen was determined and its volume was calculated from the material’s density. The volume loss of the sample was compared to the results ∆mt ∗ ∆mconst achieved for the reference under the∆V same rel =test conditions. The relative volume loss ( Δ Vrel ) was (1) calculated using the following Equation (1):
∆mr ∗ ρt
where ∆mt is the mass loss of the analyzed sample, mg; ∆mconst is the defined value of the mass loss of Δm t * Δmconst ΔVmg); rel = ∆mr is the arithmetic mean of the mass loss (1) the standard rubber sample (defined as 200 of three Δm r * ρ t 3 standard rubber samples, mg; and ρt is the density of the analyzed material, mg/mm . where Δ mt is the mass loss of the analyzed sample, mg; Δmconst is the defined value of the mass 2.2.2. loss The of Density the standard rubber sample (defined as 200 mg); Δm is the arithmetic mean of the mass loss r
density of material, mg/mm³. of three standard samples, mg; and ρt is the Determination ofrubber the density was performed according to the ISOanalyzed 2781:2008.
2.2.3. 2.2.2. The Fourier Transform Infrared (FTIR) Spectroscopy The Density The FT-IR spectra of elastomers recorded with a Tensor-27 spectrophotometer Determination ofthe the urethane density was performedwere according to ISO 2781:2008. (Bruker Optic GmbH, Ettlingen, Germany) equipped with a germanium crystal attenuated total 2.2.3. The Fourier Transform Infraredwere (FTIR) Spectroscopy reflectance (ATR) mode. The samples scanned over the frequency range of 4000–400 cm−1 at − 1 the resolution 2 cm spectra . The carbonyl hydrogen-bonding was determined based on the The of FT-IR of the urethane elastomers index were (R) recorded with a Tensor-27 spectrophotometer (Bruker Optic GmbH, Ettlingen, equipped with a germanium crystal intensities of the carbonyl stretching vibrations of freeGermany) (Afree ) and hydrogen-bonded (Abonded ) groups − 1 attenuated total reflectance (ATR) mode. The samples were scanned over the frequency range located at 1730 and 1700 cm , respectively. The R index was calculated according to Equationof (2): 4000–400 cm−1 at the resolution of 2 cm−1. The carbonyl hydrogen-bonding index (R) was determined based on the intensities of the carbonyl stretching A vibrations of free (Afree) and hydrogen-bonded R = bonded (2) (Abonded) groups located at 1730 and 1700 cm−1, respectively. The R index was calculated according to A f ree Equation (2):
the degree of the phase separation (DPS) and the degree of the phase mixing (DPM) were obtained through Equations (3) and (4). R DPS = (3) R+1 DPM = 1 − DPS
(4)
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2.2.4. The Wide-Angle X-ray Scattering (WAXS) The WAXS, moreover, an investigation was made with the use of wide-angle X-ray diffraction analysis using a diffractometer of the Empyrean (PANalytical, Almelo, The Netherlands) type. Filtered radiation from a lamp of Cu Kα and a wavelength of 0.154 nm were used. The step measurement method was used with scattering angles 2θ in the range of 10 to 40◦ and with a step size of 0.1◦ . 2.2.5. The Differential Scanning Calorimetry (DSC) The thermal transitions of the investigated polymer materials were studied using the DSC technique (Q100, TA Instruments, Wilmington, DE, USA). The samples were subjected to heating-cooling-heating cycles in the temperature range of −100 to 250 ◦ C. The standard heating rate of 10 ◦ C/min was applied. The melting temperature (Tm ) was determined as the maximum of the endothermic peak, while the glass transition temperature (Tg ) was set as the midpoint of the heat capacity change. 3. Results The main purpose of this study was to determine the effect of both the chemical composition and microstructure of polyurethane elastomers on their abrasive wear resistance. Understanding of this relationship was crucial to selecting the optimal composition for the most wear-resistant material. In the synthesis of PUR, the aliphatic polyethers or polyesters with molecular weights of 1000–2000 g/mol are mostly used as the SS. In our previous paper [22], we proved that PUR elastomers containing ether segments of Mn = 1800 g/mol revealed the higher abrasion resistance compared with PUR with ether segments of Mn = 1000 g/mol and the same SS content of 60 wt %. For that reason, the materials analyzed in this study contained oligomeric soft segments with the molecular mass of 2000 g/mol. Moreover, 1,4-butanodiol (BD) was used as the chain extender. The results of the wear abrasive resistance were calculated as a sample volume loss after the abrasive test determined from the mass loss and density (Table 3). At first, the effects of the various chemical compositions and different contents of the ether soft segments were studied (Figure 3). When the mass content of SS is increasing within 50–70%, the abrasive wear resistance is also increasing, reaching the highest value at the content of 70%. From these results, we decided that subsequently synthesized PUR materials should contain 70 wt % of SS, and the chemical structure of the polyol was made a variable for further analysis. From Figure 3, it is clear that the polyester soft segments, reaching the value of 81 ± 3 mm3 , improve the abrasive resistance more effectively than the polyether, for which the value of 95 ± 4 mm3 was calculated. Since the ester and carbonate groups reveal a similarity, the PUR elastomer with an aliphatic polycarbonate in the macromolecules was also included in the studies. However, its wear resistance took an intermediate position between polyester- and polyether-containing materials (Figure 4). As the additional modification in the chemical structure of the PUR samples, the diamine chain extender, MOCA, was used instead of BD. The reason for using MOCA was based on the assumption that the resulting PUR would contain the urea groups, which, compared with urethane groups, interact much more strongly with oxygen atoms. The overall results reflected in the abrasive wear resistance of PUR elastomers allowed us to determine that the most suitable composition was based on MDI, Polios 60/20 as the SS with 70% mass content, and MOCA as the chain extender. The average abrasive wear resistance for this sample was 73 ± 5 mm3 .
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atoms. The overall results reflected in the abrasive wear resistance of PUR elastomers allowed us to atoms. The overall results reflected in the abrasive wear resistance of PUR elastomers allowed us to determine that the most suitable composition was based on MDI, Polios 60/20 as the SS with 70% determine that the most suitable composition was based on MDI, Polios 60/20 as the SS with 70% mass content, and MOCA as the chain extender. The average abrasive wear resistance for this mass content, and MOCA as the chain extender. The average abrasive wear resistance for this sample was 73705 ± 5 mm3.3 Polymers 2017, 7 of 13 sample was9,73 ± 5 mm . 180 180
PUR/Ether/BD PUR/Ether/BD PUR/Carbonate/BD PUR/Carbonate/BD PUR/Ester/BD PUR/Ester/BD PUR/Ester/MOCA PUR/Ester/MOCA
3 Abrasive wear,mm mm 3 Abrasive wear,
160 160 140 140 120 120 100 100 80 80 60 60 45 45
50 50
55 55
60 60
65 65
Content of soft segments, wt% Content of soft segments, wt%
70 70
75 75
Figure PUR with various chemical composition andchemical different composition contents of Soft Figure 3. Abrasion Abrasion wear of polyurethane elastomers (PUR) with various and Figure 3. Abrasion wear of PUR with various chemical composition and different contents of Soft Segment The of 95% confidence interval indicated with interval ISO 2602:1980. different (SS). contents Soft Segment (SS). Theis95% confidence is indicated with ISO 2602:1980. Segment (SS). The 95% confidence interval is indicated with ISO 2602:1980.
Figure4. 4.Abrasion Abrasionwear wearof ofPUR PURversus versustheir theirhardness. hardness. Figure Figure 4. Abrasion wear of PUR versus their hardness.
The abrasive wear of PUR versus their shore D hardness are presented on Figure 4. For the The The abrasive abrasive wear wear of of PUR PUR versus versus their their shore shore D D hardness hardness are are presented presented on on Figure Figure 4.4. For For the the materials with the same chemical composition (PUR/Ether/BD), the following correlation can be materials with the same chemical composition (PUR/Ether/BD), the following correlation can materials with the same chemical composition (PUR/Ether/BD), the following correlation can be be defined: a highercontent contentofofthethe results in higher resistance. However, when different defined: SS SS results in higher wearwear resistance. However, when different polyols defined: aahigher higher content of the SS results in higher wear resistance. However, when different polyols aresuch used, such a correlation is not observed. are used, a correlation is not observed. polyols are used, such a correlation is not observed. The density of prepared PUR is a superposition the phase density derived SS,hard the The density of prepared PUR is a of of the softsoft phase density derived fromfrom SS, the The density of prepared PUR issuperposition a superposition of the soft phase density derived from SS, the hard phase density derived HS, and the interphase density. densities of the polyols used phase density derived fromfrom HS, and density. TheThe densities of the used for hard phase density derived from HS,the andinterphase the interphase density. The densities of polyols the polyols used for synthesis in 23 °C were 0.978 g/cm³ for polyether, 1.141 g/cm³ for polycarbonate, and 1.187 g/cm³ ◦ 3 3 3 synthesis in 23 C were 0.978 g/cm for polyether, 1.141 g/cm for polycarbonate, and 1.187 g/cm for synthesis in 23 °C were 0.978 g/cm³ for polyether, 1.141 g/cm³ for polycarbonate, and 1.187 g/cm³ for polyester. In our previous study [22], the density of 1.29 g/cm³ for the pure hard phase derived 3 for for polyester. polyester. In In our our previous previous study study[22], [22],the thedensity densityof of1.29 1.29g/cm g/cm³ for for the the pure pure hard hard phase phase derived derived from HS (MDI and 1.4 BD) was determined. Based on this data, it was found that the density values from from HS HS (MDI (MDI and and 1.4 1.4 BD) BD) was was determined. determined. Based Based on on this this data, data, itit was was found found that that the the density density values values of prepared PUR (Table 3) are consistent with the superposition of all phases and their content in the of prepared PUR (Table 3) are consistent with the superposition of all phases and their content in of prepared PUR (Table 3) are consistent with the superposition of all phases and their content in the polymers. the polymers. polymers.
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Table 3. The density of prepared PUR. The 95% confidence interval is indicated with SO2602:1980. Table 3. The density of prepared PUR. The 95% confidence interval is indicated with SO2602:1980. Materials Density, g/cm3 95% Confidence interval, g/cm3 95% Confidence interval, g/cm3 Materials Density, g/cm3 PUR_50/Ether/BD 1.1274 0.0191 PUR_50/Ether/BD 1.1274 0.0191 PUR_55/Ether/BD 1.1158 0.0126 PUR_55/Ether/BD 1.1158 0.0126 PUR_60/Ether/BD 1.1032 0.0070 PUR_60/Ether/BD 1.1032 0.0070 PUR_65/Ether/BD 1.0912 0.0074 PUR_65/Ether/BD 1.0912 0.0074 PUR_70/Ether/BD 1.0740 0.0027 PUR_70/Ether/BD 1.0740 0.0027 PUR_70/Carbonate/BD 1.1535 0.0082 PUR_70/Carbonate/BD 1.1535 0.0082 PUR_70/Ester/BD 1.2416 0.0158 PUR_70/Ester/MOCA 1.2508 0.0071 PUR_70/Ester/BD 1.2416 0.0158 PUR_70/Ester/MOCA 1.2508 0.0071
The The FTIR spectra forfor the ether-containing elastomers(Figure (Figure indicated along FTIR spectra the ether-containing elastomers 5) 5) indicated that,that, along with with the the increase of theofSSthe content, the carbonyl hydrogen bonding index,index, R, is decreasing (Table (Table 4). Specifically, increase SS content, the carbonyl hydrogen bonding R, is decreasing 4). R is defined as the ratio of theasamount groups connected by the hydrogen bond (1700 cm−1 ) Specifically, R is defined the ratioofofcarbonyl the amount of carbonyl groups connected by the hydrogen −1 ). (1730 to the amount of−1free carbonyl (1730 cm Moreover, while thewhile decrease in theinphase bond (1700 cm ) to the amount groups of free carbonyl groups cm−1). Moreover, the decrease the phase separation DPS, is observed, theof degree phase mixing, is increasing. This separation degree, DPS,degree, is observed, the degree phaseofmixing, DPM,DPM, is increasing. This means fact, the hard urethane hard phase domains, presented the microstructure, are getting that,means in fact,that, thein urethane phase domains, presented in thein microstructure, are getting smaller. This the alsonext reflects the next correlation: smaller or phase finer hard phaseand domains andDPM a higher This smaller. also reflects correlation: smaller or finer hard domains a higher result in DPM result in higher wear resistance in the case of PUR with polyether SS. higher wear resistance in the case of PUR with polyether SS.
Figure 5. FT-IR spectra contentlevels levels polyether segments. Figure 5. FT-IR spectraofofPUR PURwith with different different content of of polyether softsoft segments.
When comparing the FTIR spectra of PUR with the content of 70 wt % of different soft When comparing the FTIR spectra of PUR with the content of 70 wt % of different soft segments, segments, presented in Figure 6, substantial differences concerning both the hydrogen-bonded and presented in Figure 6, substantial differences concerning both the hydrogen-bonded and free carbonyl free carbonyl groups are observed as well as differences in the peak related to the –NH group. If the groups observed well as differences in the peak relatedistothe thedifferences –NH group. If hydrogen the key factor keyare factor affectingasthe abrasive performance of the polymers in the affecting the abrasive the polymers is the in theextender hydrogen bondings, bondings, then it performance explains our of motivation to use thedifferences diamine chain instead of thethen it explains our motivation to use the diamine chain extender instead of the butanediol one. Indeed, butanediol one. Indeed, the amine group, when reacting with the isocyanate, creates the urea group, the amine when reacting the isocyanate, creates the symmetrically urea group, which is characterized which group, is characterized by the with presence of –NH groups bonded on both sides of the by carbonyl of group. two bonded –NH groups belonging on to the urea moiety the HS result in The twice as –NH the presence –NHThe groups symmetrically both sides of theincarbonyl group. two strong hydrogen –NHingroup from the urethane group.compared This groups belonging tobonding the ureacompared moiety inwith thethe HSone result twicecoming as strong hydrogen bonding reflected by the widening of the peakthe corresponding to the wave in theby range 3300–3330of the withisthe one –NH group coming from urethane group. Thisnumber is reflected theofwidening cm−1, and is a consequence of the superposition of two peaks: –NH hydrogen bonding of the − 1 peak corresponding to the wave number in the range of 3300–3330 cm , and is a consequence of urethane group (3330 cm−1) and of the urea group (3300 cm−1). The peak centered at 1640 cm−1 the superposition of two peaks: –NH hydrogen bonding of the urethane group (3330 cm−1 ) and of corresponds to the hydrogen-bonded ordered urea carbonyl bond.
the urea group (3300 cm−1 ). The peak centered at 1640 cm−1 corresponds to the hydrogen-bonded ordered urea carbonyl bond.
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Figure 6. FT-IR spectra PUR withthe thevarious various chemical chemical compositions. Contents of the Figure 6. FT-IR spectra of of PUR with compositions. Contents of SS thefor SSallfor all materials is constant. materials is constant. Table 4. The carbonyl hydrogen bonding index (R), the degree of the phase separation (DPS), and the
Table 4. The carbonyl hydrogen bonding index (R), the degree of the phase separation (DPS), and the degree of the phase mixing (DPM) in the prepared PUR. degree of the phase mixing (DPM) in the prepared PUR. Sample A1730 * A1700 ** R *** DPS DPM PUR_50/Ether/BD 1.40 6.65 4.74 0.83 Sample A1730 * A1700 ** R *** DPS DPM 0.17 PUR_55/Ether/BD 1.73 7.33 4.25 0.81 0.19 PUR_50/Ether/BD 1.40 6.65 4.74 0.83 0.17 PUR_60/Ether/BD 1.70 6.56 3.86 0.79 0.21 PUR_55/Ether/BD 1.73 7.33 4.25 0.81 0.19 PUR_65/Ether/BD 3.65 3.86 0.79 PUR_60/Ether/BD 1.57 1.70 5.74 6.56 0.79 0.21 0.21 PUR_70/Ether/BD 2.20 3.65 0.69 PUR_65/Ether/BD 1.79 1.57 3.94 5.74 0.79 0.21 0.31 PUR_70/Carbonate/BD 0.683 2.20 0.41 PUR_70/Ether/BD 10.7 1.79 7.29 3.94 0.69 0.31 0.59 PUR_70/Ester/BD 0.433 0.683 0.30 PUR_70/Carbonate/BD 13.0 10.7 5.62 7.29 0.41 0.59 0.70 PUR_70/Ester/BD 11.7 13.0 3.21 + 5.62 0.30 0.70 0.78 0.275 0.433 0.22 PUR_70/Ester/MOCA PUR_70/Ester/MOCA 3.21 +multipeak 0.275 0.22 A: absorption intensity calculated as the11.7 area of Gaussian fitting [absorbance * 0.78 wavenumber]; A: absorption intensity calculated as free the area of Gaussian [absorbance * wavenumber]; * intensity of carbonyl. ** A1700:multipeak absorptionfitting intensity of hydrogen-bonded * A1730: absorption +: A1730 :carbonyl. absorption intensity carbonyl. ** A1700of : absorption intensity of hydrogen-bonded +: the sum of of thefree absorption intensities hydrogen-bonded carbonyl from ester (1700carbonyl. cm−1) −1 ) and urea (1640 cm−1 ). the sum of the absorption intensities of hydrogen-bonded carbonyl from ester (1700 cm and urea (1640 cm−1). *** R = A1700/A1730: carbonyl hydrogen bonding index. *** R = A1700 /A1730 : carbonyl hydrogen bonding index.
The wide-angle X-ray diffraction profiles (WAXS) of the polyether-containing PUR in Figure 7 do not show a clear effectdiffraction of the long-range order relatedoftothe thepolyether-containing crystallization of the HS, regardless The wide-angle X-ray profiles (WAXS) PUR in Figure 7 of the HS to SS ratio. In the case of the elastomer containing 50 wt % of soft segments, the peak on the do not show a clear effect of the long-range order related to the crystallization of the HS, regardless pattern is slightly broader; this is due to the superposition of two constituent peaks, and might be of the HS to SS ratio. In the case of the elastomer containing 50 wt % of soft segments, the peak on explained as the effect of the simple (primitive) arrangement. However, it declines along with the the pattern is slightly broader; this is due to the superposition of two constituent peaks, and might content of the soft phase. When we compare the WAXS patterns of PUR samples with different SS be explained effect the simple arrangement. However, it declines presentedas in the Figure 8, it of is clear that only(primitive) the PUR material with the polyester segment and BDalong as the with the content of the soft phase. When we compare the WAXS patterns of PUR samples with different chain extender reveals the effect of the ordered domains. For the same composition but with MOCA SS presented in Figure 8, it is clear that only material the polyester segmentdata and BD being used, the long-range arrangement is the not PUR observed. This with is consistent with literature where MOCA described outstanding chain extender as the[10,41–43], chain extender revealsis the effect as of an theexcellent orderedcross-linker domains.and Foran the same composition but with in polyurethane MOCA being used,systems. the long-range arrangement is not observed. This is consistent with literature data [10,41–43], where MOCA is described as an excellent cross-linker and an outstanding chain extender in polyurethane systems.
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Figure 7. WAXS patterns of PUR with the different contents of the polyether soft segment. Figure WAXSpatterns patternsofofPUR PURwith with the the different different contents Figure 7. 7.WAXS contentsof ofthe thepolyether polyethersoft softsegment. segment.
Figure 8. WAXS patterns of of PUR with various chemical compositions. Figure 8. WAXS patterns PUR with various chemical compositions.Contents Contentsofofthe thesoft softsegment segmentfor Figure 8. WAXS patterns of PUR with various chemical compositions. Contents of the soft segment all for materials is constant (SS = 70 wt %). all materials is constant (SS = 70 wt %). for all materials is constant (SS = 70 wt %).
ordertotoverify verify if the in in the PUR microstructure is formed by HS by or SS, In In order the crystalline crystallinephase phase PUR microstructure is formed HSDSC or SS, In order to verify if if the crystalline phase in thethe PUR microstructure is formed by HS or SS, DSC analysis has been employed, and the and tracesthe are traces shown in Figure 9. Ininthe case of9.the polyether-based DSC analysis has been employed, are shown Figure In the case of analysis has been employed, and the traces are shown in Figure 9. In the case of the polyether-basedthe elastomers, PTMO segments of Msegments n = 2000 g/mol make a soft phase exhibiting the glass transition in polyether-based elastomers, PTMO of Mnmake = 2000 g/mol make a soft phase exhibiting the glass elastomers, PTMO segments of Mn = 2000 g/mol a soft phase exhibiting the glass transition in the temperature range of −73 °C (PUR_50/Ether/BD) to −67 °C (PUR_70/Ether/BD); however, a part ◦ C (PUR_50/Ether/BD) ◦ C (PUR_70/Ether/BD); transition in the temperature range of − 73 to − 67 the temperature range of −73 °C (PUR_50/Ether/BD) to −67 °C (PUR_70/Ether/BD); however, a part of this phase also crystallized small melting endotherms betweenendotherms 0 °C (PUR_50/Ether/BD) however, a partis this phase is giving also crystallized giving small melting between 0 ◦ C of this phase is of also crystallized giving small melting endotherms between 0 °C (PUR_50/Ether/BD) and 5 °C (PUR_70/Ether/BD). Obviously, the effect of the glass transition is more pronounced as the ◦ (PUR_50/Ether/BD) and 5 C Obviously, (PUR_70/Ether/BD). Obviously, the effect of the glass transition and 5 °C (PUR_70/Ether/BD). the effect of the glass transition is more pronounced as the is soft phase content increases due to more significant changes of the specific heat. Similarly, the lower more asincreases the soft phase increaseschanges due to of more significant of the the lower specific softpronounced phase content due to content more significant the specific heat.changes Similarly, the content of the HS, the lower are both the melting temperature of the hard phase and the specific the Similarly, content of the HS, thethe lower are both the HS, melting temperature of the phase and the specific heat. lower content of the the lower are both thehard melting temperature of the heat of this phase transition. Although the ordered domains giving clear WAXS reflections have not heat of this phase transition. Although the ordered domains giving the clearordered WAXS reflections have not hard phase and the specific heat of this phase transition. Although domains giving clear been detected for PTMO-based polyurethanes in the whole range of PTMO content, the DSC been detected for PTMO-based polyurethanes in the whole range of PTMO content, the DSC WAXS reflections have not been detected for PTMO-based polyurethanes in the whole range of PTMO analysis reveals the evident endothermal effects assigned to the crystals melting during heating. analysis reveals the evident endothermal effects assigned to the crystals melting heating. content, the DSC analysis reveals the evident endothermal effects assigned toduring the crystals melting during heating.
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Figure DSC curves of PUR withdifferent different contents of the soft segment. First heating. Figure 9. DSC9.curves of PUR with contents of polyether the polyether soft segment. First heating.
The DSC thermograms of PUR elastomers with various polyols (Figure 10) indicate the clear Figure 9. DSC curves of PUR with different contents of the polyether soft segment. First heating.
meltingthermograms endotherm of the polyester soft phasewith whenvarious BD is used as the chain extender The DSC of PUR elastomers polyols (Figure 10) indicate the (PUR_70/Ester/BD). This proves that the diffraction peaks observed on the WAXS profiles are extender clear meltingThe endotherm of theofpolyester softwith phase when BD(Figure is used as thethechain DSC thermograms PUR elastomers various polyols 10) indicate clear associated with the soft phase. What is interesting iswhen that the same elastomer-containing diamine melting endotherm of the polyester soft phase BD is used as the chain extender (PUR_70/Ester/BD). This proves that the diffraction peaks observed on the WAXS profiles are does not reveal the melting effect of the the soft diffraction phase, nor the melting of the on hard phase which indicates (PUR_70/Ester/BD). This proves that observed the WAXS profiles are associatedcross-linking with the soft phase. What is interesting ispeaks that the same elastomer-containing of the material. Moreover, it is consistent with the literature data [10,40–42] where diamine associated with the soft phase. What is interesting is that the same elastomer-containing diamine MOCA isreveal described aseffect an excellent does not reveal the melting of the soft northe the melting ofhard thephase hardwhich phaseindicates which indicates does not the melting effect ofcross-linker. the softphase, phase, nor melting of the cross-linking of the material. Moreover, it is consistent with thethe literature where MOCA cross-linking of the material. Moreover, it is consistent with literaturedata data [10,40–42] [10,40–42] where MOCA is described as an excellent cross-linker. is described as an excellent cross-linker.
Figure 10. DSC curves of PUR with various chemical composition. Contents of the soft segment for all materials is constant (SS = 70%). First heating. Figure 10. DSC of curves of with PUR with various chemicalcomposition. composition. Contents of the for Figure4.10. DSC curves PUR various chemical Contents ofsoft thesegment soft segment for all Conclusions all materials is constant (SS = 70%). First heating. materials is constant (SS = 70%). First heating.
In this paper, a range of segmented linear polyurethane elastomers containing polyether, 4. Conclusions and polyester polyols as the soft segments were synthesized and characterized. The polycarbonate, 4. Conclusions mainIn purpose was toastudy of the polyol structure and the content on the abrasive this paper, rangethe ofeffect segmented linearchemical polyurethane elastomers containing polyether, wear resistance of PUR materials in order to explain the origin of their different wear performances. polycarbonate, polyester polyols as thelinear soft segments were synthesized and characterized. The polyether, In this paper, a and range of segmented polyurethane elastomers containing It waspurpose confirmed the higher the content of thechemical soft phase in a PUR the higher wear main wasthat to study the effect of the polyol structure andsample, the content on the the abrasive polycarbonate, andThis polyester as the soft(higher segments were and As characterized. resistance. results in polyols a better mixing DPMofvalue) insynthesized the microstructure. a wear resistance of PUR materials in phase order to explain the origin their different wear performances. the hard phase domains are smaller or finer and the interfacial area to volume ratio is The main consequence, purpose was to study the effect of the polyol chemical structure and the content on the It was confirmed that the higher the content of the soft phase in a PUR sample, the higher the wear increasing. These findings the motivation totocontinue thethe studies on PUR elastomers resistance. This results in a became better phase mixing (higher DPM value) in origin the microstructure. As a abrasive wear resistance of PUR materials in order explain of their different wear containing 70 the wt hard % ofphase various polyols. abrasion tests revealed that thearea polyester softratio phase consequence, domains areThe smaller or finer and the interfacial to volume is
performances. It was confirmed that the higher the content of the soft phase in a PUR sample, increasing. These findings became the motivation to continue the studies on PUR elastomers the highercontaining the wear resistance. This results in a better phase mixing (higher DPM value) in the 70 wt % of various polyols. The abrasion tests revealed that the polyester soft phase microstructure. As a consequence, the hard phase domains are smaller or finer and the interfacial area to volume ratio is increasing. These findings became the motivation to continue the studies on PUR elastomers containing 70 wt % of various polyols. The abrasion tests revealed that the polyester soft phase seems to be the most effective in improving the abrasive wear resistance if compared with the polyether and polycarbonate phases. This is explained by the higher cohesion of the polyester phase, because the carbonyl group in ester bonding makes much stronger hydrogen bonds than the ether group.
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It was also concluded that the crystallization ability is not critical for the abrasion wear performance. As the most promising material, we used the polyester-based PUR with the diamine chain extender. The tested sample revealed melting endotherm neither of the soft nor of the hard phase. This is most likely the reason that the calculated degree of phase mixing (DPM) is the highest for the selected material. Acknowledgments: This work was financially supported by National Science Centre in Poland, project Preludium 2015/19/N/ST8/01928. We thank Magdalena Kwiatkowska and Krzysztof Rucki (BEng) for providing the language support and the proof reading of this article. Author Contributions: Konrad Kwiatkowski conceived and designed the experiments; Małgorzata Nachman performed the experiments; Konrad Kwiatkowski and Małgorzata Nachman analyzed the data; Konrad Kwiatkowski and Małgorzata Nachman wrote the paper. Conflicts of Interest: The authors declare no conflict of interest.
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