Cardon, Ludwig

De Clerck, Karen

Wang, Sisi

Ghent University Academic Bibliography

1 INTRODUCTION 3D printing or additive manufacturing (AM) is a manufacturing process that enables the production of physical objects directly from digital part models by additive processes, whereby successive layers of ma-terials are deposited to fabricate the final parts. Ex-trusion-based AM such as fused filament fabrication (FFF), also known as fused deposition modeling (FDM), is a widely used, low-cost technique[Swetham, et al. 2017]. AM with poly-mers has been exploited in a number of innovative ways to produce materials and functional devises in many fields. A major challenge of extrusion-based AM is the lack of commercially available materials[Spoerk, et al. 2018] compared to those in well-established processes like injection molding or extrusion.  Poly(3-hydroxybutyrate) (PHB) is a biodegrada-ble thermoplastic with biocompatibility and ecologi-cal safety[Sharma, et al. 2016] and can be extruded, molded and spun using conventional plastic pro-cessing equipment[Arrieta, M. P., et al. 2014]. Bio-sourced PHB are used in 3D printing to broaden the material pool for FFF. PLA, also a biodegradable polymer is used to improve the printing and mechan-ical properties of PHB. Many people investigated the PLA/PHB blend for food package or other applica-tions[Arrieta, Marina P., et al. 2014], but PHB and PHB/PLA blend used in 3D printing have not yet been done. Within this research, filaments of PHB/PLA blends were produced and processed via extrusion based AM. Afterwards, mechanical and thermal properties were characterized.   2 EXPERIMENTAL 2.1 Sample preparation Polyactic acid (PLA 3D850) pellets, a grade devel-oped for manufacturing 3D printer monofilaments, was purchased from Natureworks. Polyhydroxy-butyrate (PHB P304) pellets were obtained from Bi-omer. Materials were dried over night at 45°C before processing. PHB/PLA blends with different compositions (80/20, 60/40, 40/60, 30/70, 20/80 by mass ratio) were produced into granules via twin screw extruder (Coperion ZSK18ML) with a screw diameter of 18 mm and L/D 40. A screw speed of 120 rpm and a temperature profile from 155°C to 190°C was used. The extrudates were water cooled and cut into gran-ules for the next processing step in the single screw extruder (Brabender PL2000 - screw diameter 19 mm and L/D 25) to fabricate consecutive filament with diameter of 1.75mm. The temperature profile was 160, 170, 180 and 190°C from feeding zone to die. The screw speed was set 30 rpm and hauling Polylactic acid/poly-3-hydroxybutyrate applications in Extrusion based Additive Manufacturing S. Wang*1, K. De Clerck2, L. Cardon1  1Centre for Polymer and Material Technologies CPMT, Department of Materials, Textiles and Chemical Engineering, Ghent University, Tech Lane Ghent Science Park Campus A, Technologiepark 915, 9052 Zwijnaarde, Belgium 2Centre for Textile Science and Engineering CTSE, Department of Materials, Textiles and Chemical Engineering, Ghent University, Tech Lane Ghent Science Park Campus A, Technologiepark 907, 9052 Zwijnaarde, Belgium *Corresponding author: Sisi.Wang@ugent.be          ABSTRACT: Polyhydroxybutyrate (PHB) is a polyhydroxyalkanoate (PHA), a polymer belonging to the pol-yesters class that are of interest as bio-derived and biodegradable plastics. PLA is a biodegradable material widely used in 3D printing. In this research, PHB/PLA filaments were produced to be used in extrusion based additive manufacturing. It was found, when adding more PHB into the PLA/PHB blend, samples can be 3D printed under lower temperature, thus saving energy. PHB has a bad adhesion on the printing bed due to warpage and shrinkage. Blending with PLA can solve this adhesion problem. Besides adhesion, modulus and tress at break increased when adding PLA. Elongation at break reached maximum with a PHB content of 40wt% as pure filament, while it showed highest value with 20wt% PHB for printed tensile bars. The impact strength increased slightly when adding PLA and reached maximum with 20wt% PHB. VST of PLA/PHB blend was always above 150°C due to the good crystallization effect of PHB. speed 8 m·min-1, allowing a uniform filament diame-ter. Pure PHB and PLA filaments were also pro-duced under same condition with processing temper-atures up to 185°C and 210°C, respectively, according to the processing temperatures mentioned in the corresponding datasheets. Blend was denoted as PHB/PLA x/y (e.g. PHB/PLA 80/20). All the pro-duced filaments were dried overnight at 45°C to re-move the moisture. The produced filaments were printed on a Felix 3.0 printer at a flow speed of 50 mm·s-1. PHB and its blends were printed at 180°C, PLA was printed at 210°C, and bed temperature was set as 55°C. The nozzle diameter was 0.35 mm. The layer thickness was set at 0.15 mm, infill rate of 100% and a crossed 45° raster printing angle were used. A dog-bone sample (type 1BA) was applied to tensile test ac-cording to ISO527. A rectangular sample (80×10×4 mm3) based on ISO 179 was applied to test the Charpy impact strength of printed part. 2.2 Melt flow index The rheology of the blends are characterized via melt flow index (MFI) test. Samples are tested under cer-tain temperature (180 to 210°C) with a load of 2,16 kg referring to ISO 1133. 2.3 Mechanical analysis Tensile property of filaments and printed bars were measured on an Instron 5565 machine with a force of 5 kN in combination with the Blue Hill software. The measurements are performed according ISO 527. The extensometer 2620-603 Instron with Gauge length 25 mm is used to calculate accurate results at the beginning of the stress-strain curve. A 1 mm·min-1 tensile rate is applied until 0.3% strain for determining the Young’s modulus. Afterwards 5 mm·min-1 is executed until the material breaks. Im-pact tests were conducted on a Tinius Olsen Impact model 503. Dimension of specimen was as described in the Charpy ISO 179 standard. A V-notch was ap-plied with a depth of 2 mm. The weight of pendulum was 0,462 kg, which supplies a nominal impact en-ergy of 2,82 J and a released velocity of 3,46 m·s-1. All tests were carried after 2 days conditioning in standard atmosphere (23°C and 50% humidity). At least five samples were tested to get an average val-ue. 2.4 Thermal analysis To know the crystallization behavior of different samples, DSC measurement was taken on the DSC machine (NETZSCH 204 F1). Samples were heated from room temperature to 200°C and kept at such temperature for 5 min to erase the heat history, then cooled to 20°C at cooling rate of 10°C min-1 and heated up to 200°C again at heating rate of 10°C min-1. Crystallization peak (Tc) and enthalpy (∆Hc) were recorded from first cooling curve. Cold crystal-lization peak (Tcc) and enthalpy (∆Hcc), melt peak (Tm) and fusion enthalpy (∆Hm) can be recorded from second heating curve. To know the effect of printing history on samples, printed bars were heat from 10°C to 200°C at 10°C min-1, heating curves were recorded. The Vicat softening temperature (VST) of the samples were investigated using a thermal defor-mation, Vicat softening temperature tester (CEAST 6510). Printed samples with same dimension of im-pact bars were used to determine the Vicat softening temperature. The test was performed in accordance with ISO306:1994 in methyl silicone oil bath at a heating rate of 120°C·h-1 under a speciﬁc load of 10N.  3 RESULTS AND DISCUSSION 3.1 Melt flow index 180 190 200 21001020304050607080MFI, g 10min-1Temperature, C PHB PHB/PLA 80/20 PHB/PLA 60/40 PHB/PLA 40/60 PHB/PLA 30/70 PHB/PLA 20/80 PLA Figure 1. Melt flow index of samples at different temperature.   Rheological data is an important parameter for 3D printing applications to achieve a good and stable flow [Ramanath, et al. 2008, Wang, S., et al. 2017]. MFI data for samples at different temperatures were measured; results were shown in Figure 1. MFI val-ue increases with testing temperature. MFI increases from 2.0±0.2 to 8.6±0.5 g·10min-1 for PLA filament at temperature from 180 to 210°C. The MFI value of PHB and PHB/PLA blends are much bigger than that of PLA, and it increases a lot with testing tempera-ture. It is noticed that PHB is more sensitive to tem-perature than PLA. Based on 3D printing pretests, samples can be printed in the area shown in black rectangle in figure 1. PHB and PHB/PLA can be printed under lower temperature compare to PLA, thus saving energy. Based on the previous research[Wang, S., et al. 2017], it is recommended to print samples with a MFI value close to/above 10 g·10min-1. Based on this investigation, pure PHB and blends were printed at 190°C, pure PLA was printed at 210°C. During the tests it was found PHB has a bad ad-hesion on the printing bed due to warpage and shrinkage. The adhesion improved with blends con-taining PLA or when printing on blue tape. Blends which contain less than 60wt% PHB were printed on standard printing bed. 3.2 Mechanical property Tensile and impact data of samples were shown in figure 2 and table 1. As expected, the properties of printed bars are not as good as that of the filaments due to the existence of voids in printed parts[Wang, L., et al. 2017]. Modulus and stress of samples in-crease with more PLA in the blend because of the high tensile modulus and strength of PLA[Jalali, et al. 2016]. Similar results can be seen in other stud-ies[Bartczak, et al. 2013]. Pure PHB and PLA showed low elongation, while toughness of blends increased slightly compared to pure material. Elon-gation at break reached maximum with a PHB con-tent of 40wt% for filament, and it showed highest value with 20wt% PHB for printed tensile bars. The slight increment of elongation is due to the poor miscibility between PLA and PHB[Lin, et al. 2016]. To improve the tensile property even more, the mor-phological structure of the blend should be modified in future studies. The impact strength increased slightly when adding PLA and reached maximum with 20wt% PHB. Bartczak [Bartczak, et al. 2013] and Lai[Lai, et al. 2017] investigated the toughness of PLA/atactic PHB (a-PHB) blend, finding a signif-icant increase in the ductility of blend because of the plasticization effect of a-PHB.  05001000150020002500300035004000PLAPHB/PLA20/80PHB/PLA30/70PHB/PLA40/60PHB/PLA60/40PHB/PLA80/20modulus, MPa modulus of filament modulus of barPHB0204060 stress of filament stress of barstress at maximum load, MPa(a)  Figure 2. Mechanical properties (a) modulus and stress at max-imum load, (b) Charpy impact strength and strain at break for filament and printed bars.   Table 1.  Mechanical data of PHB/PLA blends. Sample Modulus, MPa Stress at maximum load, MPa Strain at break, % Charpy impact strength, kJ·m-2 filament PHB 1215±94 20.5±0.4 5.3±0.2 - PHB/PLA 80/20 2121±91 30.7±0.3 10.5±0.5 - PHB/PLA 60/40 2658±305 37.2±0.4 13.6±4.7 - PHB/PLA 40/60 3187±180 46.2±1.1 44.1±12.0 - PHB/PLA 30/70 3475±95 52.0±2.1 31.3±12.6 - PHB/PLA 20/80 3404±147 53.6±1.5 15.2±10.2 - PLA 3537±288 60.3±1.5 14.1±7.2 - Printed bar PHB 997±151 19.4±1.3 5.5±0.3 3.5±0.6 PHB/PLA 80/20 1498±115 25.3±1.0 7.9±1.5 3.1±0.4 PHB/PLA 60/40 2408±277 31.0±0.5 4.5±0.5 3.1±0.4 PHB/PLA 40/60 3182±95 42.4±0.7 5.7±1.4 3.6±0.9 PHB/PLA 30/70 3303±140 46.9±1.0 6.6±1.1 4.3±0.2 PHB/PLA 20/80 3189±79 48.5±0.7 8.2±2.2 5.0±0.5 PLA 3671±280 61.2±2.5 3.2±0.5 4.2±0.5  In general, PHB/PLA 20/80 showed best mechan-ical properties among all these samples. Mass ratio of 20/80 can be used to acquire samples with good mechanical properties. 3.3 Thermal property DSC curve of filaments and printed bars were shown in figure 3. In figure 3(a), there is sharp crystalline peak (Tc) in the cooling curve for PHB (115.0°C), which means PHB has good melt crystallization abil-ity. Tc shift to lower temperature after PLA was add-ed (108.1°C for PHB/PLA 20/80), which means melt crystallization ability of blend weaken. Pure PLA has no crystalline peak, which means it crystallizes very slow during the cooling process[Jalali, et al. 2016]. In figure 3(b), PLA shows a big cold crystal-lization peak but as for PHB no cold crystal peak has been noticed in the second heating curve, confirming PHB’s good crystallization ability. The PHB/PLA blends show similar crystallization behavior to pure PHB, confirming the nucleating agent of PHB on PLA, which significantly improves the melt crystal-lization ability of PLA3D[Arrieta, M. P., et al. 2014]. The melting point of PHB is smaller than PLA, which results in a bigger MFI for the blend, as discussed in section 3.1.  DSC results of printed bars are illustrated in fig-ure 3(c). Pure PHB and PHB/PLA blends contain more than 60wt% PHB have no cold crystal peak and the glass transition platform looks flat, indicat-ing high crystallinity of printed samples which may be unfavorable to the printing quality. As pretest of 3D printing showed, blends contain more PHB will warp and cannot adhere to platform well. So to ob-tain a well printed part, less than 60wt% of PHB should be used. With higher percentage addition of PLA, the glass transition temperature (Tg) and cold crystallization temperature (Tcc) shift to the right and the cold crystallization peak becomes bigger, which means a decreased crystallization ability and lower crystallinity of the blends. This means that PLA with low crystallinity is not suitable for heat resistance applications.  40 60 80 100 120 140 160 180 200 220Tc=108,1 C(a)Heat flow, W/gendo  Temperature, Cfirst cooling curvePLAPHB/PLA 20/80PHB/PLA 30/70PHB/PLA 40/60PHB/PLA 60/40PHB/PLA 80/20PHBTc=115,0 C 40 60 80 100 120 140 160 180 200 220Tm=163,4 CTm=175,3 CTcc=101,3 CHeat flow, W/gendo  Temperature, Csecond heating curvePLAPHB/PLA 20/80PHB/PLA 30/70PHB/PLA 40/60PHB/PLA 60/40PHB/PLA 80/20PHB(b)Tg=57,4 C  40 60 80 100 120 140 160 180 200 220Tm=171,9 CTm=177,0 Cendo Temperature, CDSC curve for printed bar Heat flow, W/g(c)PHBPHB/PLA 80/20PHB/PLA 60/40PHB/PLA 40/60PHB/PLA 30/70PHB/PLA 20/80PLA Figure 3. DSC curve (a) first cooling, (b) second heating curve of filaments, (c) DSC curve for printed bars.  Vicat softening temperature (VST) of PHB/PLA was measured in following part to know the heat re-sistance of the samples. Pure PHB and samples with PHB inside always showed a VST above 140°C due to the good crystallization effect of PHB. Pure PLA has a rather low VST (61.6°C) due to its low glass transition temperature and the slow crystallization rate unless it is fully crystallized[Jalali, et al. 2016, Tsuji, et al. 1995]. By adding PHB, PLA can obtain a higher crystallinity, as it can sufficiently crystalize during the cooling phase of the printing process, which can lead to better heat resistance and strength. According to the DSC and VST results, PHB has a fast crystallization during printing. Pure PLA has a slow crystallization resulting in poor heat resistance, while PHB/PLA blends showed good thermal per-formance.  Table 2. Vicat softening temperature of PHB/PLA blends. sample PHB/PLA Mass ratio PHB 80/20 60/40 40/60 30/70 20/80 PLA VST, °C 146.6 143.8 153.3 152.9 153.0 153.4 61.6  4 CONCLUSION Bio-based PHB/PLA filaments used in extrusion based additive manufacturing were developed and characterized. It was found, when adding more PHB into the PLA/PHB blend, melt flow index drops and samples can be 3D printed under lower temperature, thus saving energy. PHB has a bad adhesion on the printing bed due to warpage and shrinkage. PLA was added to improve the adhesion. It was found that PHB content should not be more than 60wt% to get samples with good printing quality. Modulus and stress at break increased a lot after adding PLA thanks to PLA’s high stiffness. Elongation at break reached maximum with a PHB content of 40wt% as pure filament, while it showed highest value with 20wt% PHB for printed tensile bars. The impact strength increased as well when adding PLA and reached maximum with 20wt% PHB, which is com-parable for tensile strain. VST of PLA/PHB blend was always above 150°C due to the good crystalliza-tion effect of PHB. In summary, more PHB will lead to higher crys-tallinity, better heat resistance, and consume less en-ergy by printing at lower temperature. However, pure PHB is not a good candidate for low cost extru-sion based AM. To obtain samples with good print-ing quality and good mechanical properties, PLA should be added. PHB/PLA 20/80 blend showed best general performance, which can be considered as a potential blend for 3D printing in future research.  5 REFFERENCE Arrieta, M. P.; Fortunati, E.; Dominici, F.; Rayon, E.; Lopez, J.; Kenny, J. M., 2014, Multifunctional PLA-PHB/cellulose nanocrystal films: processing, structural and thermal properties. Carbohydr Polym 107, 16-24. Arrieta, M. P.; López, J.; Hernández, A.; Rayón, E., 2014, Ternary PLA–PHB–Limonene blends intended for biodegradable food packaging applications. European Polymer Journal 50, 255-270. Bartczak, Z.; Galeski, A.; Kowalczuk, M.; Sobota, M.; Malinowski, R., 2013, Tough blends of poly(lactide) and amorphous poly([R,S]-3-hydroxy butyrate) – morphology and properties. European Polymer Journal 49 (11), 3630-3641. Jalali, A.; Huneault, M. A.; Elkoun, S., 2016, Effect of thermal history on nucleation and crystallization of poly(lactic acid). Journal of Materials Science 51 (16), 7768-7779. Lai, S.-M.; Liu, Y.-H.; Huang, C.-T.; Don, T.-M., 2017, Miscibility and toughness improvement of poly(lactic acid)/poly(3-Hydroxybutyrate) blends using a melt-induced degradation approach. Journal of Polymer Research 24 (7). Lin, K.-W.; Lan, C.-H.; Sun, Y.-M., 2016, Poly[(R)3-hydroxybutyrate] (PHB)/poly(l-lactic acid) (PLLA) blends with poly(PHB/PLLA urethane) as a compatibilizer. Polymer Degradation and Stability 134, 30-40. Ramanath, H. S.; Chua, C. K.; Leong, K. F.; Shah, K. D., 2008, Melt flow behaviour of poly-ɛ-caprolactone in fused deposition modelling. J Mater Sci Mater Med 19 (7), 2541-50. Sharma, M.; Dhingra, H., 2016, Poly-β-hydroxybutyrate: A Biodegradable Polyester, Biosynthesis and Biodegradation. British Microbiology Research Journal 14 (3), 1-11. Spoerk, M.; Arbeiter, F.; Raguž, I.; Weingrill, G.; Fischinger, T.; Traxler, G.; Schuschnigg, S.; Cardon, L.; Holzer, C., 2018, Polypropylene Filled With Glass Spheres in Extrusion-Based Additive Manufacturing: Effect of Filler Size and Printing Chamber Temperature. Macromolecular Materials and Engineering, 1800179. Swetham, T.; Reddy, K. M. M.; Huggi, A., 2017, A Critical Review on of 3D Printing Materials and Details of Materials used in FDM. Tsuji, H.; Ikada, Y., 1995, Properties and morphologies of poly (L-lactide): 1. Annealing condition effects on properties and morphologies of poly (L-lactide). Polymer 36 (14), 2709-2716. Wang, L.; Gramlich, W. M.; Gardner, D. J., 2017, Improving the impact strength of Poly(lactic acid) (PLA) in fused layer modeling (FLM). Polymer 114, 242-248. Wang, S.; Capoen, L.; D’hooge, D. R.; Cardon, L., 2017, Can the melt flow index be used to predict the success of fused deposition modelling of commercial poly(lactic acid) filaments into 3D printed materials? Plastics, Rubber and Composites 47 (1), 9-16.   

Polylactic acid/poly-3-hydroxybutyrate applications in extrusion based additive manufacturing

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Polylactic acid/poly-3-hydroxybutyrate applications in extrusion based additive manufacturing

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