Dynamic local temperature control in micro‐injection molding: Effects on poly(lactic acid) morphology

Meo, Annarita De; Santis, Felice De; Pantani, Roberto

doi:10.1002/pen.24784

Cited by 18 publications

(7 citation statements)

References 23 publications

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“…This means that the crystalline structures detected in our samples had to be due to flow-induced crystallization, and their fibrillary morphology confirms this interpretation [50]. …”

Section: Resultssupporting

confidence: 67%

“…It is worth mentioning that the PLA grades adopted in this work, and generally all the commercial grades of PLA, had crystallization times (in quiescent conditions) much longer than the processing times of injection molding. This means that the crystalline structures detected in our samples had to be due to flow-induced crystallization, and their fibrillary morphology confirms this interpretation [ 50 ].…”

Section: Resultssupporting

confidence: 67%

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Replication of Micro- and Nanofeatures in Injection Molding of Two PLA Grades with Rapid Surface-Temperature Modulation

2018

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The production by injection molding of polymeric components having micro- and nanometrical surfaces is a complex task. Generally, the accurate replication of micro- and nanometrical features on the polymeric surface during the injection-molding process is prevented by of the low mold temperature adopted to reduce cooling time. In this work, we adopt a system that allows fast heating of the cavity surface during the time the melt reaches the cavity, and fast cooling after heater deactivation. A nickel insert with micro- and nanofeatures in relief is located on the cavity surface. Replication accuracy is analyzed by Atomic Force Microscopy under different injection-molding conditions. Two grades of polylactic acid with different viscosity have been adopted. The results indicate that the higher the cavity surface temperature is, the higher the replication accuracy is. The viscosity has a significant effect only in the replication of the microfeatures, whereas its effect results are negligible in the replication of nanofeatures, thus suggesting that the interfacial phenomena are more important for replication at a nanometric scale. The evolution of the crystallinity degree on the surface also results in a key factor on the replication of nanofeatures.

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“…This means that the crystalline structures detected in our samples had to be due to flow-induced crystallization, and their fibrillary morphology confirms this interpretation [50]. …”

Section: Resultssupporting

confidence: 67%

Section: Resultssupporting

confidence: 67%

Replication of Micro- and Nanofeatures in Injection Molding of Two PLA Grades with Rapid Surface-Temperature Modulation

2018

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“…Several methodologies can be adopted for controlling cavity surface temperature during the injection molding process, such as proximity heating [28,29], infrared heating [30], and electrical heating [31,32]. Another possibility to control the mold temperature was proposed by Minh and coworkers [33], who developed an external gas-assisted mold temperature control for improving the performance of thin rib parts.…”

Section: Introductionmentioning

confidence: 99%

Effect of Rapid Mold Heating on the Structure and Performance of Injection-Molded Polypropylene

et al. 2020

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The tailoring by the process of the properties developed in the plastic objects is the more effective way to improve the sustainability of the plastic objects. The possibility to tailor to the final use the properties developed within the molded object requires further understanding of the relationship between the properties of the plastic objects and the process conduction. One of the main process parameters that allow adjusting the properties of molded objects is the mold temperature. In this work, a thin electrical heater was located below the cavity surface in order to obtain rapid and localized surface heating/cooling cycles during the injection molding process. An isotactic polypropylene was adopted for the molding tests, during which surface temperature was modulated in terms of values and heating times. The modulation of the cavity temperature was found able to control the distribution of relevant morphological characteristics, thus, properties along the sample thickness. In particular, lamellar thickness, crystallinity distribution, and orientation were analyzed by synchrotron X-ray experiments, and the morphology and elastic modulus were characterized by atomic force microscopy acquisitions carried out with a tool for the simultaneous nanomechanical characterization. The crystalline degree slightly increased with the cavity temperature, and this induced an increase in the elastic modulus when high temperatures were adopted for the cavity surface. The cavity temperature strongly influenced the orientation distribution that, on its turn, determined the highest values of the elastic modulus found in the shear layer. Furthermore, although the sample core, not experiencing a strong flow field, was not characterized by high levels of orientation, it might show high values of the elastic modulus if temperature and time during crystallization were sufficient. In particular, if the macromolecules spent adequate time at temperatures close to the crystallization temperature, they could achieve high levels of structuring and, thus, high values of elastic modulus.

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“…After that, by switching off the heaters the rapid cooling led the surfaces in less than 10 s to 60 • C. Without extracting the sample from the mold the preparation of each sample included a second step in which an isothermal step (crystallization step) involved only an area of the injected samples. A temperature of 105 • C was applied for 500 s. In these conditions, a low crystallization time is expected (De Meo et al, 2018).…”

Section: Resultsmentioning

confidence: 99%

Micromolded Polylactid Acid With Selective Degradation Rate

2019

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Poly(Lactic Acid), PLA represents a very interesting polymer for industrial applications because of its good processability, the possibility of being obtained from renewable sources, good physical properties, biocompatibility, and biodegradability. The major depolymerization mechanism and the step that controls the rate of PLA biodegradation in compost is represented by the hydrolysis. The characteristic of being degradable is not per se an advantage: the inclination to degrade in the presence of water represents a limit for specific industrial applications, especially for durable components that are designed for long-period utilization such as in the automotive, electronic, and agricultural sectors, as well as in medical applications. Being able to control the degradation rate would be a real advantage: a product should preserve its characteristics during processing and for a time comparable to its application but should be nevertheless fully biodegradable at longer times. Furthermore, a gradient of properties could allow producing samples in which some portions degrade at a faster rate and some others at a slower one. Different methods can be used to influence the degradation rate of PLA, some examples are blending, copolymerization and surface modification. However, these change the physical properties of the material. Any factor influencing the rate of hydrolysis can affect the biodegradation process. The objective of this work is verifying the possibility to modulate the rate of degradation in the same part, in time and at different rates. The method is represented by a technique that influences locally the morphology of the samples. Biphasic samples (half amorphous and the other half crystalline) were obtained by micro-injection molding and the degradation process was monitored by means of hydrolysis tests. The analysis confirmed the crystalline regions show a slightly better resistance to the hydrolysis compared to the amorphous.

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Dynamic local temperature control in micro‐injection molding: Effects on poly(lactic acid) morphology

Cited by 18 publications

References 23 publications

Replication of Micro- and Nanofeatures in Injection Molding of Two PLA Grades with Rapid Surface-Temperature Modulation

Replication of Micro- and Nanofeatures in Injection Molding of Two PLA Grades with Rapid Surface-Temperature Modulation

Effect of Rapid Mold Heating on the Structure and Performance of Injection-Molded Polypropylene

Micromolded Polylactid Acid With Selective Degradation Rate

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