Danimer Scientific - Senior Design Day

Authors

Anika Callanan
Miraz A. Sadi
Quinn Taylor

Mentors

Mitch Anthamatten and Melodie Lawton ( Department of Chemical Engineering)

Abstract

The crystallization speed of a polymer can be a limiting step in the production of products. The sponsor of the project, Danimer Scientific, posed the problem of slow crystallization, and the goal of increasing the crystallization temperature (Tc) of the biodegradable polymer, poly(3-hydroxypropionic acid) (P3HP). A bio-based nucleator was used to increase the polymer’s Tc. A DSC screen was conducted using several bio-based additives where orotic acid (OA) was the most promising candidate. To study the scaled-up production of the polymer, a temperature-controlled mold was designed to study isothermal crystallization during the process.

Introduction

Background:
The production of non-biodegradable plastic is projected to triple over the next decades, potentially leading to a quadrupling in plastic pollution in oceans (The Guardian, 2016).

P3HP is an emerging biodegradable polymer produced by Danimer Scientific.

The polymer has a long crystallization time, prompting the exploration of bio-based additives to accelerate crystallization and reduce processing time.

The Tc of a polymer is the temperature at which the polymer organizes itself into a crystalline structure.

Nucleators decrease the energy barrier for crystallization, increasing the temperature that crystallization occurs because less energy has to be put in to overcome the barrier [1].

Nucleators increase the number of crystallization sites, impacting crystal size and thus, mechanical properties

Certain biobased additives increase the crystallization speed of similar polymers such as polyhydroxyalkanoate [2] and poly(L-lactide) [3].

Objective:

To utilize a bio-based nucleator to increase the Tc of P3HP, enhancing process efficiency
To scale up the process of crystallizing the polymer by creating a tool to control isothermal crystallization for an industrial process

Methodology

Full Process

Additive selection
Making pellets (done at Danimer Scientific)
Injection into temperature-controlled mold
Wait 72 hours after production
Scaled-up property testing

Characterization of Nucleators

Figure 2: DSC exotherm of neat P3HP and 1% OA

Differential Scanning Calorimetry (DSC) and Polarized Optical Microscope (POM) were used to select an additive and evaluate its effect on P3HP on a bench scale (powder).

DSC produced an exotherm showing the Tc
Gel Permeation Chromatography (GPC) evaluated the molar mass degradation after DSC
POM qualitatively analyzed crystal structures

Scale Up:

The process was scaled up using a temperature-controlled mold for an injection molder which produced dog bones for mechanical property testing.

Morgan Press melted pellets and injects into mold
Cooling channels machined into aluminum block and top of mold
Tensile testing using Instron to obtain Young’s Modulus (YM)
DSC run on dog bones show scaled-up Tc changes

Figure 3: Experimental setup A) Morgan Press connecting to chiller B) temperature-controlled mold C) original and elongated dog bones

Design of Experiments (DOE)

Factors

Levels

Responses

Mold Temperature

20˚C, 25˚C, 30˚C (Neat)

35˚C, 40˚C, 45˚C (1% OA)

Young’s Modulus,

Additive Loading

0% OA (neat), 1% OA

Results

Characterization

OA was found to be the most effective nucleator for P3HP.

OA increased Tc more than the other additives
GPC results showed OA as the only nucleator adding thermal stability

Figure 4: Screening Results for 5% by mass nucleator and neat polymer

POM images showed OA as an effective nucleator.

Neat P3HP and 1% OA were heated to 140°C, and cooled to their respective Tc
OA allowed crystals to form more homogenously than when the polymer lacked a nucleator
Crystal sizes are smaller with 1% OA, indicating an increased number of nucleation sites, preventing crystals from reaching larger sizes

Figure 5: POM images A) Neat P3HP melt at 140°C. B) Neat P3HP at its Tc of 25°C. C) 1% OA melt at 140°C. D) 1% OA at its Tc of 40°C.

Scale Up

Tensile testing showed:

Increased mold temperature yielded a higher YM product
Additive loading had little effect on YM

Neat and 1% OA show different YM trends:

YM for 1% OA increases with increased mold temperature
Neat remains inconclusive
Limited material prevented further analysis of neat P3HP
Air bubble in a neat dog bone resulted in lower YM
1% OA showed increasing YM with increasing mold temperature

The scaled-up 1% OA polymer product also showed an increase in Tc when compared to the neat dog bones.

Larger increase between neat and OA Tc for scaled-up process compared to bench scale
Both show statically significant change in Tc

Conclusions and Future Work

Conclusions:

The Tc of P3HP was increased by 10°C when scaled up
A 10°C increase in the mold temperature increased the YM of the scaled-up 1% OA product by roughly 20%.
The development of a scaled-up injection molding process with controlled crystallization using a custom cooling mold

Future Work:

Compound mixing to evaluate different OA loadings to determine optimal percent to maximize Tc increase
Optimizing Morgan Press parameters for scale up process (injection pressure, coolant temperature, injection speed) to determine which conditions eliminate air bubbles
Use a larger sample size to help support the above preliminary results

Acknowledgments

Team Parkour! would like to thank Prof. Lawton and Prof. Anthamatten for advising us this semester. We would like to thank Clair Cunningham, Jeff Lefler, Bill Mildenberger, and Prof. Kelley for assisting in the design and build. Additionally, we want to express our thanks to Kimberly Clem and Ben Carlson for helping us through this project. Finally, we would like to thank Dr. Chris DeRosa and Danimer Scientific for sponsoring this project and the Department of Chemical Engineering for their support.

References

1.Zhang, X., Meng, L., Li, G., Liang, N., Zhang, J., Zhu, Z. and Wang, R. (2016), Effect of nucleating agents on the crystallization behavior and heat resistance of poly(l-lactide). J. Appl. Polym. Sci., 133, 42999.

2.Bledsoe, J., Crane, G., and Locklin, J. Beyond Lattice Matching: The Role of Hydrogen Bonding in Epitaxial Nucleation of Poly(hydroxyalkanoates) by Methylxathines. Applied Polymer Materials. 2023.

3.Qiu, Zhaobin and Li Zhisheng. Effect of Orotic Acid on the Crystallization Kinetics and Morphology of Biodegradable Poly(L-lactide) as an Efficient Nucleating Agent. I&EC Research. 2011.

4.DeRosa, Chris. “Nucleation of Poly(Propiolactone).” Danimer Scientific 2023.