PLA is rarely used in technical applications. The polymer is considered to be very sensitive to hydrolysis. A research project is now showing just how much.

Disposable cutlery and packaging are a classic area of application for PLA. In more demanding areas, however, the biopolymer is only used very rarely.

16:9

Polylactid

Kunststoff Werkstoffe

Thermoplaste

Biokunststoffe

Materialcharakterisierung

Software

Simulation

How Sensitive Is PLA to Hydrolysis?

Shape-changing structures (smart structures) are able to change their shape in response to external stimuli. The change of shape is self-induced and requires no artificial energy input. In view of the increasing demand for efficiency and resource conservation, shape-changing (smart) materials offer a sensible approach to integrating functionalities into a component without giving rise to additional energy and material costs. Even greater sustainability is achieved if the components are produced from bioplastics.

Prototype of a weather-sensitive smart facade system

Bioplastics for Shape-Changing Structures

Additive Fertigung

Green Shape Changers

The raw material used to produce Europlex Film LJ 21123/123 is derived from non-genetically modified sugarcane.

 Europlex Film LJ 21123/123 consists of a renewable raw material and can be shaped flexibly.

Röhm Is Developing Thermoformable PLA Films

The K 2022 offered an immense range of innovations and application examples for – and with more – sustainable materials. Interestingly hereby was that bio-based versions were extremely popular.

Shoes made from waste gas: genetically modified bacteria produce ethanol from waste gas, which is then used to create plastic, e.g. for the Cloudprime shoes from On.

Thermoplastische Elastomere

Silikone

Messe K-Kunststoffmesse

kunststoffe-international.com

kunststoffe.de

Masterbatches

Additive

Polyethylen

Streifinger, Florian

Polyamide

Effektpigmente

Polypropylen

Faserverbundwerkstoffe

Andere Werkstoffe

Kunststoff-Rezyklat

Silikonkautschuk

Kautschuk / Elastomere

Is Bio the New Standard?

A case study shows that the biodegradability of plastics in healthcare offers hardly any advantages. The use of bio-based raw materials also has its hurdles.

The rack seen  in nature with which it should have been in harmony after the completion of this study.

Spritzgießen

Kunststoffverarbeitung: Verfahren

Medizintechnik

Qualitätssicherung Kunststoff

Qualitätssicherung

Medizinprodukte

Do Bioplastics Have a Future  in Healthcare?

The new Horizon Europe-funded Greco project aims to demonstrate the life cycle and techno-economic feasibility of greener and safer bioplastics value chains for the food packaging sector, based on a safe and sustainable-by-design strategy.

Food packaging: Development of PLA copolymers by reactive extrusion and on the production of additives by mechanochemistry.

An ice-cream parlor worker is preparing some raspberry and blackberries on the roll machine using tongs

Verpackungsmaterial

Logistik

Kreislaufwirtschaft

Greener and Safer Bioplastics for Food Packaging

Polymer specialist Uhde Inventa Fischer (UIF) has entered into a partnership with Praj Industries Ltd (PIL) to provide an end-to-end PLA production solution.

At the signing (from left to right): Dr. Pramod Kumbhar, President and Chief Technology Officer at Praj Industries; Dr. Ashvini Shete, Business Head – Biopolymers at Praj Industries; Udo Mühlbauer, Head of R&D at Uhde Inventa-Fischer (front); Stefan Bartz, VP Sales at Uhde Inventa-Fischer (back)

Uhde Inventa Fischer and Praj Industries Join Forces

The production of particle foams with low densities and at the same time high molding quality is difficult, so the development of foamed polymer blends could simplify the entire processing.

Blend

Partikelschäumen

Schäumen / Reaktive Verarbeitung

Study of expandable PLA particle foams – Influence of the blend system on processability and properties

Textile structures can be equipped with shape-changing properties at all stages of their production. So-called 4D textiles are created.

4D materials are ideal for personalized medical technology such as orthoses.

Formverändernde Textilien, sogenannte 4D-Textilien, bieten beispielsweise für die Medizintechnik große Vorteile. Herstellen lassen sie sich mittels FDM-Druck.

From Static to Adaptive Products with 4D Textiles

Into the Fourth Dimension  with 3D Printing

Three solutions for increasing the productivity in the automotive, medical and packaging industries are presented by Tederic at K 2022 with the Neo injection molding machine series. T

The Neo·Ec combines electrical and hydraulic drives.

Mehrkomponenten-Spritzgießen

Spritzprägen

Spritzgießmaschinen

Kunststoffverarbeitung: Maschinen und Komponenten

Applications in Three Key Sectors

At Interpack TotalEnergies Corbion exhibits its polylactide Luminy PLA. It is made from renewable biomass, which growth absorbs CO2 from the atmosphere.

Messe Interpack

Kunststoff-Recycling

Kunststoff-Aufbereitung

Packaging Made from Greenhouse Gases

The plant is intended to produce an industrial large-scale volume of polylactic acid (PLA) polymer, utilizing lactic acid from corn as the primary feedstock.

Representatives of all contractual partners are looking forward to the first PLA plant in the MENA region.

thyssenkrupp Uhde to Build PLA Plant for MENA Region

Continuous production of sustainable particle foams based on renewable materials

Schaumstoffe

Schaumstoffe und Vorprodukte

Investigation of the foaming behaviour of polylactide and polylactide/poly(hydroxybutyrate-co-hydroxyvalerate) blends in particle foam extrusion

Traditionally used in products like food packaging and 3D printing, PLA is now proving its value in demanding injection molding applications. At Fakuma 2024 TotalEnergies Corbion showcases how their scientists are evolving Luminy PLA.

Messe Fakuma

Advancing Durable Plastic Sustainability with PLA

Thanks to enzymes, PLA should be able to degrade more quickly under natural environmental conditions in future – while retaining the same mechanical properties in use. Initial tests are promising.

Nachhaltigkeit

Umweltmanagement

Enzymes Accelerate PLA Degradation

Copolymer instead of  Plasticizer or Blend

Targeted Improvement in Elongation at Break and Impact Strength of PLA

Broader use of polylactide is hindered by its low elongation at break and impact strength. Attempts to overcome these difficulties so far have involved the use of plasticizers or blends. However, these both bring further problems with them. Copolymers of polyols and PLA offer a very appealing solution.

PLA’s elongation at break and impact strength stand in the way of its broader use. PLA copolymers look like a promising solution.

Polylactide (PLA), made from lactic acid, has become an established bio-based plastic in the packaging industry over the last decade. However, despite being widely accepted in the market, its low elongation at break and impact strength have acted as a brake on possible applications up to now. If PLA is to lend itself to the production of flexible packaging films, its properties need to be modified to match those of typical film materials like LDPE (low-density polyethylene) (Fig. 1).

Plasticized PLA compounds offer such modified properties. However, one of the difficulties with these compounds is that most known plasticizers have a tendency to migrate. That is why they have failed to make significant inroads into the market. For their part, various polyols have been shown to exert a plasticizing effect in PLA. However, such polyols display complex migration and crystallization behavior in binary blends. This severely limits the scope of application for the latter.

Through its development of PLA copolymers, SoBiCo GmbH has taken a different approach: the polyol contained in its copolymers of polyol and PLA is firmly and covalently bonded to the polymer (Fig. 2). This prevents the polyol from migrating and renders the PLA molecular chain more mobile. SoBiCo is currently launching the copolymers onto the market under the name Plactid.

Varying the polyol content allows their properties to be adjusted over a wide range: from stiff, PLA-like materials to materials with a property profile comparable to that of LDPE. Polyol contents of 10 and 20 % enable the elongation at break to be boosted to 100 to 400 % and the stiffness lowered to 2000 N/mm² to 200 N/mm² (Fig. 3).

The increase in mobility of the polymer chains in the PLA copolymer compared with those in PLA also has a substantial influence on the material’s crystallization tendency. Crystallization of PLA is slow and requires a narrow temperature window of around 100 °C. By contrast, PLA copolymers crystallize much faster and are less sensitive to deviations from the ideal crystallization temperature. This is illustrated by the comparison of the half-lives for crystallization of PLA and PLA copolymers of various polyol contents, as determined by isothermal DSC (differential scanning calorimetry) (Fig. 4). For example, at a polyol content of just 13 %, the crystallization half-life is more than halved and the temperature window for crystallization is extended to 20 °C, without any significant retardation.

Crystallization through  Targeted Stretching

An alternative to temperature-induced crystallization – which may entail long heating – is to induce crystallinity in PLA copolymers through targeted stretching. Crystallization through stretching is much less temperature-sensitive. A stretching factor of just two at temperatures above the glass transition temperature is sufficient to induce substantial crystallization of the PLA copolymers, accompanied by an increase in tensile strength. This opens up interesting possibilities, especially as regards conversion into mono- or biaxially oriented, soft films offering a combination of high elongation at break with good strength.

It is common knowledge that, due to the two enantiomers of lactic acid (L- and D-lactic acid), PLA offers the possibility of forming stereo-complexes, provided that different polymers are built up from pure L- and D-enantiomers (PLLA and PDLA, respectively). Because their melting temperature is roughly 40 °C higher, such stereo-complexes allow PLA to be used at higher service temperatures. A combination of PLA copolymers built up from L- and D-enantiomers, on one hand, and the technology of biaxially stretched films, on the other, could therefore open up completely new areas of application for bioplastics in film production. The available range of polyols additionally offers manifold development possibilities, such as grades featuring increased extensional viscosity, conferred by branched polyols.

Lowering the Glass-Transition Temperature of PLA to 20 °C

The biopolymer PLA is generally known for its low heat resistance. Possessing little to no crystallinity, the polymer is characterized by having a glass transition temperature of around 60 °C. In addition, PLA requires a narrow processing window of between 180 and 200 °C, being bounded by the melting temperature of about 170 °C and incipient thermal damage at 200 °C. PLA copolymers offer various approaches for changing this typical property profile. Because crystallization is much faster, the service temperature is not determined solely by the glass transition temperature. A high degree of crystallinity allows service at temperatures above the glass transition. For applications as a flexible film material, the glass transition temperature of the polymer should generally be lower than the service temperature. In the case of PLA polyol copolymers, the glass transition temperature of pure PLA (55 to 60 °C) can be greatly lowered with the help of polyols. For example, a Plactid copolymer with a polyol content of 20 % has a glass transition temperature of just 20 °C.

As already mentioned, stereo-complex crystals of separated, pure PLLA and PDLA polymers have higher melting temperatures. The opposite is true of PLA polymers in which L- and D- contents are contained in a single molecule (PLDLA). Their melting point and thus their processing temperature range can be lowered. For example, a D- content of 4 % in PLDLA lowers the melting temperature by approx. 16 °C (Table, copolymer 1).

However, the PLA loses its crystallization ability completely once the D- content in the polymer chain exceeds roughly 10 %. PLA polyol copolymers display surprisingly different behavior in this respect, too. For example, SoBiCo has succeeded in incorporating a D- content of 12 % (expressed in terms of the total amount of lactide) into a copolymer consisting of a wholly amorphous polyol (polyol content: 45 %) and a PLA, thus lowering the melting temperature to 120 °C (Table, copolymer 2). At the same time, despite the high D- content, the copolymer had a melting enthalpy of 12 J/g attributable to the PLA sequences.

Cost-Effective Production  in the Extruder

Aside from developments in the material itself, SoBiCo has succeeded in developing a cost-effective production process based on reactive compounding in the extruder. This combines two process steps that are usually separate: chemical synthesis of polymers and production of compounds based on such polymers. This integrated process developed by SoBiCo comprises polymerization, residual monomer extraction and compounding. The first production production line has a capacity of 2000 t/a, with plans for expansion to 10,000 t/a. In addition to the packaging applications which will be the main focus when production commences, SoBiCo intends to rapidly build up a broad portfolio of materials for processing by both extrusion and injection molding. The portfolio of Plactid copolymers will additionally be supplemented by the new Lacto product range (Lactofix, Lactoflex and Lactobatch), which can be used to modify conventional PLA.

SoBiCo GmbH  

https://sobico.de/

Ausgabenartikel

A view of the production of the PLA copolymer compounds: the proprietary process combines chemical synthesis of polymers and production of compounds in a single process.

Fig. 1. Comparison of properties of important plastics: PLA has only a low elongation at break, which makes it difficult to use, say, for films

Fig. 3. Influence of polyol content on elongation at break and modulus of elasticity of PLA copolymers: As the polyol content increases, elongation at break increases and the elastic modulus decreases.

Fig. 4. Half-life for crystallization of PLA and PLA copolymers analyzed by isothermal DSC: as the polyol content increases, the window of the processing temperature widens and the half-life decreases.

Table. Thermal properties of PLA and PLA copolymers.

Fig. 2. The polyol components are firmly integrated into the molecular chains of the copolymer.

KUint3_23_Sobico - Hauptartikel

PLA Copolymers: A solution for the Problem Areas of Bioplastics

Dr. Johannes Fuchs has been a Polymer-Gruppe employee since 2021 and Managing Director of SoBiCo since 2023.

The author would like to thank the Fraunhofer Institute for Applied Polymer Research (IAP), and especially Dr. Antje Lieske and her research group, for their extensive collaboration. The development of the PLA copolymers is largely the outcome of the long-standing, collaborative trust built up between Fraunhofer IAP and SoBiCo.

Read the German version of the article in our magazine Kunststoffe or at <a href="https://www.kunststoffe.de/a/fachartikel/copolymer-statt-weichmacher-oder-blend-3531146" target="_blank">www.kunststoffe.de</a>