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Novel Injection Moulding Processing for the Production of Low Density Foams based on Innovative Granule Technology

Periodic Report Summary 2 - LIGHT-FOAM (Novel Injection Moulding Processing for the Production of Low Density Foams based on Innovative Granule Technology)

Project Context and Objectives:

The overall objective of the Light-Foam project is to develop a novel polymer processing technology to foam engineering grade thermoplastics without the need for chemical blowing agents or speciality moulding/extrusion equipment achieving lower densities than are possible through current state of art. Enhanced scientific knowledge will be developed in the fields of gas solubility and permeation within polymers enabling development of:
• A commercial process using autoclave technology to infuse high levels of nitrogen into engineering grade polymer granules. This process is carried out above the glass transition temperature (Tg) of the polymer, the granules are then cooled to room temperature so reducing their free volume and trapping nitrogen molecules within the polymer.
• A packaging solution to minimise nitrogen loss during storage which is cost effective and will enable shipment of granules to end-users.
• Injection Moulding and Extrusion processing of nitrogen infused granules creating uniform nucleation and growth of nitrogen bubbles within the polymer (once beyond the injection point/die) and the production of high performance case study parts in order to display the benefits of the technology.
More specifically the technology allows:
• Higher production rates in injection moulding & extrusion equipment.
• Cost competitive options for low production runs.
• Use with standard moulding and extrusion machines.
A list summarising the scientific and technological objectives is as follows:
Scientific Objectives: To gain sufficient extension to the current knowledge of:
• Gas infusion and molecular dissolution and diffusion of nitrogen in polymers, specifically relating to granules and melts
• How to determine nitrogen retention and saturation of thermoplastic granules
• Understanding ideal conditions for nitrogen gas infusion into the selected case study engineering thermoplastics
Technological Objectives:
• Commercial process which uses large scale autoclave technology to infuse high levels of nitrogen into a range of engineering polymer granules.
• A novel packaging package solution to transport and store treated granules
• Optimisation of injection moulding and extrusion parameters for processing speed, density reduction and mechanical performance.

Project Results:
Work Package 1 – Development of Gas Dissolution & Diffusion Models.
The consortium selected 5 case study materials, PEEK, PC, PA66, PET and ABS. These were selected on the basis of use by either the end users within the consortium or likely use within the membership of the SME-AG’s membership. A review of scientific literature regarding nitrogen retention in polymer systems and the relationships between storage times, temperature, pressure and initial nitrogen saturation was completed. A lab-scale test cell was designed, built and commissioned in order to accurately determine the levels of nitrogen infused into thermoplastic granules identified as case study materials. A predictive model was built to predict nitrogen adsorption and desorption behaviour of polymer granules.
Work Package 2 – Development of Nitrogen Dissolution & Diffusion Models.
Lab-scale diffusion and dissolution trials were undertaken on the case study materials and data provided to enable initial granule treatments of larger batches of material in autoclave conditions. Results were compared to the model predictions and further validation and enhancement of the software model completed. Close attention was given to the current autoclave processing parameters in order to ensure the end-user can maintain full processing capacities. Dissolution and diffusion rates were established for the case study materials. This served to enhance the software models to degree whereby predicted diffusion and diffusion rates are very close to actual results. Larger batches of material were treated in autoclave conditions (25Kg) to enable further trials by each of the SME end-users within their respective technologies (injection moulding, compression moulding & extrusion.
Work Package 3 – Development of Granule Packaging System. An initial packaging specification was created following a literature review of legislation concerning transportation of goods held under pressure. Option B (pressure vessel) as described in task 3.2 of the Annex 1 was discounted by the consortium as it is considered too expensive, therefore focus was given to option A (container) which could be manufactured by Structure-Flex. Lab-scale trials were conducted to determine the internal pressures that the packaging would need to withstand. Following this research was undertaken to determine candidate low permeability polymer materials that would be cost competitive. Low permeability fabrics were first considered and initial samples made using materials commonly used for automotive airbags. Prototype packaging was made and permeation trials were undertaken under a range of temperatures with gassed granules. A second, less costly option was also considered which incorporated a multi-layered combination of polyolefin and aluminium into which a one-way valve was included to act as a vent in the event of high pressure build up. As this option was considered more cost effective, a number of 25Kg bags were manufactured with valve and filled with either gassed or un-gassed PC. Storage trials were undertaken in refrigerated, ambient and high temperatures with good results.
Work Package 4 – Injection Moulding & Extrusion Conditions. An injection moulded case study part was discussed and agreed between Tecnostamp and UK MatRI which was a ‘spinning-top’ shape of four diameters. Initial trials were conducted by UK MatRI in which injection mould parameters were established for HDPE, glass-filled PA66 and PC for both un-gassed and gassed granules and processing parameters determined for un-gassed and gassed granules. The mould tool was then shipped to Tecnostamp where following some modifications to enable automatic operation the trials were repeated, however, Tecnostamp didn’t use the same set of processing parameters as advised by UK MatRI and the trials weren’t as successful. The trials were undertaken again at UK MatRI using the original conditions and the success of the first trials repeated. The most difficult parameter to achieve is surface finish however, a 52% weight saving was proven for a part made from gassed granules, significant cycle-time reductions were also obtained. A high number of extrusion trials were carried out at Polinter. Extrusion trials were conducted using three die profiles, PC and gassed PC mixed in various proportions to allow the effects of nitrogen level, extrusion parameters and die design on the extruded product to be established. It has been shown that die design, processing parameters such as die temperature and material mix can be used to influence density, mechanical properties and product microstructure. Density reduction of up to 40% in comparison between LF and PC material was obtained for gassed polymers which have been received 48 hours after processing at Zotefoams. Gassed PC granules stored in -20°C after three months are still able to yield up to 18% reduction in density compared to virgin PC.
Work Package 5 – Evaluation of Foamed Parts.
A range of case study materials were selected namely PA6 and PEEK for production using injection moulding and PC was selected for production using an extrusion process. Foamed and virgin samples were produced from injection and extrusion processes and sent to UKMatri for physical and mechanical evaluation. Results show a reduction in density of up to 10% for foamed PEEK, 35% for foamed PA6 and 49% for foamed PC. Microscopy images show that pore sizes range from 50 to 500 μm in the cross sections of the different case study materials produced by different methods. Injection moulding of foamed PEEK shows the most homogeneous distribution of pores with the lowest pore size distribution. Mechanical testing of injection moulded parts show that foamed PEEK samples give a 15% reduction in mechanical properties to virgin PEEK foamed PA6 samples show 10 to 20% reduction in mechanical properties compared to virgin PA6 samples. Mechanical results from samples produced by extrusion show that foamed PC can improve the mechanical properties up to 42% with incorporation of 25% LF at 35 rpm, but can reduce the mechanical properties by up to 58% at screw speeds of 19rpm.
Work Package 6 – Technology Demonstration
Three case study parts have been manufactured, the ‘spinning-top’ for Injection Moulding demonstration, a square profile for extrusion demonstration and a drinks cabinet for compression moulding techniques. Each of the case study parts is available to the beneficiaries within the consortium in order to be able to demonstrate the technology to specific targeted end-users.
Work-Package 7 – Training, Dissemination & Exploitation.
The Lightfoam technology has been actively disseminated throughout the course of the project by each of the SME-AG’s. A web-site (www.lightfoam.pera.com) has been created and included on all literature. The Technology has been disseminated at major plastics trade events such as Interplas (UK), PlastPol (Poland) and Euromould (Germany). The coordinator has published a prject promotional brochure which can be obtained in English, Spanish and Estonian, these have been passed on to the respective SME-AG’s and to the SME beneficiaries in the project. The dissemination activities have led to enquiries from companies interested in the technology and to date there are two commercial opportunities. The consortium has discussed exploitation and agreed a plan to pursue after the end of the project.
Work-Package 8 – Technical Project Management Including Innovation Related Activities.
The consortium maintained a high level of communication throughout the course of the project so enabling a thorough understanding of specific technical and process constraints to be overcome within each company in order to ensure production, storage, transport and processing of nitrogen infused granules. Results of trials were openly shared by all beneficiaries who all hosted consortium and technical meetings. A Patent search was conducted to ensure that the technology is novel. Where any risk was identified the appropriate RTD undertook additional measures to analyse and resolve the issue. The coordinator is currently pursuing protection of the technology.
Work Package 9 – Consortium Management.
The coordinator has maintained a good level of communication with the EC Project Officer and within the consortium. Consortium meetings have taken place on a quarterly basis as well as technical meetings as and when deemed necessary. All reports have been uploaded to the project website so that the partners can access the information.

Potential Impact:
The overall technological aim of the LIGHTFOAM project is to develop a novel polymer processing technology to foam engineering grade thermoplastics without the need for chemical blowing agents or special moulding or extrusion equipment. The technology will a) enable manufacture of parts at higher production rates, b) provide a cost competitive option for low production runs, c) be suitable for use with standard moulding and extrusion machines, d) produce high quality foamed parts with fine micro-cellular structures and densities in the range of 30% - 70%.

List of Websites:

http://www.lightfoam.pera.com