CLEAR POLYPROPYLENE FLYING HIGH

A shortage of polycarbonate and consequent higher prices, combined with an increasing level of breakages of Atlas in-flight catering drawer made from the polymer, led Lufthansa Catering Logistik (LCL) to undertake a review of materials with the potential to overcome supply and cost issues, as well as provide a reduced breakage solution.

LCL is responsible for serving the entire airline industry with in-flight equipment and logistic systems, and its in-house team of experts has extensive experience in developing both individual items and complete on-board concepts to improve and advance in-flight catering.

The new ATLAS standard design of LCL’s catering drawer in Millad® clarified polypropylene (cPP) complies fully with the mechanical and optical performance demands of the airline industry, while reducing by 50 percent the rate of replacements needed compared with its predecessor moulded in polycarbonate. Thereby making a major contribution to cost savings without compromising performance or aesthetics

These customised drawers are provided to the catering units, who are the interface between LCL and its airline customers, for the transportation of in-flight meals and beverages to individual flights on a just-in-time basis. When filled, the drawers are placed in trolleys which slot into an industry standard container in the plane’s galley.

Originally introduced in the ‘70s, the ATLAS inflight catering drawer was manufactured in transparent polycarbonate. The combination of low weight, stiffness and ‘see-through’ optical clarity were the key drivers for this material at that time. A major issue however, was drawer breakage as a result of improper use or stress cracking caused by the long-term impact of the increasingly aggressive cleaning chemicals as well as hot water being used in catering operations.

According to Thomas Köhler, Product Manager for in-flight service equipment at LCL: “By mid-2000 the shortage of polycarbonate and its escalating price, coupled with the demand for broken drawer replacements at LCL customers, which we are averaging 70 percent a year, caused LCL to look for an adequate alternative.”

A list of resin property requirements was established. Key criteria to be met were: heat stability, chemical resistance, optical clarity, mechanical performance, including impact resistance and tensile strength, and resin price. Among the resins considered were PSU, PES, PMMA, CP, COC, PETG, HI-PS and clarified PP (cPP). Trials using the existing drawer mould were carried out with various resins to determine their performance.

Based on the performance/cost matrix the material exhibiting the optimum fit was a metallocene PP clarified with Millad® 3988. However, although this specific clarified PP (cPP) had a higher E-modulus than any of the other clear polypropylene resins considered, at 1700 N/mm² it was still far below PCs 2400 N/mm². But, after detailed analysis of stress and loading factors for the existing PC drawer, Köhler established that despite the lower strength of PP resin it met the overall objective which was to achieve the initial level of product stability offered by PC.

Consequently, the drawer design was optimised for cPP. Once the product specification was drawn up, LCL, together with the injection moulder Terö-Plastik and the engineering company Mann, developed a cPP specific design. Using FEM technology and other software tools, the design was fully optimised through the addition of reinforcing ribs to strengthen the bottom and side panels, the adjustment of wall-thicknesses to avoid thermal distortion and the inclusion of a reinforced handle section.

In November 2000, Lufthansa gave its approval for the cPP drawer and the first production lots were sold. The reaction from the airlines was extremely positive. So positive, that within two months the investment in the new mould was recuperated.

Says Köhler: “A decreasing need for replacements became apparent after only a short introductionary phase. Which, in addition to lower raw materi