Lightweight boards, quality and carbon footprints

Research conducted for M-real Consumer Packaging used box compression tests to study the performance of cartonboard packaging in real-life situations such as stacking and palletising.

The tests have confirmed that lighter weight boards can be used without compromising the quality or performance of finished cartons, resulting in both cost savings and sustainability benefits as less raw material is required in their manufacture.

The studies, undertaken by an external research institute, performed box compression tests on dummy cartons. Results showed that the bending stiffness of a board shows the best correlation with the box compression strength. Higher bending stiffness improves the board’s resistance to bulging and cracking, creating cartons with higher rigidity.

Good rigidity and high stacking strength are particularly needed when cartons are loaded onto pallets on top of each other and secondary packaging, such as a corrugated case, is not being used. In such end uses it is vital to choose the right raw material for cartons.

M-real’s grades with high bulk and optimised layer structures demonstrate very good stiffness for a given grammage. In a market where substance equals weight, and heavier weight equals higher cost, it becomes apparent that desirable carton rigidity can be achieved in tandem with cost savings. A better quality carton can decrease the amount of wasted products and even eliminate the need for slip sheets during stacking, saving the additional cost of using these altogether.

Further box compression tests evaluated how different design elements - specifically carton dimension or board fibre direction - and surrounding climate conditions can affect carton strength. The results found that changing carton size - height and width of the side panels – had no notable effect on the BCT value, as it is the corners that bear most of the load.

Rotating fibre direction can, however, make a dramatic difference. Most cartons use horizontal fibre direction, to improve runnability on the packaging lines and give more rigid feel when handled. But when fibre direction was changed to run parallel to compression, stacking strength was increased as much as 20%. This benefit has, however, to be weighed against the more usually accepted advantages of horizontal fibre direction mentioned above.

Finally, tests found that increasing the relative humidity of air lowers the strength of a board because it is made from a natural raw material - wood fibre. Both board and carton strength decreased when relative humidity rose from 50 to 80%. Box compression strength decreased 15-25%, depending on board grade. This is important to consider when cartons are exposed to humid conditions during transport or storage.

Matthew Terry, Technical Service Manager M-real Consumer Packaging, says: “Today, cartons are required to meet the standards of the retail chain in both quality and functionality. They not only need to protect and promote the product, but also to be cost efficient and enable efficient handling in the areas where the highest costs are incurred. Our studies have highlighted the critical points encountered in the packaging value chain and established what demands they make on a board’s raw materials as well as on the finished carton.”

Lighter weight boards also reduce carbon footprints

New research, also conducted for M-real Consumer Packaging, has found that within the same grade (brand), the carbon footprint of a cartonboard reduces at least in proportion to its basis weight. A 15% reduction in board weight equates to an 18% reduction in carbon footprint, which is important to users concerned about sustainability. If they can specify a lighter weight board, provided all criteria regarding stiffness and performance are met, their own carbon footprint will diminish accordingly.

For example, M-real has calculated that if you make 100,000 biscuit cartons using a 25 g/m² lighter board, the CO₂ saving per annum equals driving 1000 km by car.

The research, commissioned from an external research institute, aimed to produce life cycle assessments for three different weights of board. Carbon footprints were calculated for 10,000 biscuit cartons produced in 250, 270 and 295 g/m² weights, to discover if the footprint would reduce proportionately when a lighter weight board was used.

Calculations assessed energy used in forestry, transport and manufacturing at all stages from harvesting the wood to making the cartons, including, for example, transporting the board to the customer.

M-real Consumer Packaging (www.m-real.com) is distributed in Australia by Paper Agencies Pty Ltd.