Scope and Commercial Considerations

Our local and overseas study of boxes shows that for manufacturing economical  quality plastic in-ground boxes, two main materials are used.  Both of these are derived from the same base plastic material family referred to as polyolefin.  These came in a wide variety of grades and formula’s, which can slightly change the materials properties to suit their application and manufacturing process.

In this study we have only addressed Polypropylene (P.P.) and Polyethylene (P.E.) and the grades and properties that relate to in-ground box manufacture.


Main Box Material Considerations

Cost  P.P. has many similar properties to P.E. and was developed to further expand the usage of the usage of the Polyolefin market.  When it was first developed as a new material it was priced at the same as P.E.

Plastics are sold as a commodity with pricing directly reflecting supply and demand.  Designers quickly learning the superior properties of P.P. over the original P.E.  The increase in world demand for P.P. over P.E. has seen the raw material reach 20% above that of P.E. on the commodity market.

It is therefore fair to assume adopting a product made of P.P. will be more expensive in raw material costs and therefore have a higher manufactured unit cost to the same product made of P.E.


Technical Properties to Consider

There are many technical details.  I have reduced these down to the following key issues to be addressed specific to boxes.

  • UV stability
  • Chemical Resistance
  • Impact resistance
  • Deflection under load
  • Elastomeric recovery rates
  • Recycling
  • Comparative Industries material selection.
  • Ease of injection mounding and therefore consistency of finished quality.


UV Stability:

The Polyolefin plastic group do not perform well against UV and become brittle over time when exposed to natural sunlight.  The manufacturers can overcome this by including UV stabilizers into the material.  This is equally true for P.E. and P.P. with their UV properties being the same and the UV stabilizers being the same.  The quality and amount of UV Stabilizers used during the manufacture of the material directly determines the UV resistance and product life.

The cheapest and most effective UV stabilizer is carbon.  This is why most P.E. and P.P. products are black.  Polyolefin products with good quantities of black carbon UV stabilizers have been installed in outdoor installations in the NZ Agricultural industry. (Poly pipe, troughs, filters, tanks etc) for over 30 years with no significant product failure due to UV breakdown being reported where high quality UV stabilizers were used.

UV stabilizers in other colours are available, but are a lot more expensive.  With the failure of plastic domestic pipe systems in P.E. and butanol in the 1990’s many of the latest new pipe systems are now made of P.P. for industrial and domestic reticulation systems. These systems are coloured but do not need nor contain the costly coloured UV stabilizers as they are generally indoor or in-ground rated. This puts them out of the way of the harmful effect of the suns UV. In the water industry the trend is well established for indicating potable water by using the colour blue.  It is interesting to note for high quality blue UV stabilizers the cost per box lid is currently $1.04 more than the carbon black lid.  Currently there is no price difference charged for coloured lids over black lids.

So long as the box manufacturer is traceable through an ISO/9001 accreditation, and its manufacture specification, defines the type and amount of UV stabilizer used in the manufacture of the boxes, then I do not believe UV stability of Polyolefin products need be an issue.


Chemical Resistance:

The Chemical resistance properties of P.E. and P.P. are the same.  There is little chemical exposure to the boxes other than the possibilities of vehicle fuels and lubricants.  Both of these materials are capable of handling these products.  Hot roading mix being applied to the boxes present more of an issue due to the heat exposure rather than the chemicals.  P.P. has a recommended max heat exposure of 100oc against P.E.’s 85c rating.  There is little issue here with either material.


Impact Resistance:

This is an important issue for boxes with considerable difference between the properties of P.E. and P.P.  It also appears to be one of the reasons that designers are changing from P.E. to P.P. as the modern material of choice.  P.P. can have up to 200% greater impact resistance than P.E. which by nature is a more “floppy” polyolefin material.  P.E. can be made to be hard and firm but this greatly reduces the impact resistance with the material cracking on impact more easily the more rigid it is made.  Boxes must keep their shape once installed to allow proper compaction of backfill material and to ensure the lid can easily be removed and re-installed. Many  P.E. boxes sold in NZ have shown a tendency to deform easily. They have also gained a field reputation for cracking their plastic and the box lids going out of shape when the lid is removed.   This is more obvious in the larger sized boxes. Merchants have even reported that they had found that the P.E. boxes at the bottom of the pallet were found to have cracked under the weight of the boxes above them during transportation from the NZ manufacturer to their warehouse. While this can be caused by poor box design or manufacture, the superior impact and deflection resistance of P.P were the reason this new polyolefin was developed from the original P.E. materials.



The deflection rates shown on independent laboratory tests show that P.E. materials deflect between 50% to 100% more than P.P. for the same kg/cm2 weight loading.  The greater the deflection the less the protection for the componentry housed within the box.  Deflection directly affects the practical use of the boxes and the vehicle load rating as well as the boxes deforming during ground compaction.  Contractors have remarked that once they have removed the lid of a P.E. box it can be difficult to refit as the box opening had deformed or in fewer cases the side of the boxes deflected into the box cavity. This problem was especially apparent in the greater Auckland area where the use of longer P.E boxes to fit inline meter installations has been long established and the temperature of the cavity of the boxes can exceed 40 degrees centigrade during summer.

It does not seem to be a problem with imported nylon glass fibre reinforced large boxes or the locally produced P.P. large boxes. Sample ACUFLO boxes produced in P.E for comparative P.E. vs P.E. testing while proving stronger than comparable competitors boxes, still showed considerably more deflection and less shape recovery over a longer time than the same boxes manufactured in P.P.

In contrast an ACUFLO P.P box has been documented at a postal courier depot with constant courier van traffic over it every few minutes throughout the working day..  The box after five years is still fully functional, but the concrete around the box has fractured and broken down.


Elastomeric Recovery:

Deflection will always be found to some extent when any material is subjected to a loading.  In boxes subjected to vehicle use it is important that the box recovers to its shape once the load has been removed, otherwise the lid will not fit and surrounding paving can become hazardous. 

Following the application of a 2 ton weight over a P.E. box lid to simulate a heavy vehicle, the box lid deflected into the box cavity by 29mm. 24 hours after the removal of the weight the P.E lid recovered to between 70% and 80% of its original shape and size dimensions.

Following the same 2 ton deflection test, the P.P. deflected by only 12 mm and recovered to over 90% of its original shape within a 30 minutes.


Comparative Industries Material Selection:

While P.E. has been around for a long time increasingly the newer P.P. product seems to becoming more the polyolefin of choice.  Some of the reasons relate more to P.P.’s  beneficial properties during injection moulding, but there are industry trends that can be seen to directly relate to boxes.


Motor Industry:

With an increasing requirement for vehicles to include recyclable low cost materials reduced weight, and to be collision and pedestrian friendly, the industry has largely turned to plastics.

Plastic collision bumpers were originally made of P.E. in the 70’s and early 80’s.  There were found to discolour quickly with UV and cracked/split on impact and were replaced.  Today polyolefin bumpers are made of P.P. with the products success expanding its use to front guards, under car protection panels, engine protection covers and even complete secondary bonnets/engine covers.  Many modern vehicles are now rated for impacts over 15km without damage.  P.P. bumpers recover to their original shape immediately following a low speed collision.


Outdoor Furniture Industry:

Many of the original plastic outdoor furniture was found to be short lived through product failure.  The most demanding application is for public street seating. (bus stops, railway stations) and sports stadiums.  The move to P.P. for these applications has seen all the major new and refitted sports stadiums in NZ use coloured P.P. seating.

Increasingly the use of P.P. for pressure vessels ( i.e  filter housings ) over other materials ( such as Acetal and glass reinforced nylon ) has not only allowed more economical and quality assured manufacturing but also greater product performance with 25% higher working pressure being achieved . 



Both P.E. and P.P. are suitable for recycling and reuse for less demanding  injection moulded product.


In-ground Box Limitations

Traditionally Cast Iron has been the preferred box product for street use with wooden boxes being constructed for areas without vehicle exposure.

Plastic boxes have been available for over 20 years, with their use being limited to light vehicle areas such as footpaths and driveways.  This is due to plastic boxes being made of P.E. manufacture red by either injection moulding or rotary moulded.  The new P.P. materials we believe has the potential to allow plastic boxes when correctly designed and manufactured to have application for general street use.  The laboratory tests have shown the P.P. boxes withstand loadings of over 3500 and 5000 kgs.  This exceeds the gross wheel loading of even the maximum 40 ton trucks permitted on NZ roads.  Cast Iron boxes are expensive and the heavy lids present OSH hazards.  Aluminium is even more expensive and has increasingly become the target of theft due to its high scrap value.  Steel lids require a protective treatment such as galvanizing, which soon wears off and allows corrosion.  Steel in high wear areas tends to develop a polished finish (e.g. galvanized steel pipe hand rails), which becomes a pedestrian hazard as defined under the AS/NZS 3661.1 slip resistance national standard.

If a box design does not allow sufficient side ribbing to prevent  side wall flex ,this can lead to box collapse or contractors not compacting the material back around the box after installation through fear of damaging the box. This can lead to future subsidence and paving failure. Equally boxes with long curved radius corners make it difficult to pave up to the edges of the boxes. Where paving stones or tiles are used non square corners on the boxes can lead to a higher installation cost  and a poorer visual finish of the paved area.

ACUFLO believes that the future box market will continue to be dominated by the traditional cast iron products and the new plastic boxes.  The growth will come from the increasing application of plastic boxes into new applications and displacing traditional cast and aluminium products.

The P.P. material presently provides the greatest potential for the plastic boxes to grow in use due to its superior properties allowing a wider range of application to prove their suitability over time.


Conclusion and Recommendation 

There are seemingly endless polyolefin material variations, which directly affect the materials properties and pricing when reuse or recycled materials are used.

When comparing the two materials the range in % figures used in this report appear large. The figures used in this report are those supplied buy our raw material suppliers and the testing carried out on product independently of ACUFLO.

ACUFLO Industries Ltd is a mature NZ privately owned and professionally structured company with ISO 9001 accreditation and a proven commitment to NZ industry.  ACUFLO’s box range is now solely made from the preferred polypropylene polyolefin material and has proved superior under testing. ACUFLO boxes are proven under NZ conditions and withstanding its strong UV, through having had boxes in service for over 15 years.

If there is little or no market price difference to customers in price between boxes made of P.P over P.E., then the customers can gain more from a P.P box than achievable through using P.E. material. The use of the Polypropylene material while not as cheap as P.E. does allow a stronger box and protection of its contents, which in turn will provide customers with a lower overall cost of ownership.

Even where the price of P.P is slightly higher due to its higher raw material cost, an analysis of the cost of correcting failed boxes and the potential hazard they represent to street users needs to be taken into consideration when assessing the justification for paying slightly more in initial capital cost for the benefits of a box made of Polypropylene.



Craig Benseman


Factory Manager

ACUFLO Industries LTD


On behalf of ACUFLO Industries Ltd