The strength of specimens made from 100% virgin material was found  to  have  an  average  of  45.2  MPa  with  a  standard  deviation of  1.68  MPa.  The  50/50  blend  yielded  an  average  UTS  of  37.1MPa with a standard deviation of 2.56 MPa, and the 75/25 blend was  slightly  stronger  with  an  average  UTS  of  41.2  MPa  and  a standard  deviation  of  1.45  MPa. As  expected,  the  corresponding strength  of  specimens  made  from  100%  recycled  material  was much weaker, with an average of 21.1 MPa and a standard deviation  of  2.14  MPa.  Thus,  products  made  from  the  virgin  material were  both  twice  as  strong  and  more  consistent  than  those  made from  the  recycled  material.  This  dramatic  weakness  of  recycled products, which can be attributed to the lowered material molecular  weight  and  associated  lessened  degree  of  molecular  entanglement  within  products,  is  a  major  reason  for  the  severely  limited usage  of  recycled  polymers  to  date.
Fig. 1 Tensile strength distributions of conventionally molded
products made from blends of new and recycled material
 
Fig. 2 Cavity pressure profile  of control sample: (a)P1 and P2 of 100/0,(b)P1 and P2 of 75/25,(c)P1 and P2 of 50/50,and (d) pressure difference between P1 and P2 of 100/0,75/25 snd 50/50

Figures 2~a!–2~c! contain typical measured cavity pressure profiles   for  the  conventional  molding  of  100/0,  75/25,  and  50/50  recycled  PS  blends.  The  pressure  data  shown  was  recorded  at  the pressure  sensor  locations  P1  and  P2  in  the  mold  cavity.  P1  is located in the gate end grip section of the specimen, whereas P2 is in  the  grip  section  opposite  the  gate.  It  is  clearly  seen  that  the pressure decreases with time during the molding cycle. This is due to  the  change  in  viscosity  and  the  volumetric  shrinkage.  In  conventional molding processes, the polymer shrinks and its viscosity increases  toward  the  end  of  the  cycle  because  the  polymer  temperature decreases. Figure 2~d! presents the temporal pressure difference  between  P1  and  P2  for  these  three  blends.  For  the  100/0,the pressure difference increases with time during the cycle. This is due to the packing pressure, which gradually packs more material  into  the  cavity  in  order  to  compensate  for  the  subsequent shrinkage. However, the processing at the 75/25 and 50/50 blends did  not  show  this  type  of  behavior.  This  may  be  due  to  the  low molecular  weight  material  that  is  contained  in  these  blends.  Because  of  the  low  molecular  weight,  the  solidification   behavior  is likely  to  be  accelerated  or  changed,  and  thus  localized  solidification  may  have  been  achieved  prior  to  the  application  of  extra packing  pressure.
In comparison, Figs. 3 (a) and 3 (b) present sample pressure profiles   at  the  pressure  sensor  locations  P1  and  P2  during  VAIM processing  witha2 Hz vibration  frequency.  The  pressure  profile during  the VAIM  process  is  quite  different  from  that  for  conventional  molding  as  the  pressures  fluctuates   corresponding  to  the manipulation  of  the  melt  in  the  cavity  in  a  compression  and/or decompression manner. Furthermore, the pressure at P1 fluctuates with a larger amplitude than that at P2. Once again, P1 is closer to the  gate  than  P2.  This  explains  that  the  localized  effects  of  the vibration may be a function of the distance between the vibration source  and  the  particular  local  region  of  the  melt.  Figure  3(c) represents  the  pressure  difference  between  P1  and  P2.  Note  how the  amplitude  reverses  sign (i.e., P2 . P1),  resulting  in  an  oscillating  flow   that  is  not  seen  during  conventional  molding  processes. 回收塑料材料注射成型英文文献和中文翻译(6):http://www.youerw.com/fanyi/lunwen_17270.html